Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 1 | .. _glossary: |
| 2 | |
| 3 | ******** |
| 4 | Glossary |
| 5 | ******** |
| 6 | |
| 7 | .. if you add new entries, keep the alphabetical sorting! |
| 8 | |
| 9 | .. glossary:: |
| 10 | |
| 11 | ``>>>`` |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 12 | The default Python prompt of the interactive shell. Often seen for code |
| 13 | examples which can be executed interactively in the interpreter. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 14 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 15 | ``...`` |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 16 | The default Python prompt of the interactive shell when entering code for |
| 17 | an indented code block or within a pair of matching left and right |
| 18 | delimiters (parentheses, square brackets or curly braces). |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 19 | |
Benjamin Peterson | d631371 | 2008-07-31 16:23:04 +0000 | [diff] [blame] | 20 | 2to3 |
| 21 | A tool that tries to convert Python 2.x code to Python 3.x code by |
Georg Brandl | 6faee4e | 2010-09-21 14:48:28 +0000 | [diff] [blame] | 22 | handling most of the incompatibilities which can be detected by parsing the |
Benjamin Peterson | d631371 | 2008-07-31 16:23:04 +0000 | [diff] [blame] | 23 | source and traversing the parse tree. |
| 24 | |
| 25 | 2to3 is available in the standard library as :mod:`lib2to3`; a standalone |
| 26 | entry point is provided as :file:`Tools/scripts/2to3`. See |
| 27 | :ref:`2to3-reference`. |
| 28 | |
Georg Brandl | 86b2fb9 | 2008-07-16 03:43:04 +0000 | [diff] [blame] | 29 | abstract base class |
Éric Araujo | fa088db | 2011-06-04 18:42:38 +0200 | [diff] [blame] | 30 | Abstract base classes complement :term:`duck-typing` by |
Georg Brandl | 22b3431 | 2009-07-26 14:54:51 +0000 | [diff] [blame] | 31 | providing a way to define interfaces when other techniques like |
Éric Araujo | fa088db | 2011-06-04 18:42:38 +0200 | [diff] [blame] | 32 | :func:`hasattr` would be clumsy or subtly wrong (for example with |
Éric Araujo | 04ac59a | 2011-08-19 09:07:46 +0200 | [diff] [blame] | 33 | :ref:`magic methods <special-lookup>`). ABCs introduce virtual |
| 34 | subclasses, which are classes that don't inherit from a class but are |
| 35 | still recognized by :func:`isinstance` and :func:`issubclass`; see the |
| 36 | :mod:`abc` module documentation. Python comes with many built-in ABCs for |
Éric Araujo | 459b452 | 2011-06-04 21:16:42 +0200 | [diff] [blame] | 37 | data structures (in the :mod:`collections.abc` module), numbers (in the |
Éric Araujo | fa088db | 2011-06-04 18:42:38 +0200 | [diff] [blame] | 38 | :mod:`numbers` module), streams (in the :mod:`io` module), import finders |
| 39 | and loaders (in the :mod:`importlib.abc` module). You can create your own |
| 40 | ABCs with the :mod:`abc` module. |
Benjamin Peterson | 4118174 | 2008-07-02 20:22:54 +0000 | [diff] [blame] | 41 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 42 | argument |
Chris Jerdonek | c2a7fd6 | 2012-11-28 02:29:33 -0800 | [diff] [blame] | 43 | A value passed to a :term:`function` (or :term:`method`) when calling the |
| 44 | function. There are two types of arguments: |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 45 | |
Chris Jerdonek | c2a7fd6 | 2012-11-28 02:29:33 -0800 | [diff] [blame] | 46 | * :dfn:`keyword argument`: an argument preceded by an identifier (e.g. |
| 47 | ``name=``) in a function call or passed as a value in a dictionary |
| 48 | preceded by ``**``. For example, ``3`` and ``5`` are both keyword |
| 49 | arguments in the following calls to :func:`complex`:: |
| 50 | |
| 51 | complex(real=3, imag=5) |
| 52 | complex(**{'real': 3, 'imag': 5}) |
| 53 | |
| 54 | * :dfn:`positional argument`: an argument that is not a keyword argument. |
| 55 | Positional arguments can appear at the beginning of an argument list |
| 56 | and/or be passed as elements of an :term:`iterable` preceded by ``*``. |
| 57 | For example, ``3`` and ``5`` are both positional arguments in the |
| 58 | following calls:: |
| 59 | |
| 60 | complex(3, 5) |
| 61 | complex(*(3, 5)) |
| 62 | |
| 63 | Arguments are assigned to the named local variables in a function body. |
| 64 | See the :ref:`calls` section for the rules governing this assignment. |
| 65 | Syntactically, any expression can be used to represent an argument; the |
| 66 | evaluated value is assigned to the local variable. |
| 67 | |
| 68 | See also the :term:`parameter` glossary entry, the FAQ question on |
| 69 | :ref:`the difference between arguments and parameters |
| 70 | <faq-argument-vs-parameter>`, and :pep:`362`. |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 71 | |
| 72 | attribute |
| 73 | A value associated with an object which is referenced by name using |
| 74 | dotted expressions. For example, if an object *o* has an attribute |
| 75 | *a* it would be referenced as *o.a*. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 76 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 77 | BDFL |
| 78 | Benevolent Dictator For Life, a.k.a. `Guido van Rossum |
| 79 | <http://www.python.org/~guido/>`_, Python's creator. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 80 | |
Ezio Melotti | aa54e2f | 2013-04-30 23:33:31 +0300 | [diff] [blame] | 81 | bytes-like object |
Antoine Pitrou | 5de183a | 2013-05-04 20:18:34 +0200 | [diff] [blame] | 82 | An object that supports the :ref:`bufferobjects`, like :class:`bytes`, |
| 83 | :class:`bytearray` or :class:`memoryview`. Bytes-like objects can |
| 84 | be used for various operations that expect binary data, such as |
| 85 | compression, saving to a binary file or sending over a socket. |
| 86 | Some operations need the binary data to be mutable, in which case |
| 87 | not all bytes-like objects can apply. |
Ezio Melotti | aa54e2f | 2013-04-30 23:33:31 +0300 | [diff] [blame] | 88 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 89 | bytecode |
| 90 | Python source code is compiled into bytecode, the internal representation |
Brett Cannon | 8315fd1 | 2010-07-02 22:03:00 +0000 | [diff] [blame] | 91 | of a Python program in the CPython interpreter. The bytecode is also |
| 92 | cached in ``.pyc`` and ``.pyo`` files so that executing the same file is |
| 93 | faster the second time (recompilation from source to bytecode can be |
| 94 | avoided). This "intermediate language" is said to run on a |
| 95 | :term:`virtual machine` that executes the machine code corresponding to |
| 96 | each bytecode. Do note that bytecodes are not expected to work between |
| 97 | different Python virtual machines, nor to be stable between Python |
| 98 | releases. |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 99 | |
Georg Brandl | 2cb72d3 | 2010-07-03 10:26:54 +0000 | [diff] [blame] | 100 | A list of bytecode instructions can be found in the documentation for |
| 101 | :ref:`the dis module <bytecodes>`. |
| 102 | |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 103 | class |
| 104 | A template for creating user-defined objects. Class definitions |
| 105 | normally contain method definitions which operate on instances of the |
| 106 | class. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 107 | |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 108 | coercion |
| 109 | The implicit conversion of an instance of one type to another during an |
| 110 | operation which involves two arguments of the same type. For example, |
| 111 | ``int(3.15)`` converts the floating point number to the integer ``3``, but |
