Merged revisions 61724-61725,61731-61735,61737,61739,61741,61743-61744,61753,61761,61765-61767,61769,61773,61776-61778,61780-61783,61788,61793,61796,61807,61813 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
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r61724 | martin.v.loewis | 2008-03-22 01:01:12 +0100 (Sat, 22 Mar 2008) | 49 lines
Merged revisions 61602-61723 via svnmerge from
svn+ssh://pythondev@svn.python.org/sandbox/trunk/2to3/lib2to3
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r61626 | david.wolever | 2008-03-19 17:19:16 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line
Added fixer for implicit local imports. See #2414.
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r61628 | david.wolever | 2008-03-19 17:57:43 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line
Added a class for tests which should not run if a particular import is found.
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r61629 | collin.winter | 2008-03-19 17:58:19 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line
Two more relative import fixes in pgen2.
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r61635 | david.wolever | 2008-03-19 20:16:03 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line
Fixed print fixer so it will do the Right Thing when it encounters __future__.print_function. 2to3 gets upset, though, so the tests have been commented out.
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r61637 | david.wolever | 2008-03-19 21:37:17 +0100 (Mi, 19 M?\195?\164r 2008) | 3 lines
Added a fixer for itertools imports (from itertools import imap, ifilterfalse --> from itertools import filterfalse)
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r61645 | david.wolever | 2008-03-19 23:22:35 +0100 (Mi, 19 M?\195?\164r 2008) | 1 line
SVN is happier when you add the files you create... -_-'
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r61654 | david.wolever | 2008-03-20 01:09:56 +0100 (Do, 20 M?\195?\164r 2008) | 1 line
Added an explicit sort order to fixers -- fixes problems like #2427
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r61664 | david.wolever | 2008-03-20 04:32:40 +0100 (Do, 20 M?\195?\164r 2008) | 3 lines
Fixes #2428 -- comments are no longer eatten by __future__ fixer.
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r61673 | david.wolever | 2008-03-20 17:22:40 +0100 (Do, 20 M?\195?\164r 2008) | 1 line
Added 2to3 node pretty-printer
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r61679 | david.wolever | 2008-03-20 20:50:42 +0100 (Do, 20 M?\195?\164r 2008) | 1 line
Made node printing a little bit prettier
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r61723 | martin.v.loewis | 2008-03-22 00:59:27 +0100 (Sa, 22 M?\195?\164r 2008) | 2 lines
Fix whitespace.
........
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r61725 | martin.v.loewis | 2008-03-22 01:02:41 +0100 (Sat, 22 Mar 2008) | 2 lines
Install lib2to3.
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r61731 | facundo.batista | 2008-03-22 03:45:37 +0100 (Sat, 22 Mar 2008) | 4 lines
Small fix that complicated the test actually when that
test failed.
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r61732 | alexandre.vassalotti | 2008-03-22 05:08:44 +0100 (Sat, 22 Mar 2008) | 2 lines
Added warning for the removal of 'hotshot' in Py3k.
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r61733 | georg.brandl | 2008-03-22 11:07:29 +0100 (Sat, 22 Mar 2008) | 4 lines
#1918: document that weak references *to* an object are
cleared before the object's __del__ is called, to ensure that the weak
reference callback (if any) finds the object healthy.
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r61734 | georg.brandl | 2008-03-22 11:56:23 +0100 (Sat, 22 Mar 2008) | 2 lines
Activate the Sphinx doctest extension and convert howto/functional to use it.
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r61735 | georg.brandl | 2008-03-22 11:58:38 +0100 (Sat, 22 Mar 2008) | 2 lines
Allow giving source names on the cmdline.
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r61737 | georg.brandl | 2008-03-22 12:00:48 +0100 (Sat, 22 Mar 2008) | 2 lines
Fixup this HOWTO's doctest blocks so that they can be run with sphinx' doctest builder.
