Python中enumerate的用法

Python中enumerate的用法：

>>> seasons = ['Spring', 'Summer', 'Fall', 'Winter']
>>> list(enumerate(seasons))
[(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]
>>> list(enumerate(seasons, start=1))
[(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')]

def enumerate(sequence, start=0):
    n = start
    for elem in sequence:
        yield n, elem
        n += 1