Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 1 | \section{Built-in Functions} |
| 2 | |
| 3 | The Python interpreter has a number of functions built into it that |
| 4 | are always available. They are listed here in alphabetical order. |
| 5 | |
| 6 | |
| 7 | \renewcommand{\indexsubitem}{(built-in function)} |
| 8 | \begin{funcdesc}{abs}{x} |
| 9 | Return the absolute value of a number. The argument may be a plain |
Guido van Rossum | 921f32c | 1997-06-02 17:21:20 +0000 | [diff] [blame^] | 10 | or long integer or a floating point number. If the argument is a |
| 11 | complex number, its magnitude is returned. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 12 | \end{funcdesc} |
| 13 | |
Guido van Rossum | 0568d5e | 1995-10-08 01:06:46 +0000 | [diff] [blame] | 14 | \begin{funcdesc}{apply}{function\, args\optional{, keywords}} |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 15 | The \var{function} argument must be a callable object (a user-defined or |
| 16 | built-in function or method, or a class object) and the \var{args} |
| 17 | argument must be a tuple. The \var{function} is called with |
| 18 | \var{args} as argument list; the number of arguments is the the length |
| 19 | of the tuple. (This is different from just calling |
| 20 | \code{\var{func}(\var{args})}, since in that case there is always |
| 21 | exactly one argument.) |
Guido van Rossum | 0568d5e | 1995-10-08 01:06:46 +0000 | [diff] [blame] | 22 | If the optional \var{keywords} argument is present, it must be a |
| 23 | dictionary whose keys are strings. It specifies keyword arguments to |
| 24 | be added to the end of the the argument list. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 25 | \end{funcdesc} |
| 26 | |
| 27 | \begin{funcdesc}{chr}{i} |
| 28 | Return a string of one character whose \ASCII{} code is the integer |
| 29 | \var{i}, e.g., \code{chr(97)} returns the string \code{'a'}. This is the |
| 30 | inverse of \code{ord()}. The argument must be in the range [0..255], |
| 31 | inclusive. |
| 32 | \end{funcdesc} |
| 33 | |
| 34 | \begin{funcdesc}{cmp}{x\, y} |
| 35 | Compare the two objects \var{x} and \var{y} and return an integer |
| 36 | according to the outcome. The return value is negative if \code{\var{x} |
| 37 | < \var{y}}, zero if \code{\var{x} == \var{y}} and strictly positive if |
| 38 | \code{\var{x} > \var{y}}. |
| 39 | \end{funcdesc} |
| 40 | |
| 41 | \begin{funcdesc}{coerce}{x\, y} |
| 42 | Return a tuple consisting of the two numeric arguments converted to |
| 43 | a common type, using the same rules as used by arithmetic |
| 44 | operations. |
| 45 | \end{funcdesc} |
| 46 | |
| 47 | \begin{funcdesc}{compile}{string\, filename\, kind} |
| 48 | Compile the \var{string} into a code object. Code objects can be |
Guido van Rossum | 6c4f003 | 1995-03-07 10:14:09 +0000 | [diff] [blame] | 49 | executed by an \code{exec} statement or evaluated by a call to |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 50 | \code{eval()}. The \var{filename} argument should |
| 51 | give the file from which the code was read; pass e.g. \code{'<string>'} |
| 52 | if it wasn't read from a file. The \var{kind} argument specifies |
| 53 | what kind of code must be compiled; it can be \code{'exec'} if |
Guido van Rossum | fb502e9 | 1995-07-07 22:58:28 +0000 | [diff] [blame] | 54 | \var{string} consists of a sequence of statements, \code{'eval'} |
| 55 | if it consists of a single expression, or \code{'single'} if |
| 56 | it consists of a single interactive statement (in the latter case, |
| 57 | expression statements that evaluate to something else than |
| 58 | \code{None} will printed). |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 59 | \end{funcdesc} |
| 60 | |
Guido van Rossum | 1cd26f2 | 1997-04-02 06:04:02 +0000 | [diff] [blame] | 61 | \begin{funcdesc}{complex}{real\optional{, imag}} |
| 62 | Create a complex number with the value \var{real} + \var{imag}*j. |
| 63 | Each argument may be any numeric type (including complex). |
| 64 | If \var{imag} is omitted, it defaults to zero and the function |
| 65 | serves as a numeric conversion function like \code{int}, \code{long} |
| 66 | and \code{float}. |
| 67 | \end{funcdesc} |
| 68 | |
Guido van Rossum | 1efbb0f | 1994-08-16 22:15:11 +0000 | [diff] [blame] | 69 | \begin{funcdesc}{delattr}{object\, name} |
| 70 | This is a relative of \code{setattr}. The arguments are an |
| 71 | object and a string. The string must be the name |
| 72 | of one of the object's attributes. The function deletes |
| 73 | the named attribute, provided the object allows it. For example, |
