Python - 常用函数 - itertools

曾经终败给现在 2023-10-12 17:16 26阅读 0赞

import itertools
    
    # 1. 生成无限迭代器
    # count函数生成从指定起始值开始的无限整数序列
    counter = itertools.count(start=5, step=2)
    print(next(counter))  # 输出: 5
    print(next(counter))  # 输出: 7
    print(next(counter))  # 输出: 9
    
    # cycle函数无限重复迭代给定的序列
    colors = itertools.cycle(['red', 'green', 'blue'])
    print(next(colors))  # 输出: red
    print(next(colors))  # 输出: green
    print(next(colors))  # 输出: blue
    print(next(colors))  # 输出: red
    print(next(colors))  # 输出: green
    
    # repeat函数重复给定的元素指定的次数
    repeater = itertools.repeat(10, times=3)
    print(next(repeater))  # 输出: 10
    print(next(repeater))  # 输出: 10
    print(next(repeater))  # 输出: 10
    # print(next(repeater))  # 输出: StopIteration
    
    # 2. 组合生成器
    # permutations函数生成指定长度的排列
    perm = itertools.permutations([1, 2, 3], r=2)
    print(list(perm))  # 输出: [(1, 2), (1, 3), (2, 1), (2, 3), (3, 1), (3, 2)]
    
    # combinations函数生成指定长度的组合，相比 permutations 多了去重（无关内部元组的顺序）
    comb = itertools.combinations([1, 2, 3, 4], r=3)
    print(list(comb))  # 输出: [(1, 2, 3), (1, 2, 4), (1, 3, 4), (2, 3, 4)]
    
    # product函数生成多个可迭代对象的笛卡尔积
    prod = itertools.product([1, 2], ['a', 'b'])
    print(list(prod))  # 输出: [(1, 'a'), (1, 'b'), (2, 'a'), (2, 'b')]
    
    # combinations_with_replacement函数生成指定长度的组合，允许元素重复
    comb_wr = itertools.combinations_with_replacement([1, 2, 3], r=2)
    print(list(comb_wr))  # 输出: [(1, 1), (1, 2), (1, 3), (2, 2), (2, 3), (3, 3)]
    
    # 3. 迭代器操作
    # chain函数将多个迭代器链接在一起
    chain = itertools.chain([1, 2, 3], ['a', 'b', 'c'])
    print(list(chain))  # 输出: [1, 2, 3, 'a', 'b', 'c']
    
    # compress函数根据一个选择器迭代器的值筛选元素
    data = [1, 2, 3, 4, 5, 6]
    selector = [True, False, True, False, True, False]
    result = itertools.compress(data, selector)
    print(list(result))  # 输出: [1, 3, 5]
    
    # dropwhile函数从迭代器中丢弃满足特定条件的元素，直到条件第一次为假
    numbers = [1, 3, 5, 2, 4, 6]
    result = itertools.dropwhile(lambda x: x < 5, numbers)
    print(list(result))  # 输出: [5, 2, 4, 6]
    
    # takewhile函数从迭代器中取出满足特定条件的元素，直到条件第一次为假
    result = itertools.takewhile(lambda x: x < 5, numbers)
    print(list(result))  # 输出: [1, 3]
    
    # 4. 其他函数
    # islice函数返回迭代器的切片
    slicer = itertools.islice('ABCDEFG', 2, 5)
    print(''.join(slicer))  # 输出: "CDE"
    
    # tee函数将一个迭代器分为多个独立的迭代器
    iter1, iter2 = itertools.tee([1, 2, 3, 4, 5], 2)
    print(list(iter1))  # 输出: [1, 2, 3, 4, 5]
    print(list(iter2))  # 输出: [1, 2, 3, 4, 5]
    
    # zip_longest函数将多个迭代器对应位置的元素进行配对，以最长的迭代器长度为准
    a = [1, 2, 3]
    b = ['a', 'b']
    zipped = itertools.zip_longest(a, b, fillvalue=None)
    print(list(zipped))  # 输出: [(1, 'a'), (2, 'b'), (3, None)]