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r61739 | georg.brandl | 2008-03-22 12:47:10 +0100 (Sat, 22 Mar 2008) | 2 lines
Test decimal.rst doctests as far as possible with sphinx doctest.
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r61741 | georg.brandl | 2008-03-22 13:04:26 +0100 (Sat, 22 Mar 2008) | 2 lines
Make doctests in re docs usable with sphinx' doctest.
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r61743 | georg.brandl | 2008-03-22 13:59:37 +0100 (Sat, 22 Mar 2008) | 2 lines
Make more doctests in pprint docs testable.
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r61744 | georg.brandl | 2008-03-22 14:07:06 +0100 (Sat, 22 Mar 2008) | 2 lines
No need to specify explicit "doctest_block" anymore.
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r61753 | georg.brandl | 2008-03-22 21:08:43 +0100 (Sat, 22 Mar 2008) | 2 lines
Fix-up syntax problems.
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r61761 | georg.brandl | 2008-03-22 22:06:20 +0100 (Sat, 22 Mar 2008) | 4 lines
Make collections' doctests executable.
(The <BLANKLINE>s will be stripped from presentation output.)
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r61765 | georg.brandl | 2008-03-22 22:21:57 +0100 (Sat, 22 Mar 2008) | 2 lines
Test doctests in datetime docs.
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r61766 | georg.brandl | 2008-03-22 22:26:44 +0100 (Sat, 22 Mar 2008) | 2 lines
Test doctests in operator docs.
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r61767 | georg.brandl | 2008-03-22 22:38:33 +0100 (Sat, 22 Mar 2008) | 2 lines
Enable doctests in functions.rst. Already found two errors :)
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r61769 | georg.brandl | 2008-03-22 23:04:10 +0100 (Sat, 22 Mar 2008) | 3 lines
Enable doctest running for several other documents.
We have now over 640 doctests that are run with "make doctest".
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r61773 | raymond.hettinger | 2008-03-23 01:55:46 +0100 (Sun, 23 Mar 2008) | 1 line
Simplify demo code.
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r61776 | neal.norwitz | 2008-03-23 04:43:33 +0100 (Sun, 23 Mar 2008) | 7 lines
Try to make this test a little more robust and not fail with:
timeout (10.0025) is more than 2 seconds more than expected (0.001)
I'm assuming this problem is caused by DNS lookup. This change
does a DNS lookup of the hostname before trying to connect, so the time
is not included.
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r61777 | neal.norwitz | 2008-03-23 05:08:30 +0100 (Sun, 23 Mar 2008) | 1 line
Speed up the test by avoiding socket timeouts.
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r61778 | neal.norwitz | 2008-03-23 05:43:09 +0100 (Sun, 23 Mar 2008) | 1 line
Skip the epoll test if epoll() does not work
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r61780 | neal.norwitz | 2008-03-23 06:47:20 +0100 (Sun, 23 Mar 2008) | 1 line
Suppress failure (to avoid a flaky test) if we cannot connect to svn.python.org
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r61781 | neal.norwitz | 2008-03-23 07:13:25 +0100 (Sun, 23 Mar 2008) | 4 lines
Move itertools before future_builtins since the latter depends on the former.
From a clean build importing future_builtins would fail since itertools
wasn't built yet.
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r61782 | neal.norwitz | 2008-03-23 07:16:04 +0100 (Sun, 23 Mar 2008) | 1 line
Try to prevent the alarm going off early in tearDown
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r61783 | neal.norwitz | 2008-03-23 07:19:57 +0100 (Sun, 23 Mar 2008) | 4 lines
Remove compiler warnings (on Alpha at least) about using chars as
array subscripts. Using chars are dangerous b/c they are signed
on some platforms and unsigned on others.
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r61788 | georg.brandl | 2008-03-23 09:05:30 +0100 (Sun, 23 Mar 2008) | 2 lines
Make the doctests presentation-friendlier.