Guido van Rossum | 6c4f003 | 1995-03-07 10:14:09 +0000 | [diff] [blame] | 74 | \code{delattr(\var{x}, '\var{foobar}')} is equivalent to |
Guido van Rossum | 1efbb0f | 1994-08-16 22:15:11 +0000 | [diff] [blame] | 75 | \code{del \var{x}.\var{foobar}}. |
| 76 | \end{funcdesc} |
| 77 | |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 78 | \begin{funcdesc}{dir}{} |
| 79 | Without arguments, return the list of names in the current local |
| 80 | symbol table. With a module, class or class instance object as |
| 81 | argument (or anything else that has a \code{__dict__} attribute), |
| 82 | returns the list of names in that object's attribute dictionary. |
| 83 | The resulting list is sorted. For example: |
| 84 | |
| 85 | \bcode\begin{verbatim} |
| 86 | >>> import sys |
| 87 | >>> dir() |
| 88 | ['sys'] |
| 89 | >>> dir(sys) |
| 90 | ['argv', 'exit', 'modules', 'path', 'stderr', 'stdin', 'stdout'] |
| 91 | >>> |
| 92 | \end{verbatim}\ecode |
| 93 | \end{funcdesc} |
| 94 | |
| 95 | \begin{funcdesc}{divmod}{a\, b} |
| 96 | Take two numbers as arguments and return a pair of integers |
| 97 | consisting of their integer quotient and remainder. With mixed |
| 98 | operand types, the rules for binary arithmetic operators apply. For |
| 99 | plain and long integers, the result is the same as |
| 100 | \code{(\var{a} / \var{b}, \var{a} \%{} \var{b})}. |
| 101 | For floating point numbers the result is the same as |
| 102 | \code{(math.floor(\var{a} / \var{b}), \var{a} \%{} \var{b})}. |
| 103 | \end{funcdesc} |
| 104 | |
Guido van Rossum | f860162 | 1995-01-10 10:50:24 +0000 | [diff] [blame] | 105 | \begin{funcdesc}{eval}{expression\optional{\, globals\optional{\, locals}}} |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 106 | The arguments are a string and two optional dictionaries. The |
Guido van Rossum | f860162 | 1995-01-10 10:50:24 +0000 | [diff] [blame] | 107 | \var{expression} argument is parsed and evaluated as a Python |
| 108 | expression (technically speaking, a condition list) using the |
| 109 | \var{globals} and \var{locals} dictionaries as global and local name |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 110 | space. If the \var{locals} dictionary is omitted it defaults to |
| 111 | the \var{globals} dictionary. If both dictionaries are omitted, the |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 112 | expression is executed in the environment where \code{eval} is |
Guido van Rossum | f860162 | 1995-01-10 10:50:24 +0000 | [diff] [blame] | 113 | called. The return value is the result of the evaluated expression. |
| 114 | Syntax errors are reported as exceptions. Example: |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 115 | |
| 116 | \bcode\begin{verbatim} |
| 117 | >>> x = 1 |
| 118 | >>> print eval('x+1') |
| 119 | 2 |
| 120 | >>> |
| 121 | \end{verbatim}\ecode |
| 122 | |
| 123 | This function can also be used to execute arbitrary code objects |
Guido van Rossum | 6c4f003 | 1995-03-07 10:14:09 +0000 | [diff] [blame] | 124 | (e.g.\ created by \code{compile()}). In this case pass a code |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 125 | object instead of a string. The code object must have been compiled |
| 126 | passing \code{'eval'} to the \var{kind} argument. |
| 127 | |
Guido van Rossum | 6c4f003 | 1995-03-07 10:14:09 +0000 | [diff] [blame] | 128 | Hints: dynamic execution of statements is supported by the |
Guido van Rossum | f860162 | 1995-01-10 10:50:24 +0000 | [diff] [blame] | 129 | \code{exec} statement. Execution of statements from a file is |
Guido van Rossum | fb502e9 | 1995-07-07 22:58:28 +0000 | [diff] [blame] | 130 | supported by the \code{execfile()} function. The \code{globals()} |
| 131 | and \code{locals()} functions returns the current global and local |
| 132 | dictionary, respectively, which may be useful |
Guido van Rossum | 6c4f003 | 1995-03-07 10:14:09 +0000 | [diff] [blame] | 133 | to pass around for use by \code{eval()} or \code{execfile()}. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 134 | |
| 135 | \end{funcdesc} |
| 136 | |
Guido van Rossum | f860162 | 1995-01-10 10:50:24 +0000 | [diff] [blame] | 137 | \begin{funcdesc}{execfile}{file\optional{\, globals\optional{\, locals}}} |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 138 | This function is similar to the |
Guido van Rossum | f860162 | 1995-01-10 10:50:24 +0000 | [diff] [blame] | 139 | \code{exec} statement, but parses a file instead of a string. It is |
| 140 | different from the \code{import} statement in that it does not use |