| 112 | in ``3+4.5``, each argument is of a different type (one int, one float), |
| 113 | and both must be converted to the same type before they can be added or it |
Benjamin Peterson | 2d71822 | 2008-11-21 00:25:02 +0000 | [diff] [blame] | 114 | will raise a ``TypeError``. Without coercion, all arguments of even |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 115 | compatible types would have to be normalized to the same value by the |
| 116 | programmer, e.g., ``float(3)+4.5`` rather than just ``3+4.5``. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 117 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 118 | complex number |
| 119 | An extension of the familiar real number system in which all numbers are |
| 120 | expressed as a sum of a real part and an imaginary part. Imaginary |
| 121 | numbers are real multiples of the imaginary unit (the square root of |
| 122 | ``-1``), often written ``i`` in mathematics or ``j`` in |
Georg Brandl | 22b3431 | 2009-07-26 14:54:51 +0000 | [diff] [blame] | 123 | engineering. Python has built-in support for complex numbers, which are |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 124 | written with this latter notation; the imaginary part is written with a |
| 125 | ``j`` suffix, e.g., ``3+1j``. To get access to complex equivalents of the |
| 126 | :mod:`math` module, use :mod:`cmath`. Use of complex numbers is a fairly |
| 127 | advanced mathematical feature. If you're not aware of a need for them, |
| 128 | it's almost certain you can safely ignore them. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 129 | |
Christian Heimes | 895627f | 2007-12-08 17:28:33 +0000 | [diff] [blame] | 130 | context manager |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 131 | An object which controls the environment seen in a :keyword:`with` |
Christian Heimes | 895627f | 2007-12-08 17:28:33 +0000 | [diff] [blame] | 132 | statement by defining :meth:`__enter__` and :meth:`__exit__` methods. |
| 133 | See :pep:`343`. |
| 134 | |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 135 | CPython |
Antoine Pitrou | 0034281 | 2011-01-06 16:31:28 +0000 | [diff] [blame] | 136 | The canonical implementation of the Python programming language, as |
| 137 | distributed on `python.org <http://python.org>`_. The term "CPython" |
| 138 | is used when necessary to distinguish this implementation from others |
| 139 | such as Jython or IronPython. |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 140 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 141 | decorator |
| 142 | A function returning another function, usually applied as a function |
| 143 | transformation using the ``@wrapper`` syntax. Common examples for |
| 144 | decorators are :func:`classmethod` and :func:`staticmethod`. |
| 145 | |
| 146 | The decorator syntax is merely syntactic sugar, the following two |
| 147 | function definitions are semantically equivalent:: |
| 148 | |
| 149 | def f(...): |
| 150 | ... |
| 151 | f = staticmethod(f) |
| 152 | |
| 153 | @staticmethod |
| 154 | def f(...): |
| 155 | ... |
| 156 | |
Georg Brandl | af265f4 | 2008-12-07 15:06:20 +0000 | [diff] [blame] | 157 | The same concept exists for classes, but is less commonly used there. See |
| 158 | the documentation for :ref:`function definitions <function>` and |
| 159 | :ref:`class definitions <class>` for more about decorators. |
Georg Brandl | a09ca38 | 2007-12-02 18:20:12 +0000 | [diff] [blame] | 160 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 161 | descriptor |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 162 | Any object which defines the methods :meth:`__get__`, :meth:`__set__`, or |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 163 | :meth:`__delete__`. When a class attribute is a descriptor, its special |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 164 | binding behavior is triggered upon attribute lookup. Normally, using |
| 165 | *a.b* to get, set or delete an attribute looks up the object named *b* in |
| 166 | the class dictionary for *a*, but if *b* is a descriptor, the respective |
| 167 | descriptor method gets called. Understanding descriptors is a key to a |
| 168 | deep understanding of Python because they are the basis for many features |
| 169 | including functions, methods, properties, class methods, static methods, |
| 170 | and reference to super classes. |
| 171 | |
| 172 | For more information about descriptors' methods, see :ref:`descriptors`. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 173 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 174 | dictionary |
Senthil Kumaran | 6080db7 | 2012-03-12 10:05:34 -0700 | [diff] [blame] | 175 | An associative array, where arbitrary keys are mapped to values. The |
| 176 | keys can be any object with :meth:`__hash__` and :meth:`__eq__` methods. |
| 177 | Called a hash in Perl. |
Georg Brandl | 3dbca81 | 2008-07-23 16:10:53 +0000 | [diff] [blame] | 178 | |
| 179 | docstring |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 180 | A string literal which appears as the first expression in a class, |
| 181 | function or module. While ignored when the suite is executed, it is |
| 182 | recognized by the compiler and put into the :attr:`__doc__` attribute |
| 183 | of the enclosing class, function or module. Since it is available via |
| 184 | introspection, it is the canonical place for documentation of the |
Georg Brandl | 3dbca81 | 2008-07-23 16:10:53 +0000 | [diff] [blame] | 185 | object. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 186 | |
| 187 | duck-typing |
Georg Brandl | 73b1c7b | 2010-07-10 10:39:57 +0000 | [diff] [blame] | 188 | A programming style which does not look at an object's type to determine |
| 189 | if it has the right interface; instead, the method or attribute is simply |
| 190 | called or used ("If it looks like a duck and quacks like a duck, it |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 191 | must be a duck.") By emphasizing interfaces rather than specific types, |
| 192 | well-designed code improves its flexibility by allowing polymorphic |
| 193 | substitution. Duck-typing avoids tests using :func:`type` or |
Georg Brandl | 8a1c254 | 2010-07-11 08:36:20 +0000 | [diff] [blame] | 194 | :func:`isinstance`. (Note, however, that duck-typing can be complemented |
Éric Araujo | 0519b09 | 2011-08-19 00:39:19 +0200 | [diff] [blame] | 195 | with :term:`abstract base classes <abstract base class>`.) Instead, it |
| 196 | typically employs :func:`hasattr` tests or :term:`EAFP` programming. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 197 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 198 | EAFP |
| 199 | Easier to ask for forgiveness than permission. This common Python coding |
| 200 | style assumes the existence of valid keys or attributes and catches |
| 201 | exceptions if the assumption proves false. This clean and fast style is |
| 202 | characterized by the presence of many :keyword:`try` and :keyword:`except` |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 203 | statements. The technique contrasts with the :term:`LBYL` style |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 204 | common to many other languages such as C. |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 205 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 206 | expression |
| 207 | A piece of syntax which can be evaluated to some value. In other words, |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 208 | an expression is an accumulation of expression elements like literals, |
| 209 | names, attribute access, operators or function calls which all return a |
