Python 教程之控制流（12）组合迭代器

组合迭代器

用于简化组合构造（如排列、组合和笛卡尔积）的递归生成器称为组合迭代器。
在Python中，有4个组合迭代器：

• 产品（）：此工具计算输入可迭代对象的笛卡尔积。为了计算可迭代对象与自身的乘积，我们使用可选的 repeat 关键字参数来指定重复次数。此函数的输出是按排序顺序排列的元组。
  例：

# 从 itertools 模块导入产品功能
from itertools import product

print("The cartesian product using repeat:")
print(list(product([1, 2], repeat = 2)))
print()

print("The cartesian product of the containers:")
print(list(product(['geeks', 'for', 'geeks'], '2')))
print()

print("The cartesian product of the containers:")
print(list(product('AB', [3, 4])))

输出：

The cartesian product using repeat:
[(1, 1), (1, 2), (2, 1), (2, 2)]

The cartesian product of the containers:
[('geeks', '2'), ('for', '2'), ('geeks', '2')]

The cartesian product of the containers:
[('A', 3), ('A', 4), ('B', 3), ('B', 4)]

• 排列（）：名称不言自明的排列（）用于生成可迭代的所有可能的排列。所有元素都根据其位置而不是其值被视为唯一元素。此函数采用可迭代且group_size，如果未指定group_size的值或等于 None，则group_size的值将成为可迭代的长度。
  例：

# 从itertools模块导入产品功能
from itertools import permutations

print ("All the permutations of the given list is:")
print (list(permutations([1, 'geeks'], 2)))
print()

print ("All the permutations of the given string is:")
print (list(permutations('AB')))
print()

print ("All the permutations of the given container is:")
print(list(permutations(range(3), 2)))

输出：

All the permutations of the given list is:
[(1, 'geeks'), ('geeks', 1)]

All the permutations of the given string is:
[('A', 'B'), ('B', 'A')]

All the permutations of the given container is:
[(0, 1), (0, 2), (1, 0), (1, 2), (2, 0), (2, 1)]

• 组合（）：此迭代器按排序顺序打印在指定组大小中传入的参数的所有可能组合（不带替换）。
  例：

# 从itertools模块导入组合

from itertools import combinations

print ("All the combination of list in sorted order(without replacement) is:")
print(list(combinations(['A', 2], 2)))
print()

print ("All the combination of string in sorted order(without replacement) is:")
print(list(combinations('AB', 2)))
print()

print ("All the combination of list in sorted order(without replacement) is:")
print(list(combinations(range(2), 1)))

输出：

All the combination of list in sorted order(without replacement) is:
[('A', 2)]

All the combination of string in sorted order(without replacement) is:
[('A', 'B')]

All the combination of list in sorted order(without replacement) is:
[(0, ), (1, )]

• Combinations_with_replacement（）：此函数从可迭代元素返回长度为 n 的子序列，其中 n 是函数确定函数生成的子序列长度的参数。单个元素可能会在combinations_with_replacement功能中重复出现。
  例：

# 从itertools模块导入组合

from itertools import combinations_with_replacement

print ("All the combination of string in sorted order(with replacement) is:")
print(list(combinations_with_replacement("AB", 2)))
print()

print ("All the combination of list in sorted order(with replacement) is:")
print(list(combinations_with_replacement([1, 2], 2)))
print()

print ("All the combination of container in sorted order(with replacement) is:")
print(list(combinations_with_replacement(range(2), 1)))

输出：

All the combination of string in sorted order(with replacement) is:
[('A', 'A'), ('A', 'B'), ('B', 'B')]

All the combination of list in sorted order(with replacement) is:
[(1, 1), (1, 2), (2, 2)]

All the combination of container in sorted order(with replacement) is:
[(0, ), (1, )]