Guido van Rossum | 8675115 | 1995-02-28 17:14:32 +0000 | [diff] [blame] | 141 | the module administration --- it reads the file unconditionally and |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 142 | does not create a new module.\footnote{It is used relatively rarely |
| 143 | so does not warrant being made into a statement.} |
Guido van Rossum | f860162 | 1995-01-10 10:50:24 +0000 | [diff] [blame] | 144 | |
| 145 | The arguments are a file name and two optional dictionaries. The |
| 146 | file is parsed and evaluated as a sequence of Python statements |
| 147 | (similarly to a module) using the \var{globals} and \var{locals} |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 148 | dictionaries as global and local name space. If the \var{locals} |
| 149 | dictionary is omitted it defaults to the \var{globals} dictionary. |
Guido van Rossum | f860162 | 1995-01-10 10:50:24 +0000 | [diff] [blame] | 150 | If both dictionaries are omitted, the expression is executed in the |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 151 | environment where \code{execfile()} is called. The return value is |
| 152 | \code{None}. |
Guido van Rossum | f860162 | 1995-01-10 10:50:24 +0000 | [diff] [blame] | 153 | \end{funcdesc} |
| 154 | |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 155 | \begin{funcdesc}{filter}{function\, list} |
| 156 | Construct a list from those elements of \var{list} for which |
| 157 | \var{function} returns true. If \var{list} is a string or a tuple, |
| 158 | the result also has that type; otherwise it is always a list. If |
| 159 | \var{function} is \code{None}, the identity function is assumed, |
Guido van Rossum | 6c4f003 | 1995-03-07 10:14:09 +0000 | [diff] [blame] | 160 | i.e.\ all elements of \var{list} that are false (zero or empty) are |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 161 | removed. |
| 162 | \end{funcdesc} |
| 163 | |
| 164 | \begin{funcdesc}{float}{x} |
Guido van Rossum | 1cd26f2 | 1997-04-02 06:04:02 +0000 | [diff] [blame] | 165 | Convert a string or a number to floating point. If the argument is a |
| 166 | string, it must contain a possibly singed decimal or floating point |
| 167 | number, possibly embedded in whitespace; |
| 168 | this behaves identical to \code{string.atof(\var{x})}. |
| 169 | Otherwise, the argument may be a plain or |
| 170 | long integer or a floating point number, and a floating point number |
| 171 | with the same value (within Python's floating point precision) is |
| 172 | returned. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 173 | \end{funcdesc} |
| 174 | |
| 175 | \begin{funcdesc}{getattr}{object\, name} |
| 176 | The arguments are an object and a string. The string must be the |
| 177 | name |
| 178 | of one of the object's attributes. The result is the value of that |
| 179 | attribute. For example, \code{getattr(\var{x}, '\var{foobar}')} is equivalent to |
| 180 | \code{\var{x}.\var{foobar}}. |
| 181 | \end{funcdesc} |
| 182 | |
Guido van Rossum | fb502e9 | 1995-07-07 22:58:28 +0000 | [diff] [blame] | 183 | \begin{funcdesc}{globals}{} |
| 184 | Return a dictionary representing the current global symbol table. |
| 185 | This is always the dictionary of the current module (inside a |
| 186 | function or method, this is the module where it is defined, not the |
| 187 | module from which it is called). |
| 188 | \end{funcdesc} |
| 189 | |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 190 | \begin{funcdesc}{hasattr}{object\, name} |
| 191 | The arguments are an object and a string. The result is 1 if the |
| 192 | string is the name of one of the object's attributes, 0 if not. |
| 193 | (This is implemented by calling \code{getattr(object, name)} and |
| 194 | seeing whether it raises an exception or not.) |
| 195 | \end{funcdesc} |
| 196 | |
| 197 | \begin{funcdesc}{hash}{object} |
| 198 | Return the hash value of the object (if it has one). Hash values |
| 199 | are 32-bit integers. They are used to quickly compare dictionary |
| 200 | keys during a dictionary lookup. Numeric values that compare equal |
| 201 | have the same hash value (even if they are of different types, e.g. |
| 202 | 1 and 1.0). |
| 203 | \end{funcdesc} |
| 204 | |
| 205 | \begin{funcdesc}{hex}{x} |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 206 | Convert an integer number (of any size) to a hexadecimal string. |
Guido van Rossum | 5cd7520 | 1997-01-14 18:44:23 +0000 | [diff] [blame] | 207 | The result is a valid Python expression. Note: this always yields |
| 208 | an unsigned literal, e.g. on a 32-bit machine, \code{hex(-1)} yields |
| 209 | \code{'0xffffffff'}. When evaluated on a machine with the same |
