Is there an expression for an infinite iterator?

Is there a straight-forward expression that can produce an infinite iterator?

This is a purely theoretical question. No need for a "practical" answer here :)

For example, it is easy to use a generator expression to make a finite iterator:

my_gen = (0 for i in xrange(42))

However, to make an infinite one I need to "pollute" my namespace with a bogus function:

def _my_gen():
    while True:
        yield 0
my_gen = _my_gen()

Doing things in a separate file and import-ing later doesn't count.

I also know that itertools.repeat does exactly this. I'm curious if there is a one-liner solution without that.

itertools provides three infinite iterators:

• count(start=0, step=1): 0, 1, 2, 3, 4, ...

• cycle(p): p[0], p[1], ..., p[-1], p[0], ...

• repeat(x, times=∞): x, x, x, x, ...

I don't know of any others in the standard library.

Since you asked for a one-liner:

__import__("itertools").count()

for x in iter(int, 1): pass

• Two-argument iter = zero-argument callable + sentinel value
• int() always returns 0

Therefore, iter(int, 1) is an infinite iterator. There are obviously a huge number of variations on this particular theme (especially once you add lambda into the mix). One variant of particular note is iter(f, object()), as using a freshly created object as the sentinel value almost guarantees an infinite iterator regardless of the callable used as the first argument.

you can iterate over a callable returning a constant always different than iter()'s sentinel

g1=iter(lambda:0, 1)

Your OS may provide something that can be used as an infinite generator. Eg on linux

for i in (0 for x in open('/dev/urandom')):
    print i

obviously this is not as efficient as

for i in __import__('itertools').repeat(0)
    print i