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Commit 7e1e2a0

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add 04-generator-and-iterator README.md 💥
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‎04-generator-and-iterator/README.md‎

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1. `demo.py`:支持迭代的类,正向迭代与反向迭代
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2. `genitor.py`:生成器的类,用于迭代
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3. `iterator_visit.py`:迭代器的访问:如`islice`访问生成器指定起始和终止点,跳过指定位置的元素,元素的排列组合,迭代添加索引,同时迭代多个序列,`zip`合并序列的访问,`chain`不同数据在一起迭代访问,将列表展平

‎04-generator-and-iterator/genitor.py‎

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class linehistory:
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def __init__(self, lines, histlen=3):
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self.lines = lines
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self.history = deque(maxlen=histlen)
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def __iter__(self):
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# 索引从 1 开始
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for lineno, line in enumerate(self.lines, 1):
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self.history.append((lineno, line))
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yield line
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def clear(self):
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self.history.clear()
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yield lineno, line
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# 创建一个实例对象,可以访问内部属性值
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# 如果你在迭代操作时不使用for循环语句,那么你得先调用 iter() 函数
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with open('demo.py') as f:
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with open('demo.py', encoding='utf-8') as f:
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lines = linehistory(f)
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for line in lines:
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for lineno, hline in lines.history:
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print('{}:{}'.format(lineno, hline), end='')
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for lineno, line in lines:
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print(lineno, ': ', line, end='')
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# for lineno, hline in lines.history:
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# print('{}:{}'.format(lineno, hline), end='')
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f = open('demo.py')
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f = open('demo.py', encoding='utf-8')
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lines = linehistory(f)
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t = iter(lines)
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print(next(t))

‎04-generator-and-iterator/iterator_visit.py‎

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# 跳过可迭代对象的开始部分
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with open('/etc/passwd') as f:
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# 去掉文件头部的行
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for line in dropwhile(lambda line: not line.startswith('#'), f):
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# 如下的写法会去掉注释行
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# lines = (line for line in f if not line.startswith('#'))
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print(line, end='')
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# with open('/etc/passwd') as f:
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# # 去掉文件头部的行
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# for line in dropwhile(lambda line: not line.startswith('#'), f):
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# # 如下的写法会去掉注释行
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# # lines = (line for line in f if not line.startswith('#'))
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# print(line, end='')
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# 跳过指定位置的元素
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items = ['a', 'b', 'c', 1, 4, 10, 15]
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items = ['a', 'b', 'c', 1, 2, 4, 10, 15]
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# [3:] 和 [:3]
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for x in islice(items, 3, None):
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print(x)
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# 全部的排列组合
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for p in permutations(items):
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print(p)
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print(p,)
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print('--------')
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# 指定数量的排列组合
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for p in permutations(items, 2):
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print(p)
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print('--------')
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# 去除元素相同的排列组合(不考虑顺序)
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for i in combinations(items, 2):
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print(i)
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print('--------')
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# 元素被选取就会从候选中剔除掉, 就不会再考虑它
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for c in combinations_with_replacement(items, 3):
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print(c)
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print('--------')
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# 负责的迭代可以参考 itertools
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items = [1, 2, [3, 4, [5, 6], 7], 8]
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# Produces 1 2 3 4 5 6 7 8
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for x in flatten(items):
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print(x)
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# sep=':' 不行,只有一个输出
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print(x, end=', ')
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items = ['Dave', 'Paula', ['Thomas', 'Lewis']]
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for x in flatten(items):
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print(x)

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