確定你在python循環中的哪個迭代

Question

基本上我想能夠告訴我什麼時候在循環迭代中的第N個項目。 有什麼想法？

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

使用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

如何使用enumerate？

>>> 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 

Answer 3

for x in d.keys()[:-1]: 
    print x 
if d: print "last item:", d.keys()[-1] 

Answer 4

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

for i,x in enumerate(d): 
    print "last item :"+repr(x) if i+1==len(d) else x 

但無序字典的最後一個項目並不意味着什麼

Answer 5

list = [1,2,3] 

last = list[-1] 

for i in list: 
    if i == last: 
     print("Last:") 
    print i 

輸出：

1 
2 
Last: 
3