| 210 | value. In contrast to many other languages, not all language constructs |
| 211 | are expressions. There are also :term:`statement`\s which cannot be used |
| 212 | as expressions, such as :keyword:`if`. Assignments are also statements, |
| 213 | not expressions. |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 214 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 215 | extension module |
Georg Brandl | 9d9848e | 2010-12-28 11:48:53 +0000 | [diff] [blame] | 216 | A module written in C or C++, using Python's C API to interact with the |
| 217 | core and with user code. |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 218 | |
Antoine Pitrou | 0b65b0f | 2010-09-15 09:58:26 +0000 | [diff] [blame] | 219 | file object |
| 220 | An object exposing a file-oriented API (with methods such as |
Georg Brandl | 9d9848e | 2010-12-28 11:48:53 +0000 | [diff] [blame] | 221 | :meth:`read()` or :meth:`write()`) to an underlying resource. Depending |
| 222 | on the way it was created, a file object can mediate access to a real |
Eli Bendersky | dbaedb8 | 2012-03-30 11:02:05 +0300 | [diff] [blame] | 223 | on-disk file or to another type of storage or communication device |
Georg Brandl | 9d9848e | 2010-12-28 11:48:53 +0000 | [diff] [blame] | 224 | (for example standard input/output, in-memory buffers, sockets, pipes, |
| 225 | etc.). File objects are also called :dfn:`file-like objects` or |
| 226 | :dfn:`streams`. |
Antoine Pitrou | 0b65b0f | 2010-09-15 09:58:26 +0000 | [diff] [blame] | 227 | |
Georg Brandl | 9d9848e | 2010-12-28 11:48:53 +0000 | [diff] [blame] | 228 | There are actually three categories of file objects: raw binary files, |
| 229 | buffered binary files and text files. Their interfaces are defined in the |
| 230 | :mod:`io` module. The canonical way to create a file object is by using |
| 231 | the :func:`open` function. |
Antoine Pitrou | 0b65b0f | 2010-09-15 09:58:26 +0000 | [diff] [blame] | 232 | |
| 233 | file-like object |
| 234 | A synonym for :term:`file object`. |
| 235 | |
Brett Cannon | 51d4aab | 2009-01-25 04:21:39 +0000 | [diff] [blame] | 236 | finder |
| 237 | An object that tries to find the :term:`loader` for a module. It must |
Barry Warsaw | d7d2194 | 2012-07-29 16:36:17 -0400 | [diff] [blame] | 238 | implement either a method named :meth:`find_loader` or a method named |
| 239 | :meth:`find_module`. See :pep:`302` and :pep:`420` for details and |
| 240 | :class:`importlib.abc.Finder` for an :term:`abstract base class`. |
Brett Cannon | 51d4aab | 2009-01-25 04:21:39 +0000 | [diff] [blame] | 241 | |
Benjamin Peterson | 2d71822 | 2008-11-21 00:25:02 +0000 | [diff] [blame] | 242 | floor division |
Raymond Hettinger | f37ca3c | 2010-09-01 22:11:53 +0000 | [diff] [blame] | 243 | Mathematical division that rounds down to nearest integer. The floor |
| 244 | division operator is ``//``. For example, the expression ``11 // 4`` |
| 245 | evaluates to ``2`` in contrast to the ``2.75`` returned by float true |
| 246 | division. Note that ``(-11) // 4`` is ``-3`` because that is ``-2.75`` |
| 247 | rounded *downward*. See :pep:`238`. |
Benjamin Peterson | 2d71822 | 2008-11-21 00:25:02 +0000 | [diff] [blame] | 248 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 249 | function |
| 250 | A series of statements which returns some value to a caller. It can also |
Chris Jerdonek | b430994 | 2012-12-25 14:54:44 -0800 | [diff] [blame] | 251 | be passed zero or more :term:`arguments <argument>` which may be used in |
| 252 | the execution of the body. See also :term:`parameter`, :term:`method`, |
| 253 | and the :ref:`function` section. |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 254 | |
R David Murray | 25cd091 | 2013-05-06 12:58:16 -0400 | [diff] [blame] | 255 | function annotation |
| 256 | An arbitrary metadata value associated with a function parameter or return |
| 257 | value. Its syntax is explained in section :ref:`function`. Annotations |
| 258 | may be accessed via the :attr:`__annotations__` special attribute of a |
| 259 | function object. |
| 260 | |
| 261 | Python itself does not assign any particular meaning to function |
| 262 | annotations. They are intended to be interpreted by third-party libraries |
| 263 | or tools. See :pep:`3107`, which describes some of their potential uses. |
| 264 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 265 | __future__ |
Raymond Hettinger | f37ca3c | 2010-09-01 22:11:53 +0000 | [diff] [blame] | 266 | A pseudo-module which programmers can use to enable new language features |
Benjamin Peterson | 2d71822 | 2008-11-21 00:25:02 +0000 | [diff] [blame] | 267 | which are not compatible with the current interpreter. |
| 268 | |
| 269 | By importing the :mod:`__future__` module and evaluating its variables, |
| 270 | you can see when a new feature was first added to the language and when it |
| 271 | becomes the default:: |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 272 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 273 | >>> import __future__ |
| 274 | >>> __future__.division |
| 275 | _Feature((2, 2, 0, 'alpha', 2), (3, 0, 0, 'alpha', 0), 8192) |
| 276 | |
| 277 | garbage collection |
| 278 | The process of freeing memory when it is not used anymore. Python |
| 279 | performs garbage collection via reference counting and a cyclic garbage |
| 280 | collector that is able to detect and break reference cycles. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 281 | |
Benjamin Peterson | 08bf91c | 2010-04-11 16:12:57 +0000 | [diff] [blame] | 282 | .. index:: single: generator |
| 283 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 284 | generator |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 285 | A function which returns an iterator. It looks like a normal function |
Raymond Hettinger | f37ca3c | 2010-09-01 22:11:53 +0000 | [diff] [blame] | 286 | except that it contains :keyword:`yield` statements for producing a series |
| 287 | a values usable in a for-loop or that can be retrieved one at a time with |
| 288 | the :func:`next` function. Each :keyword:`yield` temporarily suspends |
| 289 | processing, remembering the location execution state (including local |
| 290 | variables and pending try-statements). When the generator resumes, it |
| 291 | picks-up where it left-off (in contrast to functions which start fresh on |
Éric Araujo | e0854f9 | 2011-05-27 04:36:52 +0200 | [diff] [blame] | 292 | every invocation). |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 293 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 294 | .. index:: single: generator expression |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 295 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 296 | generator expression |
Benjamin Peterson | 08bf91c | 2010-04-11 16:12:57 +0000 | [diff] [blame] | 297 | An expression that returns an iterator. It looks like a normal expression |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 298 | followed by a :keyword:`for` expression defining a loop variable, range, |
| 299 | and an optional :keyword:`if` expression. The combined expression |
| 300 | generates values for an enclosing function:: |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 301 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 302 | >>> sum(i*i for i in range(10)) # sum of squares 0, 1, 4, ... 81 |
| 303 | 285 |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 304 | |
Łukasz Langa | fdcf2b7 | 2013-06-07 22:54:03 +0200 | [diff] [blame] | 305 | generic function |
| 306 | A function composed of multiple functions implementing the same operation |
