calling a function in a comprehension

[Skaperen]

is there any chance foo() could be called more than once or is it well defined to be exactly once in this or any other comprehension construct?

    a=[bar(x) for x in foo(x)]

[gontajones]

foo() will be called just at the beginning of the for loop.

def bar(n):
     return '0'+str(n)
def foo(n):
     return range(n)
print([bar(x) for x in foo(10)])