1、reversed
2、enumerate
(1) enumerate() description
- Enumerate means enumeration and enumeration in the dictionary
- For an iterable/traversable object (such as a list, a string), enumerate will form an index sequence, which can be used to get the index and value at the same time
- enumerate is mostly used to get counts in for loops
For example, for a seq, we get:
(0, seq[0]), (1, seq[1]), (2, seq[2])
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- enumerate() returns an enumerate object, for example:
(2) use of enumerate
- If you want to traverse both the index and the elements of a list, you can first write this:
list1 = ["这", "是", "一个", "测试"]
for i in range (len(list1)):
print i ,list1[i]
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- The above method is a bit cumbersome, using enumerate() will be more direct and elegant:
list1 = ["这", "是", "一个", "测试"]
for index, item in enumerate(list1):
print index, item
>>>
0 这
1 是
2 一个
3 测试
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- enumerate can also receive a second parameter, which is used to specify the starting value of the index, such as:
list1 = ["这", "是", "一个", "测试"]
for index, item in enumerate(list1, 1):
print index, item
>>>
1 这
2 是
3 一个
4 测试
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(3) Supplement
If you want to count the number of lines in a file, you can write:
count = len(open(filepath, 'r').readlines())
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This method is simple, but can be slow and doesn't even work when the file size is large .
You can use enumerate():
count = 0
for index, line in enumerate(open(filepath,'r')):
count += 1