| 210 | word size, this literal is evaluated as -1; at a different word |
| 211 | size, it may turn up as a large positive number or raise an |
| 212 | \code{OverflowError} exception. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 213 | \end{funcdesc} |
| 214 | |
| 215 | \begin{funcdesc}{id}{object} |
| 216 | Return the `identity' of an object. This is an integer which is |
| 217 | guaranteed to be unique and constant for this object during its |
| 218 | lifetime. (Two objects whose lifetimes are disjunct may have the |
| 219 | same id() value.) (Implementation note: this is the address of the |
| 220 | object.) |
| 221 | \end{funcdesc} |
| 222 | |
Guido van Rossum | 16d6e71 | 1994-08-08 12:30:22 +0000 | [diff] [blame] | 223 | \begin{funcdesc}{input}{\optional{prompt}} |
| 224 | Almost equivalent to \code{eval(raw_input(\var{prompt}))}. Like |
Guido van Rossum | 921f32c | 1997-06-02 17:21:20 +0000 | [diff] [blame^] | 225 | \code{raw_input()}, the \var{prompt} argument is optional, and GNU |
| 226 | readline is used when configured. The difference |
Guido van Rossum | 16d6e71 | 1994-08-08 12:30:22 +0000 | [diff] [blame] | 227 | is that a long input expression may be broken over multiple lines using |
| 228 | the backslash convention. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 229 | \end{funcdesc} |
| 230 | |
Guido van Rossum | 3978d75 | 1997-03-03 16:03:27 +0000 | [diff] [blame] | 231 | \begin{funcdesc}{intern}{string} |
| 232 | Enter \var{string} in the table of ``interned'' strings and return |
| 233 | the interned string -- which is \var{string} itself or a copy. |
| 234 | Interning strings is useful to gain a little performance on |
| 235 | dictionary lookup -- if the keys in a dictionary are interned, and |
| 236 | the lookup key is interned, the key comparisons (after hashing) can |
| 237 | be done by a pointer compare instead of a string compare. Normally, |
| 238 | the names used in Python programs are automatically interned, and |
| 239 | the dictionaries used to hold module, class or instance attributes |
| 240 | have interned keys. Interned strings are immortal (i.e. never get |
| 241 | garbage collected). |
| 242 | \end{funcdesc} |
| 243 | |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 244 | \begin{funcdesc}{int}{x} |
Guido van Rossum | 1cd26f2 | 1997-04-02 06:04:02 +0000 | [diff] [blame] | 245 | Convert a string or number to a plain integer. If the argument is a |
| 246 | string, it must contain a possibly singed decimal number |
| 247 | representable as a Python integer, possibly embedded in whitespace; |
| 248 | this behaves identical to \code{string.atoi(\var{x})}. |
| 249 | Otherwise, the argument may be a plain or |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 250 | long integer or a floating point number. Conversion of floating |
| 251 | point numbers to integers is defined by the C semantics; normally |
Guido van Rossum | ecde781 | 1995-03-28 13:35:14 +0000 | [diff] [blame] | 252 | the conversion truncates towards zero.\footnote{This is ugly --- the |
| 253 | language definition should require truncation towards zero.} |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 254 | \end{funcdesc} |
| 255 | |
| 256 | \begin{funcdesc}{len}{s} |
| 257 | Return the length (the number of items) of an object. The argument |
| 258 | may be a sequence (string, tuple or list) or a mapping (dictionary). |
| 259 | \end{funcdesc} |
| 260 | |
Guido van Rossum | 921f32c | 1997-06-02 17:21:20 +0000 | [diff] [blame^] | 261 | \begin{funcdesc}{list}{sequence} |
| 262 | Return a list whose items are the same and in the same order as |
| 263 | \var{sequence}'s items. If \var{sequence} is already a list, |
| 264 | a copy is made and returned, similar to \code{\var{sequence}[:]}. |
| 265 | For instance, \code{list('abc')} returns |
| 266 | returns \code{['a', 'b', 'c']} and \code{list( (1, 2, 3) )} returns |
| 267 | \code{[1, 2, 3]}. |
| 268 | \end{funcdesc} |
| 269 | |
Guido van Rossum | fb502e9 | 1995-07-07 22:58:28 +0000 | [diff] [blame] | 270 | \begin{funcdesc}{locals}{} |
| 271 | Return a dictionary representing the current local symbol table. |
| 272 | Inside a function, modifying this dictionary does not always have the |
| 273 | desired effect. |
| 274 | \end{funcdesc} |
| 275 | |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 276 | \begin{funcdesc}{long}{x} |
Guido van Rossum | 1cd26f2 | 1997-04-02 06:04:02 +0000 | [diff] [blame] | 277 | Convert a string or number to a long integer. If the argument is a |
| 278 | string, it must contain a possibly singed decimal number of |
| 279 | arbitrary size, possibly embedded in whitespace; |
