当使用for循环迭代时，我如何处理输入的最后一个元素?特别是，如果有代码应该只出现在元素之间(而不是在最后一个元素之后)，我该如何构造代码?
目前，我写的代码是这样的:
for i, data in enumerate(data_list):
code_that_is_done_for_every_element
if i != len(data_list) - 1:
code_that_is_done_between_elements
我如何简化或改进它?
当前回答
除了向上数，你也可以向下数:
nrToProcess = len(list)
for s in list:
s.doStuff()
nrToProcess -= 1
if nrToProcess==0: # this is the last one
s.doSpecialStuff()
其他回答
假设input是一个迭代器，下面是使用itertools中的tee和izip的方法:
from itertools import tee, izip
items, between = tee(input_iterator, 2) # Input must be an iterator.
first = items.next()
do_to_every_item(first) # All "do to every" operations done to first item go here.
for i, b in izip(items, between):
do_between_items(b) # All "between" operations go here.
do_to_every_item(i) # All "do to every" operations go here.
演示:
>>> def do_every(x): print "E", x
...
>>> def do_between(x): print "B", x
...
>>> test_input = iter(range(5))
>>>
>>> from itertools import tee, izip
>>>
>>> items, between = tee(test_input, 2)
>>> first = items.next()
>>> do_every(first)
E 0
>>> for i,b in izip(items, between):
... do_between(b)
... do_every(i)
...
B 0
E 1
B 1
E 2
B 2
E 3
B 3
E 4
>>>
我发现在循环表达式之前定义循环值很方便。对于这个方框示例，匹配循环中的值，或者其他可能需要它的地方。
numberofboxes = 1411
for j in range(1,numberofboxes):
if j != numberofboxes - 1:
print ("},")
else:
print("}")
我想到的一个简单的解决办法是:
for i in MyList:
# Check if 'i' is the last element in the list
if i == MyList[-1]:
# Do something different for the last
else:
# Do something for all other elements
第二个同样简单的解决方法是使用计数器:
# Count the no. of elements in the list
ListLength = len(MyList)
# Initialize a counter
count = 0
for i in MyList:
# increment counter
count += 1
# Check if 'i' is the last element in the list
# by using the counter
if count == ListLength:
# Do something different for the last
else:
# Do something for all other elements
你可以用下面的代码确定最后一个元素:
for i,element in enumerate(list):
if (i==len(list)-1):
print("last element is" + element)
如果项目是唯一的:
for x in list:
#code
if x == list[-1]:
#code
其他选项:
pos = -1
for x in list:
pos += 1
#code
if pos == len(list) - 1:
#code
for x in list:
#code
#code - e.g. print x
if len(list) > 0:
for x in list[:-1]:
#process everything except the last element
for x in list[-1:]:
#process only last element
