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<H2><A NAME="SECTION0071420000000000000000"><!--x--></A><A NAME="itertools-example"><!--z--></A>
<BR>
5.14.2 Examples
</H2>
<P>
The following examples show common uses for each tool and
demonstrate ways they can be combined.
<P>
<div class="verbatim"><pre>
>>> 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(1,4), repeat(3)):
... print cube
...
1
8
27
>>> reportlines = ['EuroPython', 'Roster', '', 'alex', '', 'laura',
'', 'martin', '', 'walter', '', 'samuele']
>>> for name in islice(reportlines, 3, None, 2):
... print name.title()
...
Alex
Laura
Martin
Walter
Samuele
</pre></div>
<P>
This section shows how itertools can be combined to create other more
powerful itertools. Note that <tt class="function">enumerate()</tt> and <tt class="method">iteritems()</tt>
already have efficient implementations in Python. They are only included here
to illustrate how higher level tools can be created from building blocks.
<P>
<div class="verbatim"><pre>
def take(n, seq):
return list(islice(seq, n))
def enumerate(iterable):
return izip(count(), iterable)
def tabulate(function):
"Return function(0), function(1), ..."
return imap(function, count())
def iteritems(mapping):
return izip(mapping.iterkeys(), mapping.itervalues())
def nth(iterable, n):
"Returns the nth item"
return list(islice(iterable, n, n+1))
def all(seq, pred=bool):
"Returns True if pred(x) is True for every element in the iterable"
return False not in imap(pred, seq)
def any(seq, pred=bool):
"Returns True if pred(x) is True at least one element in the iterable"
return True in imap(pred, seq)
def no(seq, pred=bool):
"Returns True if pred(x) is False for every element in the iterable"
return True not in imap(pred, seq)
def quantify(seq, pred=bool):
"Count how many times the predicate is True in the sequence"
return sum(imap(pred, seq))
def padnone(seq):
"Returns the sequence elements and then returns None indefinitely"
return chain(seq, repeat(None))
def ncycles(seq, n):
"Returns the sequence elements n times"
return chain(*repeat(seq, n))
def dotproduct(vec1, vec2):
return sum(imap(operator.mul, vec1, vec2))
def window(seq, n=2):
"Returns a sliding window (of width n) over data from the iterable"
" s -> (s0,s1,...s[n-1]), (s1,s2,...,sn), ... "
it = iter(seq)
result = tuple(islice(it, n))
if len(result) == n:
yield result
for elem in it:
result = result[1:] + (elem,)
yield result
def tee(iterable):
"Return two independent iterators from a single iterable"
def gen(next, data={}, cnt=[0]):
dpop = data.pop
for i in count():
if i == cnt[0]:
item = data[i] = next()
cnt[0] += 1
else:
item = dpop(i)
yield item
next = iter(iterable).next
return (gen(next), gen(next))
</pre></div>
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<span class="release-info">Release 2.3.4, documentation updated on May 20, 2004.</span>
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