| 280 | this behaves identical to \code{string.atol(\var{x})}. |
| 281 | Otherwise, the argument may be a plain or |
| 282 | long integer or a floating point number, and a long interger with |
| 283 | the same value is returned. Conversion of floating |
| 284 | point numbers to integers is defined by the C semantics; |
| 285 | see the description of \code{int()}. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 286 | \end{funcdesc} |
| 287 | |
| 288 | \begin{funcdesc}{map}{function\, list\, ...} |
| 289 | Apply \var{function} to every item of \var{list} and return a list |
| 290 | of the results. If additional \var{list} arguments are passed, |
| 291 | \var{function} must take that many arguments and is applied to |
| 292 | the items of all lists in parallel; if a list is shorter than another |
| 293 | it is assumed to be extended with \code{None} items. If |
| 294 | \var{function} is \code{None}, the identity function is assumed; if |
| 295 | there are multiple list arguments, \code{map} returns a list |
| 296 | consisting of tuples containing the corresponding items from all lists |
| 297 | (i.e. a kind of transpose operation). The \var{list} arguments may be |
| 298 | any kind of sequence; the result is always a list. |
| 299 | \end{funcdesc} |
| 300 | |
| 301 | \begin{funcdesc}{max}{s} |
| 302 | Return the largest item of a non-empty sequence (string, tuple or |
| 303 | list). |
| 304 | \end{funcdesc} |
| 305 | |
| 306 | \begin{funcdesc}{min}{s} |
| 307 | Return the smallest item of a non-empty sequence (string, tuple or |
| 308 | list). |
| 309 | \end{funcdesc} |
| 310 | |
| 311 | \begin{funcdesc}{oct}{x} |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 312 | Convert an integer number (of any size) to an octal string. The |
Guido van Rossum | 5cd7520 | 1997-01-14 18:44:23 +0000 | [diff] [blame] | 313 | result is a valid Python expression. Note: this always yields |
| 314 | an unsigned literal, e.g. on a 32-bit machine, \code{oct(-1)} yields |
| 315 | \code{'037777777777'}. When evaluated on a machine with the same |
| 316 | word size, this literal is evaluated as -1; at a different word |
| 317 | size, it may turn up as a large positive number or raise an |
| 318 | \code{OverflowError} exception. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 319 | \end{funcdesc} |
| 320 | |
Guido van Rossum | 7f49b7a | 1995-01-12 12:38:46 +0000 | [diff] [blame] | 321 | \begin{funcdesc}{open}{filename\optional{\, mode\optional{\, bufsize}}} |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 322 | Return a new file object (described earlier under Built-in Types). |
Guido van Rossum | 041be05 | 1994-05-03 14:46:50 +0000 | [diff] [blame] | 323 | The first two arguments are the same as for \code{stdio}'s |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 324 | \code{fopen()}: \var{filename} is the file name to be opened, |
| 325 | \var{mode} indicates how the file is to be opened: \code{'r'} for |
| 326 | reading, \code{'w'} for writing (truncating an existing file), and |
Guido van Rossum | 1dde7b7 | 1996-10-11 15:57:17 +0000 | [diff] [blame] | 327 | \code{'a'} opens it for appending (which on {\em some} \UNIX{} |
Guido van Rossum | 59b328e | 1996-05-02 15:16:59 +0000 | [diff] [blame] | 328 | systems means that {\em all} writes append to the end of the file, |
| 329 | regardless of the current seek position). |
| 330 | Modes \code{'r+'}, \code{'w+'} and |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 331 | \code{'a+'} open the file for updating, provided the underlying |
| 332 | \code{stdio} library understands this. On systems that differentiate |
| 333 | between binary and text files, \code{'b'} appended to the mode opens |
| 334 | the file in binary mode. If the file cannot be opened, \code{IOError} |
| 335 | is raised. |
Guido van Rossum | 041be05 | 1994-05-03 14:46:50 +0000 | [diff] [blame] | 336 | If \var{mode} is omitted, it defaults to \code{'r'}. |
| 337 | The optional \var{bufsize} argument specifies the file's desired |
| 338 | buffer size: 0 means unbuffered, 1 means line buffered, any other |
| 339 | positive value means use a buffer of (approximately) that size. A |
| 340 | negative \var{bufsize} means to use the system default, which is |
| 341 | usually line buffered for for tty devices and fully buffered for other |
| 342 | files.% |
| 343 | \footnote{Specifying a buffer size currently has no effect on systems |
| 344 | that don't have \code{setvbuf()}. The interface to specify the buffer |
| 345 | size is not done using a method that calls \code{setvbuf()}, because |