| 307 | for different types. Which implementation should be used during a call is |
| 308 | determined by the dispatch algorithm. |
| 309 | |
| 310 | See also the :term:`single dispatch` glossary entry, the |
| 311 | :func:`functools.singledispatch` decorator, and :pep:`443`. |
| 312 | |
| 313 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 314 | GIL |
| 315 | See :term:`global interpreter lock`. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 316 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 317 | global interpreter lock |
Antoine Pitrou | 0034281 | 2011-01-06 16:31:28 +0000 | [diff] [blame] | 318 | The mechanism used by the :term:`CPython` interpreter to assure that |
| 319 | only one thread executes Python :term:`bytecode` at a time. |
| 320 | This simplifies the CPython implementation by making the object model |
| 321 | (including critical built-in types such as :class:`dict`) implicitly |
| 322 | safe against concurrent access. Locking the entire interpreter |
| 323 | makes it easier for the interpreter to be multi-threaded, at the |
| 324 | expense of much of the parallelism afforded by multi-processor |
| 325 | machines. |
| 326 | |
| 327 | However, some extension modules, either standard or third-party, |
| 328 | are designed so as to release the GIL when doing computationally-intensive |
| 329 | tasks such as compression or hashing. Also, the GIL is always released |
| 330 | when doing I/O. |
| 331 | |
| 332 | Past efforts to create a "free-threaded" interpreter (one which locks |
| 333 | shared data at a much finer granularity) have not been successful |
| 334 | because performance suffered in the common single-processor case. It |
| 335 | is believed that overcoming this performance issue would make the |
| 336 | implementation much more complicated and therefore costlier to maintain. |
Guido van Rossum | 2cc30da | 2007-11-02 23:46:40 +0000 | [diff] [blame] | 337 | |
| 338 | hashable |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 339 | An object is *hashable* if it has a hash value which never changes during |
Guido van Rossum | 2cc30da | 2007-11-02 23:46:40 +0000 | [diff] [blame] | 340 | its lifetime (it needs a :meth:`__hash__` method), and can be compared to |
Georg Brandl | 05f5ab7 | 2008-09-24 09:11:47 +0000 | [diff] [blame] | 341 | other objects (it needs an :meth:`__eq__` method). Hashable objects which |
| 342 | compare equal must have the same hash value. |
Guido van Rossum | 2cc30da | 2007-11-02 23:46:40 +0000 | [diff] [blame] | 343 | |
| 344 | Hashability makes an object usable as a dictionary key and a set member, |
| 345 | because these data structures use the hash value internally. |
| 346 | |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 347 | All of Python's immutable built-in objects are hashable, while no mutable |
| 348 | containers (such as lists or dictionaries) are. Objects which are |
Guido van Rossum | 2cc30da | 2007-11-02 23:46:40 +0000 | [diff] [blame] | 349 | instances of user-defined classes are hashable by default; they all |
Ezio Melotti | 188ad85 | 2013-02-01 05:18:44 +0200 | [diff] [blame] | 350 | compare unequal (except with themselves), and their hash value is their |
| 351 | :func:`id`. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 352 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 353 | IDLE |
| 354 | An Integrated Development Environment for Python. IDLE is a basic editor |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 355 | and interpreter environment which ships with the standard distribution of |
Raymond Hettinger | f37ca3c | 2010-09-01 22:11:53 +0000 | [diff] [blame] | 356 | Python. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 357 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 358 | immutable |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 359 | An object with a fixed value. Immutable objects include numbers, strings and |
| 360 | tuples. Such an object cannot be altered. A new object has to |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 361 | be created if a different value has to be stored. They play an important |
| 362 | role in places where a constant hash value is needed, for example as a key |
| 363 | in a dictionary. |
Benjamin Peterson | 2d71822 | 2008-11-21 00:25:02 +0000 | [diff] [blame] | 364 | |
Barry Warsaw | dadebab | 2012-07-31 16:03:09 -0400 | [diff] [blame] | 365 | import path |
| 366 | A list of locations (or :term:`path entries <path entry>`) that are |
Nick Coghlan | 1685db0 | 2012-08-20 13:49:08 +1000 | [diff] [blame] | 367 | searched by the :term:`path based finder` for modules to import. During |
Barry Warsaw | dadebab | 2012-07-31 16:03:09 -0400 | [diff] [blame] | 368 | import, this list of locations usually comes from :data:`sys.path`, but |
| 369 | for subpackages it may also come from the parent package's ``__path__`` |
| 370 | attribute. |
| 371 | |
Barry Warsaw | d7d2194 | 2012-07-29 16:36:17 -0400 | [diff] [blame] | 372 | importing |
| 373 | The process by which Python code in one module is made available to |
| 374 | Python code in another module. |
| 375 | |
Brett Cannon | 51d4aab | 2009-01-25 04:21:39 +0000 | [diff] [blame] | 376 | importer |
| 377 | An object that both finds and loads a module; both a |
| 378 | :term:`finder` and :term:`loader` object. |
| 379 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 380 | interactive |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 381 | Python has an interactive interpreter which means you can enter |
| 382 | statements and expressions at the interpreter prompt, immediately |
| 383 | execute them and see their results. Just launch ``python`` with no |
| 384 | arguments (possibly by selecting it from your computer's main |
| 385 | menu). It is a very powerful way to test out new ideas or inspect |
| 386 | modules and packages (remember ``help(x)``). |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 387 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 388 | interpreted |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 389 | Python is an interpreted language, as opposed to a compiled one, |
| 390 | though the distinction can be blurry because of the presence of the |
| 391 | bytecode compiler. This means that source files can be run directly |
| 392 | without explicitly creating an executable which is then run. |
| 393 | Interpreted languages typically have a shorter development/debug cycle |
| 394 | than compiled ones, though their programs generally also run more |
| 395 | slowly. See also :term:`interactive`. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 396 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 397 | iterable |
Ezio Melotti | d581fff | 2013-01-02 22:29:09 +0200 | [diff] [blame] | 398 | An object capable of returning its members one at a time. Examples of |
| 399 | iterables include all sequence types (such as :class:`list`, :class:`str`, |
| 400 | and :class:`tuple`) and some non-sequence types like :class:`dict`, |
| 401 | :term:`file objects <file object>`, and objects of any classes you define |
| 402 | with an :meth:`__iter__` or :meth:`__getitem__` method. Iterables can be |
| 403 | used in a :keyword:`for` loop and in many other places where a sequence is |
| 404 | needed (:func:`zip`, :func:`map`, ...). When an iterable object is passed |
| 405 | as an argument to the built-in function :func:`iter`, it returns an |
| 406 | iterator for the object. This iterator is good for one pass over the set |
| 407 | of values. When using iterables, it is usually not necessary to call |
