列表推倒式

Posted 2021-02-20 jnsn

列表推倒式

# 循环模式：[变量(加工的变量) for 变量 in iterable]
# 筛选模式: [变量(加工的变量) for 变量 in iterable if 条件]
# 多层嵌套
l = [x for x in range(1, 11, 2)]
print(l)  # [1, 3, 5, 7, 9]

l = [x**2 for x in range(10)]
print(l)  # [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

# [‘python0期‘, ‘python1期‘, ‘python2期‘, ‘python3期‘, ‘python4期‘]
l = [f‘python{x}期‘ for x in range(5)]
print(l)

l = [i for i in range(30) if i % 3 ==0]
print(l)  # [0, 3, 6, 9, 12, 15, 18, 21, 24, 27]


l = [‘hello‘, ‘hi‘, ‘wonderful‘]
l1 = [x.upper() for x in l if len(x) > 3]
print(l1)  # [‘HELLO‘, ‘WONDERFUL‘]

# 多重循环
names = [[‘Tom‘, ‘Billy‘, ‘Jefferson‘, ‘Andrew‘, ‘Wesley‘, ‘Steven‘, ‘Joe‘],
         [‘Alice‘, ‘Jill‘, ‘Ana‘, ‘Wendy‘, ‘Jennifer‘, ‘Sherry‘, ‘Eva‘]]

# 普通方式
l1 = []
for i in names:
    for j in i:
        if j.count(‘e‘) >= 2:
            l1.append(j.upper())
print(l1)

#  列表推倒式方式
name = [j.upper() for x in names for j in x if j.count(‘e‘) >= 2]
print(name)


# 生成器表达式也包括循环模式。筛选模式， 嵌套等 。
# 列表推倒式[]  生成器表达式()
# 列表推倒式是 iterable ;  生成器表达式是iterator

l = (x for x in range(3))
print(type(l))  # <class ‘generator‘>
# print(next(l)) # 0
# print(next(l)) # 1
for i in l:
    print(i)  # 0 1 2


# 字典推倒式

name = [‘路飞‘, ‘娜美‘, ‘罗宾‘]
hobby = [‘肉‘, ‘钱‘, ‘考古‘]
# 方式1
dic = {}
for i in range(len(name)):
    dic[name[i]] = hobby[i]
print(dic)  # {‘路飞‘: ‘肉‘, ‘娜美‘: ‘钱‘, ‘罗宾‘: ‘考古‘}

# 方式2
dic = {name[i]: hobby[i] for i in range(len(name))}
print(dic)  # {‘路飞‘: ‘肉‘, ‘娜美‘: ‘钱‘, ‘罗宾‘: ‘考古‘}


# 集合推倒式
print({x for x in range(3)})  # {0, 1, 2}