Python: generator expression vs. yield

Question

In Python, is there any difference between creating a generator object through a generator expression versus using the yield statement?

Answer 1

In usage, note a distinction between a generator object vs a generator function.

A generator object is use-once-only, in contrast to a generator function, which can be reused each time you call it again, because it returns a fresh generator object.

Generator expressions are in practice usually used "raw", without wrapping them in a function, and they return a generator object.

E.g.:

def range_10_gen_func():
    x = 0
    while x < 10:
        yield x
        x = x + 1

print(list(range_10_gen_func()))
print(list(range_10_gen_func()))
print(list(range_10_gen_func()))

which outputs:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Compare with a slightly different usage:

range_10_gen = range_10_gen_func()
print(list(range_10_gen))
print(list(range_10_gen))
print(list(range_10_gen))

which outputs:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[]
[]

And compare with a generator expression:

range_10_gen_expr = (x for x in range(10))
print(list(range_10_gen_expr))
print(list(range_10_gen_expr))
print(list(range_10_gen_expr))

which also outputs:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[]
[]