| 408 | :func:`iter` or deal with iterator objects yourself. The ``for`` |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 409 | statement does that automatically for you, creating a temporary unnamed |
| 410 | variable to hold the iterator for the duration of the loop. See also |
| 411 | :term:`iterator`, :term:`sequence`, and :term:`generator`. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 412 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 413 | iterator |
| 414 | An object representing a stream of data. Repeated calls to the iterator's |
Ezio Melotti | 7fa8222 | 2012-10-12 13:42:08 +0300 | [diff] [blame] | 415 | :meth:`~iterator.__next__` method (or passing it to the built-in function |
Georg Brandl | b30f330 | 2011-01-06 09:23:56 +0000 | [diff] [blame] | 416 | :func:`next`) return successive items in the stream. When no more data |
| 417 | are available a :exc:`StopIteration` exception is raised instead. At this |
Benjamin Peterson | e7c78b2 | 2008-07-03 20:28:26 +0000 | [diff] [blame] | 418 | point, the iterator object is exhausted and any further calls to its |
Georg Brandl | b30f330 | 2011-01-06 09:23:56 +0000 | [diff] [blame] | 419 | :meth:`__next__` method just raise :exc:`StopIteration` again. Iterators |
| 420 | are required to have an :meth:`__iter__` method that returns the iterator |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 421 | object itself so every iterator is also iterable and may be used in most |
| 422 | places where other iterables are accepted. One notable exception is code |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 423 | which attempts multiple iteration passes. A container object (such as a |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 424 | :class:`list`) produces a fresh new iterator each time you pass it to the |
| 425 | :func:`iter` function or use it in a :keyword:`for` loop. Attempting this |
| 426 | with an iterator will just return the same exhausted iterator object used |
| 427 | in the previous iteration pass, making it appear like an empty container. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 428 | |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 429 | More information can be found in :ref:`typeiter`. |
| 430 | |
Georg Brandl | c275e15 | 2010-11-05 07:10:41 +0000 | [diff] [blame] | 431 | key function |
| 432 | A key function or collation function is a callable that returns a value |
| 433 | used for sorting or ordering. For example, :func:`locale.strxfrm` is |
| 434 | used to produce a sort key that is aware of locale specific sort |
| 435 | conventions. |
| 436 | |
| 437 | A number of tools in Python accept key functions to control how elements |
| 438 | are ordered or grouped. They include :func:`min`, :func:`max`, |
| 439 | :func:`sorted`, :meth:`list.sort`, :func:`heapq.nsmallest`, |
| 440 | :func:`heapq.nlargest`, and :func:`itertools.groupby`. |
| 441 | |
| 442 | There are several ways to create a key function. For example. the |
| 443 | :meth:`str.lower` method can serve as a key function for case insensitive |
| 444 | sorts. Alternatively, an ad-hoc key function can be built from a |
| 445 | :keyword:`lambda` expression such as ``lambda r: (r[0], r[2])``. Also, |
Sandro Tosi | 165a2c2 | 2012-04-01 01:50:00 +0200 | [diff] [blame] | 446 | the :mod:`operator` module provides three key function constructors: |
Georg Brandl | c275e15 | 2010-11-05 07:10:41 +0000 | [diff] [blame] | 447 | :func:`~operator.attrgetter`, :func:`~operator.itemgetter`, and |
| 448 | :func:`~operator.methodcaller`. See the :ref:`Sorting HOW TO |
| 449 | <sortinghowto>` for examples of how to create and use key functions. |
| 450 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 451 | keyword argument |
Chris Jerdonek | c2a7fd6 | 2012-11-28 02:29:33 -0800 | [diff] [blame] | 452 | See :term:`argument`. |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 453 | |
| 454 | lambda |
| 455 | An anonymous inline function consisting of a single :term:`expression` |
| 456 | which is evaluated when the function is called. The syntax to create |
| 457 | a lambda function is ``lambda [arguments]: expression`` |
| 458 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 459 | LBYL |
| 460 | Look before you leap. This coding style explicitly tests for |
| 461 | pre-conditions before making calls or lookups. This style contrasts with |
| 462 | the :term:`EAFP` approach and is characterized by the presence of many |
| 463 | :keyword:`if` statements. |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 464 | |
Raymond Hettinger | 09f4414 | 2010-12-17 20:19:50 +0000 | [diff] [blame] | 465 | In a multi-threaded environment, the LBYL approach can risk introducing a |
| 466 | race condition between "the looking" and "the leaping". For example, the |
| 467 | code, ``if key in mapping: return mapping[key]`` can fail if another |
| 468 | thread removes *key* from *mapping* after the test, but before the lookup. |
| 469 | This issue can be solved with locks or by using the EAFP approach. |
| 470 | |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 471 | list |
| 472 | A built-in Python :term:`sequence`. Despite its name it is more akin |
| 473 | to an array in other languages than to a linked list since access to |
| 474 | elements are O(1). |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 475 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 476 | list comprehension |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 477 | A compact way to process all or part of the elements in a sequence and |
Georg Brandl | ede6c2a | 2010-01-05 10:22:04 +0000 | [diff] [blame] | 478 | return a list with the results. ``result = ['{:#04x}'.format(x) for x in |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 479 | range(256) if x % 2 == 0]`` generates a list of strings containing |
| 480 | even hex numbers (0x..) in the range from 0 to 255. The :keyword:`if` |
| 481 | clause is optional. If omitted, all elements in ``range(256)`` are |
| 482 | processed. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 483 | |
Brett Cannon | 51d4aab | 2009-01-25 04:21:39 +0000 | [diff] [blame] | 484 | loader |
| 485 | An object that loads a module. It must define a method named |
| 486 | :meth:`load_module`. A loader is typically returned by a |
Brett Cannon | e43b060 | 2009-03-21 03:11:16 +0000 | [diff] [blame] | 487 | :term:`finder`. See :pep:`302` for details and |
| 488 | :class:`importlib.abc.Loader` for an :term:`abstract base class`. |
Brett Cannon | 51d4aab | 2009-01-25 04:21:39 +0000 | [diff] [blame] | 489 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 490 | mapping |
Raymond Hettinger | e3ee66f | 2011-01-08 23:44:37 +0000 | [diff] [blame] | 491 | A container object that supports arbitrary key lookups and implements the |
Éric Araujo | b8edbdf | 2011-09-01 05:57:12 +0200 | [diff] [blame] | 492 | methods specified in the :class:`~collections.abc.Mapping` or |
| 493 | :class:`~collections.abc.MutableMapping` |
Éric Araujo | fa088db | 2011-06-04 18:42:38 +0200 | [diff] [blame] | 494 | :ref:`abstract base classes <collections-abstract-base-classes>`. Examples |
| 495 | include :class:`dict`, :class:`collections.defaultdict`, |
Raymond Hettinger | e3ee66f | 2011-01-08 23:44:37 +0000 | [diff] [blame] | 496 | :class:`collections.OrderedDict` and :class:`collections.Counter`. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 497 | |
Barry Warsaw | d7d2194 | 2012-07-29 16:36:17 -0400 | [diff] [blame] | 498 | meta path finder |
| 499 | A finder returned by a search of :data:`sys.meta_path`. Meta path |
