[Python-checkins] r61261 - python/trunk/Doc/library/itertools.rst
raymond.hettinger
python-checkins at python.org
Thu Mar 6 02:15:52 CET 2008
Author: raymond.hettinger
Date: Thu Mar 6 02:15:52 2008
New Revision: 61261
Modified:
python/trunk/Doc/library/itertools.rst
Log:
Add examples.
Modified: python/trunk/Doc/library/itertools.rst
==============================================================================
--- python/trunk/Doc/library/itertools.rst (original)
+++ python/trunk/Doc/library/itertools.rst Thu Mar 6 02:15:52 2008
@@ -71,6 +71,7 @@
Equivalent to::
def chain(*iterables):
+ # chain('ABC', 'DEF') --> A B C D E F
for it in iterables:
for element in it:
yield element
@@ -83,6 +84,7 @@
@classmethod
def from_iterable(iterables):
+ # chain.from_iterable(['ABC', 'DEF']) --> A B C D E F
for it in iterables:
for element in it:
yield element
@@ -108,7 +110,8 @@
Equivalent to::
def combinations(iterable, r):
- 'combinations(range(4), 3) --> (0,1,2) (0,1,3) (0,2,3) (1,2,3)'
+ # combinations('ABCD', 2) --> AB AC AD BC BD CD
+ # combinations(range(4), 3) --> 012 013 023 123
pool = tuple(iterable)
n = len(pool)
indices = range(r)
@@ -145,6 +148,7 @@
numbers. Equivalent to::
def count(n=0):
+ # count(10) --> 10 11 12 13 14 ...
while True:
yield n
n += 1
@@ -157,6 +161,7 @@
indefinitely. Equivalent to::
def cycle(iterable):
+ # cycle('ABCD') --> A B C D A B C D A B C D ...
saved = []
for element in iterable:
yield element
@@ -177,6 +182,7 @@
start-up time. Equivalent to::
def dropwhile(predicate, iterable):
+ # dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 4 1
iterable = iter(iterable)
for x in iterable:
if not predicate(x):
@@ -215,6 +221,8 @@
:func:`groupby` is equivalent to::
class groupby(object):
+ # [k for k, g in groupby('AAAABBBCCDAABBB')] --> A B C D A B
+ # [(list(g)) for k, g in groupby('AAAABBBCCD')] --> AAAA BBB CC D
def __init__(self, iterable, key=None):
if key is None:
key = lambda x: x
@@ -245,6 +253,7 @@
that are true. Equivalent to::
def ifilter(predicate, iterable):
+ # ifilter(lambda x: x%2, range(10)) --> 1 3 5 7 9
if predicate is None:
predicate = bool
for x in iterable:
@@ -259,6 +268,7 @@
that are false. Equivalent to::
def ifilterfalse(predicate, iterable):
+ # ifilterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8
if predicate is None:
predicate = bool
for x in iterable:
@@ -277,6 +287,7 @@
useful way of supplying arguments to :func:`imap`. Equivalent to::
def imap(function, *iterables):
+ # imap(pow, (2,3,10), (5,2,3)) --> 32 9 1000
iterables = map(iter, iterables)
while True:
args = [it.next() for it in iterables]
@@ -299,6 +310,10 @@
multi-line report may list a name field on every third line). Equivalent to::
def islice(iterable, *args):
+ # islice('ABCDEFG', 2) --> A B
+ # islice('ABCDEFG', 2, 4) --> C D
+ # islice('ABCDEFG', 2, None) --> C D E F G
+ # islice('ABCDEFG', 0, None, 2) --> A C E G
s = slice(*args)
it = iter(xrange(s.start or 0, s.stop or sys.maxint, s.step or 1))
nexti = it.next()
@@ -321,6 +336,7 @@
lock-step iteration over several iterables at a time. Equivalent to::
def izip(*iterables):
+ # izip('ABCD', 'xy') --> Ax By
iterables = map(iter, iterables)
while iterables:
result = [it.next() for it in iterables]
@@ -346,6 +362,7 @@
Iteration continues until the longest iterable is exhausted. Equivalent to::
def izip_longest(*args, **kwds):
+ # izip_longest('ABCD', 'xy', fillvalue='-') --> Ax By C- D-
fillvalue = kwds.get('fillvalue')
def sentinel(counter = ([fillvalue]*(len(args)-1)).pop):
yield counter() # yields the fillvalue, or raises IndexError
@@ -382,7 +399,8 @@
Equivalent to::
def permutations(iterable, r=None):
- 'permutations(range(3), 2) --> (0,1) (0,2) (1,0) (1,2) (2,0) (2,1)'
+ # permutations('ABCD', 2) --> AB AC AD BA BC BD CA CB CD DA DB DC
+ # permutations(range(3)) --> 012 021 102 120 201 210
pool = tuple(iterable)
n = len(pool)
r = n if r is None else r
@@ -424,8 +442,8 @@
Equivalent to nested for-loops in a generator expression. For example,
``product(A, B)`` returns the same as ``((x,y) for x in A for y in B)``.
- The leftmost iterators are in the outermost for-loop, so the output tuples
- cycle like an odometer (with the rightmost element changing on every
+ The leftmost iterators correspond to the outermost for-loop, so the output
+ tuples cycle like an odometer (with the rightmost element changing on every
iteration). This results in a lexicographic ordering so that if the
inputs iterables are sorted, the product tuples are emitted
in sorted order.
@@ -438,6 +456,8 @@
actual implementation does not build up intermediate results in memory::
def product(*args, **kwds):
+ # product('ABCD', 'xy') --> Ax Ay Bx By Cx Cy Dx Dy
+ # product(range(2), repeat=3) --> 000 001 010 011 100 101 110 111
pools = map(tuple, args) * kwds.get('repeat', 1)
result = [[]]
for pool in pools:
@@ -451,10 +471,11 @@
Make an iterator that returns *object* over and over again. Runs indefinitely
unless the *times* argument is specified. Used as argument to :func:`imap` for
- invariant parameters to the called function. Also used with :func:`izip` to
- create an invariant part of a tuple record. Equivalent to::
+ invariant function parameters. Also used with :func:`izip` to create constant
+ fields in a tuple record. Equivalent to::
def repeat(object, times=None):
+ # repeat(10, 3) --> 10 10 10
if times is None:
while True:
yield object
@@ -472,6 +493,7 @@
between ``function(a,b)`` and ``function(*c)``. Equivalent to::
def starmap(function, iterable):
+ # starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 9 1000
for args in iterable:
yield function(*args)
@@ -485,6 +507,7 @@
predicate is true. Equivalent to::
def takewhile(predicate, iterable):
+ # takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4
for x in iterable:
if predicate(x):
yield x
@@ -528,23 +551,6 @@
The following examples show common uses for each tool and demonstrate ways they
can be combined. ::
- >>> amounts = [120.15, 764.05, 823.14]
- >>> for checknum, amount in izip(count(1200), amounts):
- ... print 'Check %d is for $%.2f' % (checknum, amount)
- ...
- Check 1200 is for $120.15
- Check 1201 is for $764.05
- Check 1202 is for $823.14
-
- >>> import operator
- >>> for cube in imap(operator.pow, xrange(1,5), repeat(3)):
- ... print cube
- ...
- 1
- 8
- 27
- 64
-
# Show a dictionary sorted and grouped by value
>>> from operator import itemgetter
>>> d = dict(a=1, b=2, c=1, d=2, e=1, f=2, g=3)
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