[Python-ideas] Generators are iterators

Steven D'Aprano steve at pearwood.info
Thu Dec 11 01:30:32 CET 2014

On Wed, Dec 10, 2014 at 05:11:43PM -0500, Alexander Belopolsky wrote:

> I think the problem is with the term "generator function" because what we
> call "generator function" is neither a generator nor a function.

I'm afraid that is just wrong. "Generator functions" are functions.

py> def gen():
...     yield 1
py> type(gen)
<class 'function'>

They are distinguishable from other functions by the presence of a flag 
on the __code__ object. The ``isgeneratorfunction`` function in the 
inspect module is short enough to reproduce here:

def isgeneratorfunction(object):
    """Return true if the object is a user-defined generator function.

    Generator function objects provides same attributes as functions.

    See help(isfunction) for attributes listing."""
    return bool((isfunction(object) or ismethod(object)) and
                object.__code__.co_flags & CO_GENERATOR)

Generator functions are essentially syntactic sugar for building 
iterators from coroutines. The specific type of iterator they return is 
a generator, which is a built-in type (but not a built-in name).


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