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r61793 | amaury.forgeotdarc | 2008-03-23 10:55:29 +0100 (Sun, 23 Mar 2008) | 4 lines
#1477: ur'\U0010FFFF' raised in narrow unicode builds.
Corrected the raw-unicode-escape codec to use UTF-16 surrogates in
this case, just like the unicode-escape codec.
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r61796 | raymond.hettinger | 2008-03-23 14:32:32 +0100 (Sun, 23 Mar 2008) | 1 line
Issue 1681432: Add triangular distribution the random module.
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r61807 | raymond.hettinger | 2008-03-23 20:37:53 +0100 (Sun, 23 Mar 2008) | 4 lines
Adopt Nick's suggestion for useful default arguments.
Clean-up floating point issues by adding true division and float constants.
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r61813 | gregory.p.smith | 2008-03-23 22:04:43 +0100 (Sun, 23 Mar 2008) | 6 lines
Fix gzip to deal with CRC's being signed values in Python 2.x properly and to
read 32bit values as unsigned to start with rather than applying signedness
fixups allover the place afterwards.
This hopefully fixes the test_tarfile failure on the alpha/tru64 buildbot.
................
diff --git a/Doc/howto/functional.rst b/Doc/howto/functional.rst
index e7b23b7..a81e5eb 100644
--- a/Doc/howto/functional.rst
+++ b/Doc/howto/functional.rst
@@ -2,7 +2,7 @@
Functional Programming HOWTO
********************************
-:Author: \A. M. Kuchling
+:Author: A. M. Kuchling
:Release: 0.31
(This is a first draft. Please send comments/error reports/suggestions to
@@ -98,6 +98,7 @@
* Composability.
* Ease of debugging and testing.
+
Formal provability
------------------
@@ -133,6 +134,7 @@
proof; maybe there's an error in it, and you wrongly believe you've proved the
program correct.
+
Modularity
----------
@@ -159,7 +161,6 @@
check that the output matches expectations.
-
Composability
-------------
@@ -175,7 +176,6 @@
a few functions specialized for the current task.
-
Iterators
=========
@@ -197,12 +197,12 @@
dictionaries. An object is called an **iterable** object if you can get an
iterator for it.
-You can experiment with the iteration interface manually::
+You can experiment with the iteration interface manually:
>>> L = [1,2,3]
>>> it = iter(L)
>>> it
- <iterator object at 0x8116870>
+ <...iterator object at ...>
>>> it.next()
1
>>> it.next()
@@ -220,14 +220,15 @@
be an iterator or some object for which ``iter()`` can create an iterator.
These two statements are equivalent::
- for i in iter(obj):
- print(i)
- for i in obj:
- print(i)
+ for i in iter(obj):
+ print i
+
+ for i in obj:
+ print i
Iterators can be materialized as lists or tuples by using the :func:`list` or
-:func:`tuple` constructor functions::
+:func:`tuple` constructor functions:
>>> L = [1,2,3]
>>> iterator = iter(L)
@@ -236,7 +237,7 @@
(1, 2, 3)
Sequence unpacking also supports iterators: if you know an iterator will return
-N elements, you can unpack them into an N-tuple::
+N elements, you can unpack them into an N-tuple:
>>> L = [1,2,3]
>>> iterator = iter(L)
@@ -269,7 +270,11 @@
iterator.
Calling :func:`iter` on a dictionary returns an iterator that will loop over the
-dictionary's keys::
+dictionary's keys:
+
+.. not a doctest since dict ordering varies across Pythons
+
+::
>>> m = {'Jan': 1, 'Feb': 2, 'Mar': 3, 'Apr': 4, 'May': 5, 'Jun': 6,
... 'Jul': 7, 'Aug': 8, 'Sep': 9, 'Oct': 10, 'Nov': 11, 'Dec': 12}
@@ -279,11 +284,11 @@
Feb 2
Aug 8
Sep 9
- May 5
+ Apr 4
Jun 6
Jul 7
Jan 1
- Apr 4
+ May 5
Nov 11
Dec 12
Oct 10
@@ -297,7 +302,7 @@
:meth:`values` or :meth:`items` methods to get an appropriate iterator.