| 346 | that may dump core when called after any I/O has been performed, and |
| 347 | there's no reliable way to determine whether this is the case.} |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 348 | \end{funcdesc} |
| 349 | |
| 350 | \begin{funcdesc}{ord}{c} |
| 351 | Return the \ASCII{} value of a string of one character. E.g., |
| 352 | \code{ord('a')} returns the integer \code{97}. This is the inverse of |
| 353 | \code{chr()}. |
| 354 | \end{funcdesc} |
| 355 | |
Guido van Rossum | 16d6e71 | 1994-08-08 12:30:22 +0000 | [diff] [blame] | 356 | \begin{funcdesc}{pow}{x\, y\optional{\, z}} |
Guido van Rossum | b8b264b | 1994-08-12 13:13:50 +0000 | [diff] [blame] | 357 | Return \var{x} to the power \var{y}; if \var{z} is present, return |
| 358 | \var{x} to the power \var{y}, modulo \var{z} (computed more |
Guido van Rossum | 6c4f003 | 1995-03-07 10:14:09 +0000 | [diff] [blame] | 359 | efficiently than \code{pow(\var{x}, \var{y}) \% \var{z}}). |
Guido van Rossum | b8b264b | 1994-08-12 13:13:50 +0000 | [diff] [blame] | 360 | The arguments must have |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 361 | numeric types. With mixed operand types, the rules for binary |
| 362 | arithmetic operators apply. The effective operand type is also the |
| 363 | type of the result; if the result is not expressible in this type, the |
Guido van Rossum | 16d6e71 | 1994-08-08 12:30:22 +0000 | [diff] [blame] | 364 | function raises an exception; e.g., \code{pow(2, -1)} or \code{pow(2, |
| 365 | 35000)} is not allowed. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 366 | \end{funcdesc} |
| 367 | |
Guido van Rossum | 16d6e71 | 1994-08-08 12:30:22 +0000 | [diff] [blame] | 368 | \begin{funcdesc}{range}{\optional{start\,} end\optional{\, step}} |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 369 | This is a versatile function to create lists containing arithmetic |
| 370 | progressions. It is most often used in \code{for} loops. The |
| 371 | arguments must be plain integers. If the \var{step} argument is |
| 372 | omitted, it defaults to \code{1}. If the \var{start} argument is |
| 373 | omitted, it defaults to \code{0}. The full form returns a list of |
| 374 | plain integers \code{[\var{start}, \var{start} + \var{step}, |
| 375 | \var{start} + 2 * \var{step}, \ldots]}. If \var{step} is positive, |
| 376 | the last element is the largest \code{\var{start} + \var{i} * |
| 377 | \var{step}} less than \var{end}; if \var{step} is negative, the last |
| 378 | element is the largest \code{\var{start} + \var{i} * \var{step}} |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 379 | greater than \var{end}. \var{step} must not be zero (or else an |
| 380 | exception is raised). Example: |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 381 | |
| 382 | \bcode\begin{verbatim} |
| 383 | >>> range(10) |
| 384 | [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] |
| 385 | >>> range(1, 11) |
| 386 | [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] |
| 387 | >>> range(0, 30, 5) |
| 388 | [0, 5, 10, 15, 20, 25] |
| 389 | >>> range(0, 10, 3) |
| 390 | [0, 3, 6, 9] |
| 391 | >>> range(0, -10, -1) |
| 392 | [0, -1, -2, -3, -4, -5, -6, -7, -8, -9] |
| 393 | >>> range(0) |
| 394 | [] |
| 395 | >>> range(1, 0) |
| 396 | [] |
| 397 | >>> |
| 398 | \end{verbatim}\ecode |
| 399 | \end{funcdesc} |
| 400 | |
Guido van Rossum | 16d6e71 | 1994-08-08 12:30:22 +0000 | [diff] [blame] | 401 | \begin{funcdesc}{raw_input}{\optional{prompt}} |
| 402 | If the \var{prompt} argument is present, it is written to standard output |
| 403 | without a trailing newline. The function then reads a line from input, |
| 404 | converts it to a string (stripping a trailing newline), and returns that. |
| 405 | When \EOF{} is read, \code{EOFError} is raised. Example: |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 406 | |
| 407 | \bcode\begin{verbatim} |
| 408 | >>> s = raw_input('--> ') |
| 409 | --> Monty Python's Flying Circus |
| 410 | >>> s |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 411 | "Monty Python's Flying Circus" |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 412 | >>> |
| 413 | \end{verbatim}\ecode |
Guido van Rossum | 921f32c | 1997-06-02 17:21:20 +0000 | [diff] [blame^] | 414 | |
| 415 | If the interpreter was built to use the GNU readline library, then |
| 416 | \code{raw_input()} will use it to provide elaborate |
| 417 | line editing and history features. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 418 | \end{funcdesc} |
| 419 | |
