Update itertools recipes.

This commit is contained in:
Raymond Hettinger 2010-03-28 18:29:17 +00:00
parent 9b0e9180e2
commit af9ab377d3
1 changed files with 40 additions and 8 deletions

View File

@ -580,16 +580,19 @@ which incur interpreter overhead.
"Return first n items of the iterable as a list"
return list(islice(iterable, n))
def enumerate(iterable, start=0):
return zip(count(start), iterable)
def tabulate(function, start=0):
"Return function(0), function(1), ..."
return map(function, count(start))
def consume(iterator, n):
"Advance the iterator n-steps ahead. If n is none, consume entirely."
collections.deque(islice(iterator, n), maxlen=0)
# Use functions that consume iterators at C speed.
if n is None:
# feed the entire iterator into a zero-length deque
collections.deque(iterator, maxlen=0)
else:
# advance to the emtpy slice starting at position n
next(islice(iterator, n, n), None)
def nth(iterable, n, default=None):
"Returns the nth item or a default value"
@ -661,10 +664,9 @@ which incur interpreter overhead.
seen = set()
seen_add = seen.add
if key is None:
for element in iterable:
if element not in seen:
seen_add(element)
yield element
for element in filterfalse(seen.__contains__, iterable):
seen_add(element)
yield element
else:
for element in iterable:
k = key(element)
@ -677,3 +679,33 @@ which incur interpreter overhead.
# unique_justseen('AAAABBBCCDAABBB') --> A B C D A B
# unique_justseen('ABBCcAD', str.lower) --> A B C A D
return map(next, map(itemgetter(1), groupby(iterable, key)))
def iter_except(func, exception, first=None):
""" Call a function repeatedly until an exception is raised.
Converts a call-until-exception interface to an iterator interface.
Like __builtin__.iter(func, sentinel) but uses an exception instead
of a sentinel to end the loop.
Examples:
iter_except(functools.partial(heappop, h), IndexError) # priority queue iterator
iter_except(d.popitem, KeyError) # non-blocking dict iterator
iter_except(d.popleft, IndexError) # non-blocking deque iterator
iter_except(q.get_nowait, Queue.Empty) # loop over a producer Queue
iter_except(s.pop, KeyError) # non-blocking set iterator
"""
try:
if first is not None:
yield first() # For database APIs needing an initial cast to db.first()
while 1:
yield func()
except exception:
pass
Note, many of the above recipes can be optimized by replacing global lookups
with local variables defined as default values. For example, the
*dotproduct* recipe can be written as::
def dotproduct(vec1, vec2, sum=sum, map=map, mul=operator.mul):
return sum(map(mul, vec1, vec2))