The :func:`dict` constructor can accept an iterator that returns a finite stream
-of ``(key, value)`` tuples::
+of ``(key, value)`` tuples:
>>> L = [('Italy', 'Rome'), ('France', 'Paris'), ('US', 'Washington DC')]
>>> dict(iter(L))
@@ -334,18 +339,18 @@
functional programming language Haskell (http://www.haskell.org). You can strip
all the whitespace from a stream of strings with the following code::
- line_list = [' line 1\n', 'line 2 \n', ...]
+ line_list = [' line 1\n', 'line 2 \n', ...]
- # Generator expression -- returns iterator
- stripped_iter = (line.strip() for line in line_list)
+ # Generator expression -- returns iterator
+ stripped_iter = (line.strip() for line in line_list)
- # List comprehension -- returns list
- stripped_list = [line.strip() for line in line_list]
+ # List comprehension -- returns list
+ stripped_list = [line.strip() for line in line_list]
You can select only certain elements by adding an ``"if"`` condition::
- stripped_list = [line.strip() for line in line_list
- if line != ""]
+ stripped_list = [line.strip() for line in line_list
+ if line != ""]
With a list comprehension, you get back a Python list; ``stripped_list`` is a
list containing the resulting lines, not an iterator. Generator expressions
@@ -378,7 +383,7 @@
parentheses signalling a function call also count. If you want to create an
iterator that will be immediately passed to a function you can write::
- obj_total = sum(obj.count for obj in list_all_objects())
+ obj_total = sum(obj.count for obj in list_all_objects())
The ``for...in`` clauses contain the sequences to be iterated over. The
sequences do not have to be the same length, because they are iterated over from
@@ -406,11 +411,14 @@
This means that when there are multiple ``for...in`` clauses but no ``if``
clauses, the length of the resulting output will be equal to the product of the
lengths of all the sequences. If you have two lists of length 3, the output
-list is 9 elements long::
+list is 9 elements long:
- seq1 = 'abc'
- seq2 = (1,2,3)
- >>> [ (x,y) for x in seq1 for y in seq2]
+.. doctest::
+ :options: +NORMALIZE_WHITESPACE
+
+ >>> seq1 = 'abc'
+ >>> seq2 = (1,2,3)
+ >>> [(x,y) for x in seq1 for y in seq2]
[('a', 1), ('a', 2), ('a', 3),
('b', 1), ('b', 2), ('b', 3),
('c', 1), ('c', 2), ('c', 3)]
@@ -441,7 +449,9 @@
function? What if you could later resume the function where it left off? This
is what generators provide; they can be thought of as resumable functions.
-Here's the simplest example of a generator function::
+Here's the simplest example of a generator function:
+
+.. testcode::
def generate_ints(N):
for i in range(N):
@@ -459,11 +469,11 @@
suspended and local variables are preserved. On the next call to the
generator's ``.next()`` method, the function will resume executing.
-Here's a sample usage of the ``generate_ints()`` generator::
+Here's a sample usage of the ``generate_ints()`` generator:
>>> gen = generate_ints(3)
>>> gen
- <generator object at 0x8117f90>
+ <generator object at ...>
>>> gen.next()
0
>>> gen.next()
@@ -496,9 +506,7 @@
The test suite included with Python's library, ``test_generators.py``, contains
a number of more interesting examples. Here's one generator that implements an
-in-order traversal of a tree using generators recursively.
-
-::
+in-order traversal of a tree using generators recursively. ::
# A recursive generator that generates Tree leaves in in-order.
def inorder(t):
@@ -553,7 +561,7 @@
Here's a simple counter that increments by 1 and allows changing the value of
the internal counter.
