在python的循环中确定您正在进行的迭代

Question

基本上我希望能够在循环迭代中告诉我何时在第N个项目上.有什么想法吗？

d = {1:2, 3:4, 5:6, 7:8, 9:0}

for x in d:
    if last item: # <-- this line is psuedo code
        print "last item :", x
    else:
        print x

Answer 1

用途enumerate:

#!/usr/bin/env python

d = {1:2, 3:4, 5:6, 7:8, 9:0}

# If you want an ordered dictionary (and have python 2.7/3.2), 
# uncomment the next lines:

# from collections import OrderedDict
# d = OrderedDict(sorted(d.items(), key=lambda t: t[0]))

last = len(d) - 1

for i, x in enumerate(d):
    if i == last:
        print i, x, 'last'
    else:
        print i, x

# Output:
# 0 1
# 1 3
# 2 9
# 3 5
# 4 7 last

Answer 2

使用enumerate怎么样？

>>> d = {1:2, 3:4, 5:6, 7:8, 9:0}
>>> for i, v in enumerate(d):
...     print i, v              # i is the index
... 
0 1
1 3
2 9
3 5
4 7