Barry Warsaw | dadebab | 2012-07-31 16:03:09 -0400 | [diff] [blame] | 500 | finders are related to, but different from :term:`path entry finders |
| 501 | <path entry finder>`. |
Barry Warsaw | d7d2194 | 2012-07-29 16:36:17 -0400 | [diff] [blame] | 502 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 503 | metaclass |
| 504 | The class of a class. Class definitions create a class name, a class |
| 505 | dictionary, and a list of base classes. The metaclass is responsible for |
| 506 | taking those three arguments and creating the class. Most object oriented |
| 507 | programming languages provide a default implementation. What makes Python |
| 508 | special is that it is possible to create custom metaclasses. Most users |
| 509 | never need this tool, but when the need arises, metaclasses can provide |
| 510 | powerful, elegant solutions. They have been used for logging attribute |
| 511 | access, adding thread-safety, tracking object creation, implementing |
| 512 | singletons, and many other tasks. |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 513 | |
| 514 | More information can be found in :ref:`metaclasses`. |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 515 | |
| 516 | method |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 517 | A function which is defined inside a class body. If called as an attribute |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 518 | of an instance of that class, the method will get the instance object as |
| 519 | its first :term:`argument` (which is usually called ``self``). |
| 520 | See :term:`function` and :term:`nested scope`. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 521 | |
Michael Foord | 95fc51d | 2010-11-20 15:07:30 +0000 | [diff] [blame] | 522 | method resolution order |
| 523 | Method Resolution Order is the order in which base classes are searched |
| 524 | for a member during lookup. See `The Python 2.3 Method Resolution Order |
| 525 | <http://www.python.org/download/releases/2.3/mro/>`_. |
| 526 | |
Barry Warsaw | d7d2194 | 2012-07-29 16:36:17 -0400 | [diff] [blame] | 527 | module |
| 528 | An object that serves as an organizational unit of Python code. Modules |
Barry Warsaw | c1e721b | 2012-07-30 16:24:12 -0400 | [diff] [blame] | 529 | have a namespace containing arbitrary Python objects. Modules are loaded |
Barry Warsaw | d7d2194 | 2012-07-29 16:36:17 -0400 | [diff] [blame] | 530 | into Python by the process of :term:`importing`. |
| 531 | |
Michael Foord | 95fc51d | 2010-11-20 15:07:30 +0000 | [diff] [blame] | 532 | MRO |
| 533 | See :term:`method resolution order`. |
| 534 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 535 | mutable |
| 536 | Mutable objects can change their value but keep their :func:`id`. See |
| 537 | also :term:`immutable`. |
Christian Heimes | 25bb783 | 2008-01-11 16:17:00 +0000 | [diff] [blame] | 538 | |
| 539 | named tuple |
Raymond Hettinger | d04fa31 | 2009-02-04 19:45:13 +0000 | [diff] [blame] | 540 | Any tuple-like class whose indexable elements are also accessible using |
Christian Heimes | d32ed6f | 2008-01-14 18:49:24 +0000 | [diff] [blame] | 541 | named attributes (for example, :func:`time.localtime` returns a |
| 542 | tuple-like object where the *year* is accessible either with an |
| 543 | index such as ``t[0]`` or with a named attribute like ``t.tm_year``). |
| 544 | |
| 545 | A named tuple can be a built-in type such as :class:`time.struct_time`, |
| 546 | or it can be created with a regular class definition. A full featured |
| 547 | named tuple can also be created with the factory function |
| 548 | :func:`collections.namedtuple`. The latter approach automatically |
| 549 | provides extra features such as a self-documenting representation like |
| 550 | ``Employee(name='jones', title='programmer')``. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 551 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 552 | namespace |
| 553 | The place where a variable is stored. Namespaces are implemented as |
Georg Brandl | 22b3431 | 2009-07-26 14:54:51 +0000 | [diff] [blame] | 554 | dictionaries. There are the local, global and built-in namespaces as well |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 555 | as nested namespaces in objects (in methods). Namespaces support |
| 556 | modularity by preventing naming conflicts. For instance, the functions |
Georg Brandl | 1a3284e | 2007-12-02 09:40:06 +0000 | [diff] [blame] | 557 | :func:`builtins.open` and :func:`os.open` are distinguished by their |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 558 | namespaces. Namespaces also aid readability and maintainability by making |
| 559 | it clear which module implements a function. For instance, writing |
Éric Araujo | 7af8ebb | 2011-09-01 03:20:13 +0200 | [diff] [blame] | 560 | :func:`random.seed` or :func:`itertools.islice` makes it clear that those |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 561 | functions are implemented by the :mod:`random` and :mod:`itertools` |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 562 | modules, respectively. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 563 | |
Barry Warsaw | d7d2194 | 2012-07-29 16:36:17 -0400 | [diff] [blame] | 564 | namespace package |
| 565 | A :pep:`420` :term:`package` which serves only as a container for |
| 566 | subpackages. Namespace packages may have no physical representation, |
| 567 | and specifically are not like a :term:`regular package` because they |
| 568 | have no ``__init__.py`` file. |
| 569 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 570 | nested scope |
| 571 | The ability to refer to a variable in an enclosing definition. For |
| 572 | instance, a function defined inside another function can refer to |
Benjamin Peterson | 927ccd2 | 2010-06-29 18:36:39 +0000 | [diff] [blame] | 573 | variables in the outer function. Note that nested scopes by default work |
| 574 | only for reference and not for assignment. Local variables both read and |
| 575 | write in the innermost scope. Likewise, global variables read and write |
| 576 | to the global namespace. The :keyword:`nonlocal` allows writing to outer |
| 577 | scopes. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 578 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 579 | new-style class |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 580 | Old name for the flavor of classes now used for all class objects. In |
| 581 | earlier Python versions, only new-style classes could use Python's newer, |
| 582 | versatile features like :attr:`__slots__`, descriptors, properties, |
| 583 | :meth:`__getattribute__`, class methods, and static methods. |
Georg Brandl | 9afde1c | 2007-11-01 20:32:30 +0000 | [diff] [blame] | 584 | |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 585 | object |
| 586 | Any data with state (attributes or value) and defined behavior |
| 587 | (methods). Also the ultimate base class of any :term:`new-style |
| 588 | class`. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 589 | |
Barry Warsaw | d7d2194 | 2012-07-29 16:36:17 -0400 | [diff] [blame] | 590 | package |
| 591 | A Python module which can contain submodules or recursively, |
| 592 | subpackages. Technically, a package is a Python module with an |
| 593 | ``__path__`` attribute. |
| 594 | |
Chris Jerdonek | c2a7fd6 | 2012-11-28 02:29:33 -0800 | [diff] [blame] | 595 | parameter |
| 596 | A named entity in a :term:`function` (or method) definition that |
| 597 | specifies an :term:`argument` (or in some cases, arguments) that the |
