虽然Python文档说这enumerate在功能上等同于：
def enumerate(sequence, start=0):
n = start
for elem in sequence:
yield n, elem
n += 1
实enumerate函数返回 ，但不返回实际生成器。help(x)创建enumerate对象后调用可以看到以下内容：
>>> x = enumerate([1,2])
>>> help(x)
class enumerate(object)
| enumerate(iterable[, start]) -> iterator for index, value of iterable
|
| Return an enumerate object. iterable must be another object that supports
| iteration. The enumerate object yields pairs containing a count (from
| start, which defaults to zero) and a value yielded by the iterable argument.
| enumerate is useful for obtaining an indexed list:
| (0, seq[0]), (1, seq[1]), (2, seq[2]), ...
|
| Methods defined here:
|
| __getattribute__(...)
| x.__getattribute__('name') <==> x.name
|
| __iter__(...)
| x.__iter__() <==> iter(x)
|
| next(...)
| x.next() -> the next value, or raise StopIteration
|
| ----------------------------------------------------------------------
| Data and other attributes defined here:
|
| __new__ = <built-in method __new__ of type object>
| T.__new__(S, ...) -> a new object with type S, a subtype of T
在Python中，生成器基本上是一种特定类型的迭代器，通过使用ayield从函数返回数据来实现。但是，enumerate实际上是用C而不是纯Python实现的，因此没有yield涉及。您可以在此处找到源：http ://hg.python.org/cpython/file/2.7/Objects/enumobject.c
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