-::
+.. testcode::
def counter (maximum):
i = 0
@@ -622,15 +630,14 @@
``map(f, iterA, iterB, ...)`` returns an iterator over the sequence
``f(iterA[0], iterB[0]), f(iterA[1], iterB[1]), f(iterA[2], iterB[2]), ...``.
-::
+ >>> def upper(s):
+ ... return s.upper()
- def upper(s):
- return s.upper()
- list(map(upper, ['sentence', 'fragment'])) =>
- ['SENTENCE', 'FRAGMENT']
- list(upper(s) for s in ['sentence', 'fragment']) =>
- ['SENTENCE', 'FRAGMENT']
+ >>> map(upper, ['sentence', 'fragment'])
+ ['SENTENCE', 'FRAGMENT']
+ >>> [upper(s) for s in ['sentence', 'fragment']]
+ ['SENTENCE', 'FRAGMENT']
You can of course achieve the same effect with a list comprehension.
@@ -640,15 +647,14 @@
some condition; for use with :func:`filter`, the predicate must take a single
value.
-::
+ >>> def is_even(x):
+ ... return (x % 2) == 0
- def is_even(x):
- return (x % 2) == 0
+ >>> filter(is_even, range(10))
+ [0, 2, 4, 6, 8]
- list(filter(is_even, range(10))) =>
- [0, 2, 4, 6, 8]
-This can also be written as a generator expression::
+This can also be written as a list comprehension:
>>> list(x for x in range(10) if is_even(x))
[0, 2, 4, 6, 8]
@@ -664,27 +670,41 @@
raised. If the initial value is supplied, it's used as a starting point and
``func(initial_value, A)`` is the first calculation. ::
- import operator
- import functools
- functools.reduce(operator.concat, ['A', 'BB', 'C']) =>
- 'ABBC'
- functools.reduce(operator.concat, []) =>
- TypeError: reduce() of empty sequence with no initial value
- functools.reduce(operator.mul, [1,2,3], 1) =>
- 6
- functools.reduce(operator.mul, [], 1) =>
- 1
-
-If you use :func:`operator.add` with :func:`functools.reduce`, you'll add up all
-the elements of the iterable. This case is so common that there's a special
-built-in called :func:`sum` to compute it::
- functools.reduce(operator.add, [1,2,3,4], 0) =>
- 10
- sum([1,2,3,4]) =>
- 10
- sum([]) =>
- 0
+``reduce(func, iter, [initial_value])`` doesn't have a counterpart in the
+:mod:`itertools` module because it cumulatively performs an operation on all the
+iterable's elements and therefore can't be applied to infinite iterables.
+``func`` must be a function that takes two elements and returns a single value.
+:func:`reduce` takes the first two elements A and B returned by the iterator and
+calculates ``func(A, B)``. It then requests the third element, C, calculates
+``func(func(A, B), C)``, combines this result with the fourth element returned,
+and continues until the iterable is exhausted. If the iterable returns no
+values at all, a :exc:`TypeError` exception is raised. If the initial value is
+supplied, it's used as a starting point and ``func(initial_value, A)`` is the
+first calculation.
+
+ >>> import operator
+ >>> reduce(operator.concat, ['A', 'BB', 'C'])
+ 'ABBC'
+ >>> reduce(operator.concat, [])
+ Traceback (most recent call last):
+ ...
