Python list comprehension, generator expressions, dictionary derivation, derivation using collections

Python list comprehension, generator expressions, dictionary derivation, derivation using collections

推导式是可以从一个数据序列构建另一个新的数据序列的结构体

First, list comprehensions:

Use []parentheses generate a list

General operation:

# 需求：将my_list列表中的奇数取出, 并且将取出的奇数相乘, 并且返回
my_list = [1, 2, 3, 4, 5, 6, 7, 8]
new_list = []
for item in my_list:
    if item % 2 == 1:
        new_list.append(item*item)
print(new_list)

# 输出结果如下：[1, 9, 25, 49]

Operation list derived using the formula:

my_list = [1, 2, 3, 4, 5, 6, 7, 8]
new_list = [item * item for item in my_list if item % 2 == 1]
print(new_list)

# 输出结果：[1, 9, 25, 49]

Second, the generator expression:

Use ()parentheses generator into the derivation of formula list []changed ()can be obtained Builder

my_list = [1, 2, 3, 4, 5, 6, 7, 8]
new_genertor = (item for item in my_list if item % 2 == 1)

print(new_genertor)  # 输出结果：<generator object <genexpr> at 0x0000027752962200>

# 循环生成器
for item in new_genertor:
    print(item)
# 输出结果如下：
1
3
5
7

Third, dictionary comprehensions:

Use {}brackets and the list is stored 键值对, it is a dictionary comprehension

my_dict = {"name": "fe_cow", "age": 22, "sex": "男"}
new_dict = {value: key for key, value in my_dict.items()}

print(type(new_dict))
# 输出结果：<class 'dict'>  可以看出是一个字典

print(new_dict)
# 输出结果：{'fe_cow': 'name', '男': 'sex', 22: 'age'}   仅是将字典中的键值掉换了位置

Fourth, the set of derivation:

Use the same set of derivation is {}bracketed to indicate, with the only difference is that the dictionary derivation, it inside不是键值对

my_dict = {"name": "fe_cow", "age": 22, "sex": "男"}
new_set = {key for key, value in my_dict.items()}

print(type(new_set))
# 输出结果：<class 'set'>   可以看出它是一个集合类型

print(new_set)
# 输出结果：{'sex', 'name', 'age'}

These are some simple derivation use is not recommended to use more complex logic for processing derivations, 因为代码的可读性是很重要的.