Python iter() built-in function
From the Python 3 documentation
Return an iterator object. The first argument is interpreted very differently depending on the presence of the second argument. Without a second argument, object must be a collection object which supports the iterable protocol, or it must support the sequence protocol. If it does not support either of those protocols, TypeError is raised.
Introduction
The iter() function returns an iterator object. An iterator is an object that can be iterated (looped) upon. It’s what powers for loops in Python.
You can use iter() to get an iterator from any iterable object, like a list, tuple, or string.
Examples
Getting an iterator from a list:
my_list = [1, 2, 3]
my_iter = iter(my_list)
print(next(my_iter)) # Output: 1
print(next(my_iter)) # Output: 2
print(next(my_iter)) # Output: 3
>>> i = iter([1, 2, 3])
>>> i
# <list_iterator object at 0x7f93158badc0>
>>> i.__next__()
# 1
>>> i.__next__()
# 2
>>> i.__next__()
# 3