+ TypeError: reduce() of empty sequence with no initial value
+ >>> reduce(operator.mul, [1,2,3], 1)
+ 6
+ >>> reduce(operator.mul, [], 1)
+ 1
+
+If you use :func:`operator.add` with :func:`reduce`, you'll add up all the
+elements of the iterable. This case is so common that there's a special
+built-in called :func:`sum` to compute it:
+
+ >>> reduce(operator.add, [1,2,3,4], 0)
+ 10
+ >>> sum([1,2,3,4])
+ 10
+ >>> sum([])
+ 0
For many uses of :func:`reduce`, though, it can be clearer to just write the
obvious :keyword:`for` loop::
@@ -701,8 +721,11 @@
``enumerate(iter)`` counts off the elements in the iterable, returning 2-tuples
containing the count and each element. ::
- enumerate(['subject', 'verb', 'object']) =>
- (0, 'subject'), (1, 'verb'), (2, 'object')
+ >>> for item in enumerate(['subject', 'verb', 'object']):
+ ... print item
+ (0, 'subject')
+ (1, 'verb')
+ (2, 'object')
:func:`enumerate` is often used when looping through a list and recording the
indexes at which certain conditions are met::
@@ -712,20 +735,21 @@
if line.strip() == '':
print('Blank line at line #%i' % i)
-``sorted(iterable, [key=None], [reverse=False)`` collects all the elements of
-the iterable into a list, sorts the list, and returns the sorted result. The
-``key``, and ``reverse`` arguments are passed through to the constructed list's
-``sort()`` method. ::
- import random
- # Generate 8 random numbers between [0, 10000)
- rand_list = random.sample(range(10000), 8)
- rand_list =>
- [769, 7953, 9828, 6431, 8442, 9878, 6213, 2207]
- sorted(rand_list) =>
- [769, 2207, 6213, 6431, 7953, 8442, 9828, 9878]
- sorted(rand_list, reverse=True) =>
- [9878, 9828, 8442, 7953, 6431, 6213, 2207, 769]
+``sorted(iterable, [cmp=None], [key=None], [reverse=False)`` collects all the
+elements of the iterable into a list, sorts the list, and returns the sorted
+result. The ``cmp``, ``key``, and ``reverse`` arguments are passed through to
+the constructed list's ``.sort()`` method. ::
+
+ >>> import random
+ >>> # Generate 8 random numbers between [0, 10000)
+ >>> rand_list = random.sample(range(10000), 8)
+ >>> rand_list
+ [769, 7953, 9828, 6431, 8442, 9878, 6213, 2207]
+ >>> sorted(rand_list)
+ [769, 2207, 6213, 6431, 7953, 8442, 9828, 9878]
+ >>> sorted(rand_list, reverse=True)
+ [9878, 9828, 8442, 7953, 6431, 6213, 2207, 769]
(For a more detailed discussion of sorting, see the Sorting mini-HOWTO in the
Python wiki at http://wiki.python.org/moin/HowTo/Sorting.)
@@ -733,20 +757,20 @@
The ``any(iter)`` and ``all(iter)`` built-ins look at the truth values of an
iterable's contents. :func:`any` returns True if any element in the iterable is
a true value, and :func:`all` returns True if all of the elements are true
-values::
+values:
- any([0,1,0]) =>
- True
- any([0,0,0]) =>
- False
- any([1,1,1]) =>
- True
- all([0,1,0]) =>
- False
- all([0,0,0]) =>
- False
- all([1,1,1]) =>
- True
+ >>> any([0,1,0])
+ True
+ >>> any([0,0,0])
+ False
+ >>> any([1,1,1])
+ True
+ >>> all([0,1,0])
+ False
+ >>> all([0,0,0])
+ False
+ >>> all([1,1,1])
+ True
Small functions and the lambda expression
@@ -758,31 +782,31 @@
If there's a Python built-in or a module function that's suitable, you don't
need to define a new function at all::
- stripped_lines = [line.strip() for line in lines]
- existing_files = filter(os.path.exists, file_list)
+ stripped_lines = [line.strip() for line in lines]
+ existing_files = filter(os.path.exists, file_list)
If the function you need doesn't exist, you need to write it. One way to write
small functions is to use the ``lambda`` statement. ``lambda`` takes a number
of parameters and an expression combining these parameters, and creates a small
function that returns the value of the expression::
- lowercase = lambda x: x.lower()
+ lowercase = lambda x: x.lower()
- print_assign = lambda name, value: name + '=' + str(value)
+ print_assign = lambda name, value: name + '=' + str(value)
- adder = lambda x, y: x+y
+ adder = lambda x, y: x+y
An alternative is to just use the ``def`` statement and define a function in the
usual way::
- def lowercase(x):
- return x.lower()
+ def lowercase(x):
+ return x.lower()
- def print_assign(name, value):
- return name + '=' + str(value)
+ def print_assign(name, value):
+ return name + '=' + str(value)
- def adder(x,y):
- return x + y
+ def adder(x,y):
+ return x + y
Which alternative is preferable? That's a style question; my usual course is to
avoid using ``lambda``.