| 598 | function can accept. There are five types of parameters: |
| 599 | |
| 600 | * :dfn:`positional-or-keyword`: specifies an argument that can be passed |
| 601 | either :term:`positionally <argument>` or as a :term:`keyword argument |
| 602 | <argument>`. This is the default kind of parameter, for example *foo* |
| 603 | and *bar* in the following:: |
| 604 | |
| 605 | def func(foo, bar=None): ... |
| 606 | |
| 607 | * :dfn:`positional-only`: specifies an argument that can be supplied only |
| 608 | by position. Python has no syntax for defining positional-only |
| 609 | parameters. However, some built-in functions have positional-only |
| 610 | parameters (e.g. :func:`abs`). |
| 611 | |
| 612 | * :dfn:`keyword-only`: specifies an argument that can be supplied only |
| 613 | by keyword. Keyword-only parameters can be defined by including a |
| 614 | single var-positional parameter or bare ``*`` in the parameter list |
| 615 | of the function definition before them, for example *kw_only1* and |
| 616 | *kw_only2* in the following:: |
| 617 | |
| 618 | def func(arg, *, kw_only1, kw_only2): ... |
| 619 | |
| 620 | * :dfn:`var-positional`: specifies that an arbitrary sequence of |
| 621 | positional arguments can be provided (in addition to any positional |
| 622 | arguments already accepted by other parameters). Such a parameter can |
| 623 | be defined by prepending the parameter name with ``*``, for example |
| 624 | *args* in the following:: |
| 625 | |
| 626 | def func(*args, **kwargs): ... |
| 627 | |
| 628 | * :dfn:`var-keyword`: specifies that arbitrarily many keyword arguments |
| 629 | can be provided (in addition to any keyword arguments already accepted |
| 630 | by other parameters). Such a parameter can be defined by prepending |
| 631 | the parameter name with ``**``, for example *kwargs* in the example |
| 632 | above. |
| 633 | |
| 634 | Parameters can specify both optional and required arguments, as well as |
| 635 | default values for some optional arguments. |
| 636 | |
| 637 | See also the :term:`argument` glossary entry, the FAQ question on |
| 638 | :ref:`the difference between arguments and parameters |
| 639 | <faq-argument-vs-parameter>`, the :class:`inspect.Parameter` class, the |
| 640 | :ref:`function` section, and :pep:`362`. |
| 641 | |
Barry Warsaw | dadebab | 2012-07-31 16:03:09 -0400 | [diff] [blame] | 642 | path entry |
| 643 | A single location on the :term:`import path` which the :term:`path |
Nick Coghlan | 1685db0 | 2012-08-20 13:49:08 +1000 | [diff] [blame] | 644 | based finder` consults to find modules for importing. |
Barry Warsaw | dadebab | 2012-07-31 16:03:09 -0400 | [diff] [blame] | 645 | |
| 646 | path entry finder |
| 647 | A :term:`finder` returned by a callable on :data:`sys.path_hooks` |
| 648 | (i.e. a :term:`path entry hook`) which knows how to locate modules given |
| 649 | a :term:`path entry`. |
| 650 | |
| 651 | path entry hook |
| 652 | A callable on the :data:`sys.path_hook` list which returns a :term:`path |
| 653 | entry finder` if it knows how to find modules on a specific :term:`path |
| 654 | entry`. |
| 655 | |
Nick Coghlan | 1685db0 | 2012-08-20 13:49:08 +1000 | [diff] [blame] | 656 | path based finder |
Barry Warsaw | dadebab | 2012-07-31 16:03:09 -0400 | [diff] [blame] | 657 | One of the default :term:`meta path finders <meta path finder>` which |
| 658 | searches an :term:`import path` for modules. |
Barry Warsaw | d7d2194 | 2012-07-29 16:36:17 -0400 | [diff] [blame] | 659 | |
| 660 | portion |
| 661 | A set of files in a single directory (possibly stored in a zip file) |
| 662 | that contribute to a namespace package, as defined in :pep:`420`. |
| 663 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 664 | positional argument |
Chris Jerdonek | c2a7fd6 | 2012-11-28 02:29:33 -0800 | [diff] [blame] | 665 | See :term:`argument`. |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 666 | |
Eli Bendersky | 6bdb650 | 2012-03-30 10:52:25 +0300 | [diff] [blame] | 667 | provisional package |
Barry Warsaw | d7d2194 | 2012-07-29 16:36:17 -0400 | [diff] [blame] | 668 | A provisional package is one which has been deliberately excluded from |
| 669 | the standard library's backwards compatibility guarantees. While major |
Eli Bendersky | 6bdb650 | 2012-03-30 10:52:25 +0300 | [diff] [blame] | 670 | changes to such packages are not expected, as long as they are marked |
| 671 | provisional, backwards incompatible changes (up to and including removal |
| 672 | of the package) may occur if deemed necessary by core developers. Such |
| 673 | changes will not be made gratuitously -- they will occur only if serious |
| 674 | flaws are uncovered that were missed prior to the inclusion of the |
| 675 | package. |
| 676 | |
Barry Warsaw | d7d2194 | 2012-07-29 16:36:17 -0400 | [diff] [blame] | 677 | This process allows the standard library to continue to evolve over |
| 678 | time, without locking in problematic design errors for extended periods |
| 679 | of time. See :pep:`411` for more details. |
Eli Bendersky | 6bdb650 | 2012-03-30 10:52:25 +0300 | [diff] [blame] | 680 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 681 | Python 3000 |
Barry Warsaw | d7d2194 | 2012-07-29 16:36:17 -0400 | [diff] [blame] | 682 | Nickname for the Python 3.x release line (coined long ago when the |
| 683 | release of version 3 was something in the distant future.) This is also |
Benjamin Peterson | 1e2f050 | 2008-05-26 12:52:02 +0000 | [diff] [blame] | 684 | abbreviated "Py3k". |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 685 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 686 | Pythonic |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 687 | An idea or piece of code which closely follows the most common idioms |
| 688 | of the Python language, rather than implementing code using concepts |
| 689 | common to other languages. For example, a common idiom in Python is |
| 690 | to loop over all elements of an iterable using a :keyword:`for` |
| 691 | statement. Many other languages don't have this type of construct, so |
| 692 | people unfamiliar with Python sometimes use a numerical counter instead:: |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 693 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 694 | for i in range(len(food)): |
Georg Brandl | a09ca38 | 2007-12-02 18:20:12 +0000 | [diff] [blame] | 695 | print(food[i]) |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 696 | |
| 697 | As opposed to the cleaner, Pythonic method:: |
| 698 | |
| 699 | for piece in food: |
Georg Brandl | a09ca38 | 2007-12-02 18:20:12 +0000 | [diff] [blame] | 700 | print(piece) |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 701 | |
Antoine Pitrou | 86a36b5 | 2011-11-25 18:56:07 +0100 | [diff] [blame] | 702 | qualified name |
| 703 | A dotted name showing the "path" from a module's global scope to a |
| 704 | class, function or method defined in that module, as defined in |
| 705 | :pep:`3155`. For top-level functions and classes, the qualified name |
| 706 | is the same as the object's name:: |
| 707 | |
| 708 | >>> class C: |
| 709 | ... class D: |
| 710 | ... def meth(self): |
| 711 | ... pass |
| 712 | ... |
| 713 | >>> C.__qualname__ |
| 714 | 'C' |
| 715 | >>> C.D.__qualname__ |
| 716 | 'C.D' |
| 717 | >>> C.D.meth.__qualname__ |
| 718 | 'C.D.meth' |
| 719 | |
Barry Warsaw | d7d2194 | 2012-07-29 16:36:17 -0400 | [diff] [blame] | 720 | When used to refer to modules, the *fully qualified name* means the |
| 721 | entire dotted path to the module, including any parent packages, |
| 722 | e.g. ``email.mime.text``:: |
| 723 | |
