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Where is the source code for Python itertools.islice?

Where is the source code for Python itertools.islice?

I found itertoolsmodule.c, but can't find the function itertools.islice (maybe it's there, but I don't know much about C code).

I would like to understand what happens when I do:

itertools.islice(spamreader, rowStart, rowFinish+1)
Solution

  • You are looking at the old SVN repository; Python has since moved to mercurial. I'd look at he 2.7 version of itertoolsmodule.c; the source has an islice object.

    When you call itertools.islice() you create a new instance of that object, so islice_new is called.

    With 3 arguments, next in the C struct is set to int(rowStart), stop to int(rowFinish+1). step is left as None, it is set to iter(spamreader). Most importantly, cnt is set to 0. Then the object is returned.

    All the iteration work is done in islice_next(), where it is iterated over according to the next, stop and step values.

    cnt is incremented and next(it) is called as needed to advance the object until cnt is equal or greater to next; after that, for each call to islice_next() an item is yielded while cnt and next are incremented until stop is reached.