@@ -853,24 +877,20 @@
``itertools.count(n)`` returns an infinite stream of integers, increasing by 1
each time. You can optionally supply the starting number, which defaults to 0::
- itertools.count() =>
- 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ...
- itertools.count(10) =>
- 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, ...
+ itertools.count() =>
+ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ...
+ itertools.count(10) =>
+ 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, ...
``itertools.cycle(iter)`` saves a copy of the contents of a provided iterable
and returns a new iterator that returns its elements from first to last. The
-new iterator will repeat these elements infinitely.
+new iterator will repeat these elements infinitely. ::
-::
-
- itertools.cycle([1,2,3,4,5]) =>
- 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, ...
+ itertools.cycle([1,2,3,4,5]) =>
+ 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, ...
``itertools.repeat(elem, [n])`` returns the provided element ``n`` times, or
-returns the element endlessly if ``n`` is not provided.
-
-::
+returns the element endlessly if ``n`` is not provided. ::
itertools.repeat('abc') =>
abc, abc, abc, abc, abc, abc, abc, abc, abc, abc, ...
@@ -879,9 +899,7 @@
``itertools.chain(iterA, iterB, ...)`` takes an arbitrary number of iterables as
input, and returns all the elements of the first iterator, then all the elements
-of the second, and so on, until all of the iterables have been exhausted.
-
-::
+of the second, and so on, until all of the iterables have been exhausted. ::
itertools.chain(['a', 'b', 'c'], (1, 2, 3)) =>
a, b, c, 1, 2, 3
@@ -900,9 +918,7 @@
This iterator is intended to be used with iterables that are all of the same
length. If the iterables are of different lengths, the resulting stream will be
-the same length as the shortest iterable.
-
-::
+the same length as the shortest iterable. ::
itertools.izip(['a', 'b'], (1, 2, 3)) =>
('a', 1), ('b', 2)
@@ -916,9 +932,7 @@
first ``stop`` elements. If you supply a starting index, you'll get
``stop-start`` elements, and if you supply a value for ``step``, elements will
be skipped accordingly. Unlike Python's string and list slicing, you can't use
-negative values for ``start``, ``stop``, or ``step``.
-
-::
+negative values for ``start``, ``stop``, or ``step``. ::
itertools.islice(range(10), 8) =>
0, 1, 2, 3, 4, 5, 6, 7
@@ -932,9 +946,7 @@
If you don't supply a value for ``n``, the default is 2. Replicating iterators
requires saving some of the contents of the source iterator, so this can consume
significant memory if the iterator is large and one of the new iterators is
-consumed more than the others.
-
-::
+consumed more than the others. ::
itertools.tee( itertools.count() ) =>
iterA, iterB
@@ -1116,87 +1128,76 @@
The ``compose()`` function implements function composition. In other words, it
returns a wrapper around the ``outer`` and ``inner`` callables, such that the
-return value from ``inner`` is fed directly to ``outer``. That is,
+return value from ``inner`` is fed directly to ``outer``. That is, ::
-::
+ >>> def add(a, b):
+ ... return a + b
+ ...
+ >>> def double(a):
+ ... return 2 * a
+ ...
+ >>> compose(double, add)(5, 6)
+ 22
- >>> def add(a, b):
- ... return a + b
- ...