| 724 | >>> import email.mime.text |
| 725 | >>> email.mime.text.__name__ |
| 726 | 'email.mime.text' |
| 727 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 728 | reference count |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 729 | The number of references to an object. When the reference count of an |
| 730 | object drops to zero, it is deallocated. Reference counting is |
| 731 | generally not visible to Python code, but it is a key element of the |
| 732 | :term:`CPython` implementation. The :mod:`sys` module defines a |
Georg Brandl | ede6c2a | 2010-01-05 10:22:04 +0000 | [diff] [blame] | 733 | :func:`~sys.getrefcount` function that programmers can call to return the |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 734 | reference count for a particular object. |
| 735 | |
Barry Warsaw | d7d2194 | 2012-07-29 16:36:17 -0400 | [diff] [blame] | 736 | regular package |
| 737 | A traditional :term:`package`, such as a directory containing an |
| 738 | ``__init__.py`` file. |
| 739 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 740 | __slots__ |
Georg Brandl | 85eb8c1 | 2007-08-31 16:33:38 +0000 | [diff] [blame] | 741 | A declaration inside a class that saves memory by pre-declaring space for |
| 742 | instance attributes and eliminating instance dictionaries. Though |
| 743 | popular, the technique is somewhat tricky to get right and is best |
| 744 | reserved for rare cases where there are large numbers of instances in a |
| 745 | memory-critical application. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 746 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 747 | sequence |
| 748 | An :term:`iterable` which supports efficient element access using integer |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 749 | indices via the :meth:`__getitem__` special method and defines a |
Andrew Svetlov | 8cf1cc4 | 2012-10-05 13:26:10 +0300 | [diff] [blame] | 750 | :meth:`__len__` method that returns the length of the sequence. |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 751 | Some built-in sequence types are :class:`list`, :class:`str`, |
Georg Brandl | 2ae8ac2 | 2009-02-05 10:40:48 +0000 | [diff] [blame] | 752 | :class:`tuple`, and :class:`bytes`. Note that :class:`dict` also |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 753 | supports :meth:`__getitem__` and :meth:`__len__`, but is considered a |
| 754 | mapping rather than a sequence because the lookups use arbitrary |
| 755 | :term:`immutable` keys rather than integers. |
| 756 | |
Łukasz Langa | fdcf2b7 | 2013-06-07 22:54:03 +0200 | [diff] [blame] | 757 | single dispatch |
| 758 | A form of :term:`generic function` dispatch where the implementation is |
| 759 | chosen based on the type of a single argument. |
| 760 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 761 | slice |
Georg Brandl | c6fe37b | 2007-12-03 21:07:25 +0000 | [diff] [blame] | 762 | An object usually containing a portion of a :term:`sequence`. A slice is |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 763 | created using the subscript notation, ``[]`` with colons between numbers |
| 764 | when several are given, such as in ``variable_name[1:3:5]``. The bracket |
Georg Brandl | a09ca38 | 2007-12-02 18:20:12 +0000 | [diff] [blame] | 765 | (subscript) notation uses :class:`slice` objects internally. |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 766 | |
Georg Brandl | af265f4 | 2008-12-07 15:06:20 +0000 | [diff] [blame] | 767 | special method |
| 768 | A method that is called implicitly by Python to execute a certain |
| 769 | operation on a type, such as addition. Such methods have names starting |
| 770 | and ending with double underscores. Special methods are documented in |
| 771 | :ref:`specialnames`. |
| 772 | |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 773 | statement |
| 774 | A statement is part of a suite (a "block" of code). A statement is either |
| 775 | an :term:`expression` or a one of several constructs with a keyword, such |
Georg Brandl | a09ca38 | 2007-12-02 18:20:12 +0000 | [diff] [blame] | 776 | as :keyword:`if`, :keyword:`while` or :keyword:`for`. |
Christian Heimes | d8654cf | 2007-12-02 15:22:16 +0000 | [diff] [blame] | 777 | |
Benjamin Peterson | 82f614b | 2011-04-20 18:27:32 -0500 | [diff] [blame] | 778 | struct sequence |
Florent Xicluna | f8240d6 | 2011-11-11 19:58:53 +0100 | [diff] [blame] | 779 | A tuple with named elements. Struct sequences expose an interface similar |
Benjamin Peterson | 82f614b | 2011-04-20 18:27:32 -0500 | [diff] [blame] | 780 | to :term:`named tuple` in that elements can either be accessed either by |
| 781 | index or as an attribute. However, they do not have any of the named tuple |
| 782 | methods like :meth:`~collections.somenamedtuple._make` or |
| 783 | :meth:`~collections.somenamedtuple._asdict`. Examples of struct sequences |
| 784 | include :data:`sys.float_info` and the return value of :func:`os.stat`. |
| 785 | |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 786 | triple-quoted string |
| 787 | A string which is bound by three instances of either a quotation mark |
| 788 | (") or an apostrophe ('). While they don't provide any functionality |
| 789 | not available with single-quoted strings, they are useful for a number |
| 790 | of reasons. They allow you to include unescaped single and double |
| 791 | quotes within a string and they can span multiple lines without the |
| 792 | use of the continuation character, making them especially useful when |
| 793 | writing docstrings. |
| 794 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 795 | type |
| 796 | The type of a Python object determines what kind of object it is; every |
| 797 | object has a type. An object's type is accessible as its |
| 798 | :attr:`__class__` attribute or can be retrieved with ``type(obj)``. |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 799 | |
R David Murray | 1b00f25 | 2012-08-15 10:43:58 -0400 | [diff] [blame] | 800 | universal newlines |
| 801 | A manner of interpreting text streams in which all of the following are |
| 802 | recognized as ending a line: the Unix end-of-line convention ``'\n'``, |
| 803 | the Windows convention ``'\r\n'``, and the old Macintosh convention |
| 804 | ``'\r'``. See :pep:`278` and :pep:`3116`, as well as |
| 805 | :func:`str.splitlines` for an additional use. |
| 806 | |
Benjamin Peterson | 656aa28 | 2008-11-21 23:22:00 +0000 | [diff] [blame] | 807 | view |
Ezio Melotti | 619de8f | 2009-06-25 18:39:31 +0000 | [diff] [blame] | 808 | The objects returned from :meth:`dict.keys`, :meth:`dict.values`, and |
Benjamin Peterson | 656aa28 | 2008-11-21 23:22:00 +0000 | [diff] [blame] | 809 | :meth:`dict.items` are called dictionary views. They are lazy sequences |
| 810 | that will see changes in the underlying dictionary. To force the |
| 811 | dictionary view to become a full list use ``list(dictview)``. See |
| 812 | :ref:`dict-views`. |
| 813 | |
Benjamin Peterson | 5478b47 | 2008-09-17 22:25:09 +0000 | [diff] [blame] | 814 | virtual machine |
| 815 | A computer defined entirely in software. Python's virtual machine |
| 816 | executes the :term:`bytecode` emitted by the bytecode compiler. |
Georg Brandl | 48310cd | 2009-01-03 21:18:54 +0000 | [diff] [blame] | 817 | |
Guido van Rossum | f10aa98 | 2007-08-17 18:30:38 +0000 | [diff] [blame] | 818 | Zen of Python |
| 819 | Listing of Python design principles and philosophies that are helpful in |
| 820 | understanding and using the language. The listing can be found by typing |
| 821 | "``import this``" at the interactive prompt. |