Guido van Rossum | 16d6e71 | 1994-08-08 12:30:22 +0000 | [diff] [blame] | 420 | \begin{funcdesc}{reduce}{function\, list\optional{\, initializer}} |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 421 | Apply the binary \var{function} to the items of \var{list} so as to |
| 422 | reduce the list to a single value. E.g., |
| 423 | \code{reduce(lambda x, y: x*y, \var{list}, 1)} returns the product of |
| 424 | the elements of \var{list}. The optional \var{initializer} can be |
| 425 | thought of as being prepended to \var{list} so as to allow reduction |
| 426 | of an empty \var{list}. The \var{list} arguments may be any kind of |
| 427 | sequence. |
| 428 | \end{funcdesc} |
| 429 | |
| 430 | \begin{funcdesc}{reload}{module} |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 431 | Re-parse and re-initialize an already imported \var{module}. The |
| 432 | argument must be a module object, so it must have been successfully |
| 433 | imported before. This is useful if you have edited the module source |
| 434 | file using an external editor and want to try out the new version |
| 435 | without leaving the Python interpreter. The return value is the |
| 436 | module object (i.e.\ the same as the \var{module} argument). |
| 437 | |
| 438 | There are a number of caveats: |
| 439 | |
| 440 | If a module is syntactically correct but its initialization fails, the |
| 441 | first \code{import} statement for it does not bind its name locally, |
| 442 | but does store a (partially initialized) module object in |
| 443 | \code{sys.modules}. To reload the module you must first |
| 444 | \code{import} it again (this will bind the name to the partially |
| 445 | initialized module object) before you can \code{reload()} it. |
| 446 | |
| 447 | When a module is reloaded, its dictionary (containing the module's |
| 448 | global variables) is retained. Redefinitions of names will override |
| 449 | the old definitions, so this is generally not a problem. If the new |
| 450 | version of a module does not define a name that was defined by the old |
| 451 | version, the old definition remains. This feature can be used to the |
| 452 | module's advantage if it maintains a global table or cache of objects |
| 453 | --- with a \code{try} statement it can test for the table's presence |
| 454 | and skip its initialization if desired. |
| 455 | |
| 456 | It is legal though generally not very useful to reload built-in or |
| 457 | dynamically loaded modules, except for \code{sys}, \code{__main__} and |
| 458 | \code{__builtin__}. In certain cases, however, extension modules are |
| 459 | not designed to be initialized more than once, and may fail in |
| 460 | arbitrary ways when reloaded. |
| 461 | |
| 462 | If a module imports objects from another module using \code{from} |
Fred Drake | 4b3f031 | 1996-12-13 22:04:31 +0000 | [diff] [blame] | 463 | \ldots{} \code{import} \ldots{}, calling \code{reload()} for the other |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 464 | module does not redefine the objects imported from it --- one way |
| 465 | around this is to re-execute the \code{from} statement, another is to |
| 466 | use \code{import} and qualified names (\var{module}.\var{name}) |
| 467 | instead. |
| 468 | |
| 469 | If a module instantiates instances of a class, reloading the module |
| 470 | that defines the class does not affect the method definitions of the |
| 471 | instances --- they continue to use the old class definition. The same |
| 472 | is true for derived classes. |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 473 | \end{funcdesc} |
| 474 | |
| 475 | \begin{funcdesc}{repr}{object} |
| 476 | Return a string containing a printable representation of an object. |
| 477 | This is the same value yielded by conversions (reverse quotes). |
| 478 | It is sometimes useful to be able to access this operation as an |
| 479 | ordinary function. For many types, this function makes an attempt |
| 480 | to return a string that would yield an object with the same value |
| 481 | when passed to \code{eval()}. |
| 482 | \end{funcdesc} |
| 483 | |
| 484 | \begin{funcdesc}{round}{x\, n} |
| 485 | Return the floating point value \var{x} rounded to \var{n} digits |
| 486 | after the decimal point. If \var{n} is omitted, it defaults to zero. |
| 487 | The result is a floating point number. Values are rounded to the |
| 488 | closest multiple of 10 to the power minus \var{n}; if two multiples |
| 489 | are equally close, rounding is done away from 0 (so e.g. |
| 490 | \code{round(0.5)} is \code{1.0} and \code{round(-0.5)} is \code{-1.0}). |
| 491 | \end{funcdesc} |
| 492 | |
| 493 | \begin{funcdesc}{setattr}{object\, name\, value} |