- >>> def double(a):
- ... return 2 * a
- ...
- >>> compose(double, add)(5, 6)
- 22
+is equivalent to ::
-is equivalent to
-
-::
-
- >>> double(add(5, 6))
- 22
+ >>> double(add(5, 6))
+ 22
The ``unpack`` keyword is provided to work around the fact that Python functions
are not always `fully curried <http://en.wikipedia.org/wiki/Currying>`__. By
default, it is expected that the ``inner`` function will return a single object
and that the ``outer`` function will take a single argument. Setting the
``unpack`` argument causes ``compose`` to expect a tuple from ``inner`` which
-will be expanded before being passed to ``outer``. Put simply,
+will be expanded before being passed to ``outer``. Put simply, ::
-::
-
- compose(f, g)(5, 6)
+ compose(f, g)(5, 6)
is equivalent to::
- f(g(5, 6))
+ f(g(5, 6))
-while
+while ::
-::
-
- compose(f, g, unpack=True)(5, 6)
+ compose(f, g, unpack=True)(5, 6)
is equivalent to::
- f(*g(5, 6))
+ f(*g(5, 6))
Even though ``compose()`` only accepts two functions, it's trivial to build up a
version that will compose any number of functions. We'll use ``functools.reduce()``,
``compose()`` and ``partial()`` (the last of which is provided by both
-``functional`` and ``functools``).
+``functional`` and ``functools``). ::
-::
-
- from functional import compose, partial
+ from functional import compose, partial
- multi_compose = partial(functools.reduce, compose)
+
+ multi_compose = partial(reduce, compose)
We can also use ``map()``, ``compose()`` and ``partial()`` to craft a version of
``"".join(...)`` that converts its arguments to string::
- from functional import compose, partial
+ from functional import compose, partial
- join = compose("".join, partial(map, str))
+ join = compose("".join, partial(map, str))
``flip(func)``
``flip()`` wraps the callable in ``func`` and causes it to receive its
-non-keyword arguments in reverse order.
+non-keyword arguments in reverse order. ::
-::
-
- >>> def triple(a, b, c):
- ... return (a, b, c)
- ...
- >>> triple(5, 6, 7)
- (5, 6, 7)
- >>>
- >>> flipped_triple = flip(triple)
- >>> flipped_triple(5, 6, 7)
- (7, 6, 5)
+ >>> def triple(a, b, c):
+ ... return (a, b, c)
+ ...
+ >>> triple(5, 6, 7)
+ (5, 6, 7)
+ >>>
+ >>> flipped_triple = flip(triple)
+ >>> flipped_triple(5, 6, 7)
+ (7, 6, 5)
``foldl(func, start, iterable)``
@@ -1207,35 +1208,34 @@
This means that a call such as::
- foldl(f, 0, [1, 2, 3])
+ foldl(f, 0, [1, 2, 3])
is equivalent to::
- f(f(f(0, 1), 2), 3)
+ f(f(f(0, 1), 2), 3)
``foldl()`` is roughly equivalent to the following recursive function::
- def foldl(func, start, seq):
- if len(seq) == 0:
- return start
+ def foldl(func, start, seq):
+ if len(seq) == 0:
+ return start
- return foldl(func, func(start, seq[0]), seq[1:])
+ return foldl(func, func(start, seq[0]), seq[1:])
Speaking of equivalence, the above ``foldl`` call can be expressed in terms of
the built-in ``reduce`` like so::
- reduce(f, [1, 2, 3], 0)
+ reduce(f, [1, 2, 3], 0)
We can use ``foldl()``, ``operator.concat()`` and ``partial()`` to write a
cleaner, more aesthetically-pleasing version of Python's ``"".join(...)``
idiom::
- from functional import foldl, partial
- from operator import concat
-
- join = partial(foldl, concat, "")
+ from functional import foldl, partial from operator import concat
+
+ join = partial(foldl, concat, "")
Revision History and Acknowledgements