Python in a Nutshell

Name

iter

Synopsis

iter(obj)iter(func,sentinel)

Creates and returns an iterator: an object with a next method that you can call repeatedly to get one item at a time (see Section 4.9.3.1 in Chapter 4). When called with one argument, iter( obj ) normally returns obj .__iter__( ). When obj is a sequence without a special method __iter__, iter( obj ) is equivalent to the following simple generator:

def iterSequence(obj):
    i = 0
    while 1:
        try: yield obj[i]
        except IndexError: raise StopIteration
        i += 1

See also Section 4.10.8 in Chapter 4 and __iter__ in Chapter 5.

When called with two arguments, the first argument must be callable without arguments, and iter( func,sentinel ) is equivalent to the following simple generator:

def iterSentinel(func, sentinel):
    while 1:
        item = func( )
        if item =  = sentinel: raise StopIteration
        yield item

As discussed in Chapter 4, the statement for x in obj is equivalent to for x in iter( obj ). iter is idempotent. In other words, when x is an iterator, iter( x ) is x, as long as x supplies an __iter__ method whose body is just return self, as an iterator should.