documentation for lazy for-comprehensions in Python

Question

It looks like this construct in Python is not lazy:

g1 = ["'"+x+"'" for x in f2]

and this one is:

g2 = ("'"+x+"'" for x in f2)

since g2 has a next() method and g1 does not.

Where is this documented? I can't seem to find the relevant page in the python docs, not sure what to look up.

Answer 1

You are looking for list displays and generator expressions. The first form is called a "list comprehension", and is a specialized form of defining a list.

As for the second form, the generator expression, this is what the documentation has to say:

A generator expression yields a new generator object. Its syntax is the same as for comprehensions, except that it is enclosed in parentheses instead of brackets or curly braces.