| 494 | This is the counterpart of \code{getattr}. The arguments are an |
| 495 | object, a string and an arbitrary value. The string must be the name |
| 496 | of one of the object's attributes. The function assigns the value to |
| 497 | the attribute, provided the object allows it. For example, |
| 498 | \code{setattr(\var{x}, '\var{foobar}', 123)} is equivalent to |
| 499 | \code{\var{x}.\var{foobar} = 123}. |
| 500 | \end{funcdesc} |
| 501 | |
| 502 | \begin{funcdesc}{str}{object} |
| 503 | Return a string containing a nicely printable representation of an |
| 504 | object. For strings, this returns the string itself. The difference |
Guido van Rossum | 6c4f003 | 1995-03-07 10:14:09 +0000 | [diff] [blame] | 505 | with \code{repr(\var{object})} is that \code{str(\var{object})} does not |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 506 | always attempt to return a string that is acceptable to \code{eval()}; |
| 507 | its goal is to return a printable string. |
| 508 | \end{funcdesc} |
| 509 | |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 510 | \begin{funcdesc}{tuple}{sequence} |
Guido van Rossum | b8b264b | 1994-08-12 13:13:50 +0000 | [diff] [blame] | 511 | Return a tuple whose items are the same and in the same order as |
Guido van Rossum | 921f32c | 1997-06-02 17:21:20 +0000 | [diff] [blame^] | 512 | \var{sequence}'s items. If \var{sequence} is already a tuple, it |
Guido van Rossum | b8b264b | 1994-08-12 13:13:50 +0000 | [diff] [blame] | 513 | is returned unchanged. For instance, \code{tuple('abc')} returns |
| 514 | returns \code{('a', 'b', 'c')} and \code{tuple([1, 2, 3])} returns |
| 515 | \code{(1, 2, 3)}. |
| 516 | \end{funcdesc} |
| 517 | |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 518 | \begin{funcdesc}{type}{object} |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 519 | Return the type of an \var{object}. The return value is a type |
| 520 | object. The standard module \code{types} defines names for all |
| 521 | built-in types. |
| 522 | \stmodindex{types} |
| 523 | \obindex{type} |
| 524 | For instance: |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 525 | |
| 526 | \bcode\begin{verbatim} |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 527 | >>> import types |
| 528 | >>> if type(x) == types.StringType: print "It's a string" |
Guido van Rossum | 5fdeeea | 1994-01-02 01:22:07 +0000 | [diff] [blame] | 529 | \end{verbatim}\ecode |
| 530 | \end{funcdesc} |
Guido van Rossum | 68cfbe7 | 1994-02-24 11:28:27 +0000 | [diff] [blame] | 531 | |
Guido van Rossum | 6bb1adc | 1995-03-13 10:03:32 +0000 | [diff] [blame] | 532 | \begin{funcdesc}{vars}{\optional{object}} |
Guido van Rossum | 1738311 | 1994-04-21 10:32:28 +0000 | [diff] [blame] | 533 | Without arguments, return a dictionary corresponding to the current |
| 534 | local symbol table. With a module, class or class instance object as |
| 535 | argument (or anything else that has a \code{__dict__} attribute), |
| 536 | returns a dictionary corresponding to the object's symbol table. |
| 537 | The returned dictionary should not be modified: the effects on the |
| 538 | corresponding symbol table are undefined.% |
| 539 | \footnote{In the current implementation, local variable bindings |
| 540 | cannot normally be affected this way, but variables retrieved from |
Guido van Rossum | 6c4f003 | 1995-03-07 10:14:09 +0000 | [diff] [blame] | 541 | other scopes (e.g. modules) can be. This may change.} |
Guido van Rossum | 1738311 | 1994-04-21 10:32:28 +0000 | [diff] [blame] | 542 | \end{funcdesc} |
| 543 | |
Guido van Rossum | 16d6e71 | 1994-08-08 12:30:22 +0000 | [diff] [blame] | 544 | \begin{funcdesc}{xrange}{\optional{start\,} end\optional{\, step}} |
Guido van Rossum | 68cfbe7 | 1994-02-24 11:28:27 +0000 | [diff] [blame] | 545 | This function is very similar to \code{range()}, but returns an |
| 546 | ``xrange object'' instead of a list. This is an opaque sequence type |
| 547 | which yields the same values as the corresponding list, without |
| 548 | actually storing them all simultaneously. The advantage of |
| 549 | \code{xrange()} over \code{range()} is minimal (since \code{xrange()} |
| 550 | still has to create the values when asked for them) except when a very |
Guido van Rossum | 470be14 | 1995-03-17 16:07:09 +0000 | [diff] [blame] | 551 | large range is used on a memory-starved machine (e.g. MS-DOS) or when all |
Guido van Rossum | 68cfbe7 | 1994-02-24 11:28:27 +0000 | [diff] [blame] | 552 | of the range's elements are never used (e.g. when the loop is usually |
| 553 | terminated with \code{break}). |
| 554 | \end{funcdesc} |