itertools

This is the observed behavior: In [4]: x = itertools.groupby(range(10), lambda x: True) In [5]: y = next(x) In [6]: next(x) --------------------------------------------------------------------------- StopIteration Traceback (most recent call last) <ipython-input-6-5e4e57af3a97> in <module>() ----> 1 next(x) StopIteration: In [7]: y Out[7]: (True, <itertools._grouper at 0x10a672e80>) In [8]: list(y[1]) Out[8]: [9] The expected output of list(y[1]) is [0,1,2,3,4,5,6,7,8,9] What's going on here? I observed this on cpython 3.4.2 , but others have seen this with cpython 3.5 and IronPython 2.9.9a0

I am new to Python. I am trying to import izip_longest from itertools. But I am not able to find the import "itertools" in the preferences in Python interpreter. I am using Python 3.5.2. It gives me the below error- from itertools import izip_longest ImportError: cannot import name 'izip_longest' Please let me know what is the right course of action. I have tried Python 2.7 too and ended up with same problem. Do I need to use lower version Python. Martijn Pieters izip_longest was renamed to zip_longest in Python 3 (note, no i at the start), import that instead: from itertools import zip

In the context of a discussion in the comments of this question it was mentioned that while concatenating a sequence of strings simply takes ''.join([str1, str2, ...]) , concatenating a sequence of lists would be something like list(itertools.chain(lst1, lst2, ...)) , although you can also use a list comprehension like [x for y in [lst1, lst2, ...] for x in y] . What surprised me is that the first method is consistently faster than the second: import random import itertools random.seed(100) lsts = [[1] * random.randint(100, 1000) for i in range(1000)] %timeit [x for y in lsts for x in y] # 39

Given a string, I want to generate all possible combinations. In other words, all possible ways of putting a comma somewhere in the string. For example: input: ["abcd"] output: ["abcd"] ["abc","d"] ["ab","cd"] ["ab","c","d"] ["a","bc","d"] ["a","b","cd"] ["a","bcd"] ["a","b","c","d"] I am a bit stuck on how to generate all the possible lists. Combinations will just give me lists with length of subset of the set of strings, permutations will give all possible ways to order. I can make all the cases with only one comma in the list because of iterating through the slices, but I can't make cases

In Python 3.3, itertools.accumulate() , which normally repeatedly applies an addition operation to the supplied iterable, can now take a function argument as a parameter; this means it now overlaps with functools.reduce() . With a cursory look, the main differences between the two now would seem to be: accumulate() defaults to summing but doesn't let you supply an extra initial condition explicitly while reduce() doesn't default to any method but does let you supply an initial condition for use with 1/0-element sequences, and accumulate() takes the iterable first while reduce() takes the

I have a relatively large (1 GB) text file that I want to cut down in size by summing across categories: Geography AgeGroup Gender Race Count County1 1 M 1 12 County1 2 M 1 3 County1 2 M 2 0 To: Geography Count County1 15 County2 23 This would be a simple matter if the whole file could fit in memory but using pandas.read_csv() gives MemoryError . So I have been looking into other methods, and there appears to be many options - HDF5? Using itertools (which seems complicated - generators?) Or just using the standard file methods to read in the first geography (70 lines), sum the count column,