Is there a library function in Python to turn a generator-function into a function returning a list?

Question

A number of times I've thought that generator style can be more direct that returning a list, for example,

def foo(input_array):     for x in input_array:         yield processed(x) 

vs.

def bar(input_array):     accumulator = []     for x in input_array:         accumulator.append(processed(x))     return accumulator 

(okay, if it were really that simple, I'd write map, but you get the point: the generator version is cleaner). However, a return type of a generator is not always desired. Is there a built-in decorator that I can use to change foo into a function returning a list or tuple? The way I'd write it myself is,

import functools  def transform_return_value(transformer):     def inner(f):         @functools.wraps(f)         def new_f(*argv, **kwargs):             return transformer(f(*argv, **kwargs))         return new_f     return inner  @transform_return_value(list) def foo(input_array):     for x in input_array:         yield processed(x) 

Answer 1

To the best of my knowledge (and I've looked, because I've wondered exactly the same thing), no: there is no direct way of doing this with the standard library.

There is a thoroughly tested listify wrapper in unstdlib.py library, though: https://github.com/shazow/unstdlib.py/blob/master/unstdlib/standard/list_.py#L149

def listify(fn=None, wrapper=list):     """     A decorator which wraps a function's return value in ``list(...)``.      Useful when an algorithm can be expressed more cleanly as a generator but     the function should return an list.      Example::          >>> @listify         ... def get_lengths(iterable):         ...     for i in iterable:         ...         yield len(i)         >>> get_lengths(["spam", "eggs"])         [4, 4]         >>>         >>> @listify(wrapper=tuple)         ... def get_lengths_tuple(iterable):         ...     for i in iterable:         ...         yield len(i)         >>> get_lengths_tuple(["foo", "bar"])         (3, 3)     """     def listify_return(fn):         @wraps(fn)         def listify_helper(*args, **kw):             return wrapper(fn(*args, **kw))         return listify_helper     if fn is None:         return listify_return     return listify_return(fn)