49 lines
909 B
Python
49 lines
909 B
Python
#!/usr/bin/env python
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# -*- encoding: utf-8 -*-
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"""
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Topic: 方向迭代
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Desc :
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"""
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def reverse_iterate():
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a = [1, 2, 3, 4]
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for x in reversed(a):
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print(x)
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# 两个条件：大小可知或者实现__reversed__方法，
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# 如果都不满足，先转换为list
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# Print a file backwards
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# f = open('somefile')
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# for line in reversed(list(f)):
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# print(line, end='')
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for rr in reversed(Countdown(30)):
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print(rr)
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for rr in Countdown(30):
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print(rr)
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class Countdown:
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def __init__(self, start):
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self.start = start
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# Forward iterator
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def __iter__(self):
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n = self.start
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while n > 0:
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yield n
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n -= 1
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# Reverse iterator
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def __reversed__(self):
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n = 1
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while n <= self.start:
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yield n
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n += 1
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if __name__ == '__main__':
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reverse_iterate()
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