Feature Requests item #1726707, was opened at 2007-05-27 23:51
Message generated for change (Comment added) made by rhettinger
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Category: None
Group: None
>Status: Closed
>Resolution: Rejected
Priority: 5
Private: No
Submitted By: paul rubin (phr)
Assigned to: Nobody/Anonymous (nobody)
Summary: add itertools.ichain function and count.getvalue
Initial Comment:
def ichain(seq):
for s in seq:
for t in s: yield t
This is like itertools.chain except seq is lazy-evaluated element-by-element.
Obvious use cases:
# equivalent of perl's "while (<>) { ... } "
for line in ichain(all_lines_of(f) for f in list_of_filenames):
do_something_with(line)
# generate infinite sequence 1,1,1,2,2,2...
seq = ichain(repeat(i,3) for i in count(1))
Also requested: it would be nice to be able to get the current counter value
from a count() instance without incrementing it, e.g.
c = count()
...
i = c.getvalue()
This is clearly useful since repr(c) does something like that internally.
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>Comment By: Raymond Hettinger (rhettinger)
Date: 2007-05-28 00:15
Message:
Logged In: YES
user_id=80475
Originator: NO
Am rejecting ichain() because it adds too little in the way of
functionality to be worth the confusion associated with having two like
named functions and two ways to handle most problems.
Also, I think that some the use cases for lazy-evaluated inputs are better
served by using explicit for-loops and not itertools (too much magic
underneath the hood). I do see some value in having lazy-evaluated inputs
but do not think it is worth complexifying the module any further.
FWIW, the first example has no need for lazy evaluation. I would write it
as:
for line in chain(*map(open, list_of_filenames)):
do_something_with(line)
Or, just use plain vanilla Python:
for filename in list_of_filenames:
for line in open(filename):
do_something_with(line)
Please submit a separate feature request for count.getvalue(). I'm
thinking it should be a read-only attribute instead of a method. The only
downside is that it complicates the explanation of an otherwise trivially
simple tool.
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