（期末考试卷一卷）python列表推导式详解

• 普通的推导式

list_b = [b for b in range(5)]
print(list_b)
# 与下面的代码等价：
list_a = list()
for a in range(5):
    list_a.append(a)
print(list_a)

[0, 1, 2, 3, 4]
[0, 1, 2, 3, 4]

-那什么是生成器表达式呢？

print(b for b in range(5)) # b for b in range(5)就是生成器表达式

 at 0x000001A78BF8AA50>

-可以通过list（）函数将生成器转换为列表

print(list(b for b in range(5)))

[0, 1, 2, 3, 4]

• 带if判断的推导式

list_d = [d for d in range(6) if d % 2 != 0]
print(list_d)
# 与下面的代码等价：
list_d=list()
for d in range(6):
    if d%2!=0:
        list_d.append(d)
print(list_d)

[1, 3, 5]
[1, 3, 5]

• 两个for循环的推导式

list_e = [(e, f * f) for e in range(3) for f in range(5, 15, 5)]
print(list_e)
# 与下面的代码等价：
list=[]
for e in range(3):
    for f in range(5,15,5):
        list.append((e,f**2))
print(list)

[(0, 25), (0, 100), (1, 25), (1, 100), (2, 25), (2, 100)]
[(0, 25), (0, 100), (1, 25), (1, 100), (2, 25), (2, 100)]

• 嵌套加判断的推导式

list_g = [[x for x in range(g - 3, g)] for g in range(22) if g % 3 == 0 and g != 0]
print(list_g)
# 与下面的代码等价：
list1=[]
for g in range(22):
    if g % 3 == 0 and g != 0:
        list1.append([x for x in range(g - 3, g)])
print(list1)

[[0, 1, 2], [3, 4, 5], [6, 7, 8], [9, 10, 11], [12, 13, 14], [15, 16, 17], [18, 19, 20]]
[[0, 1, 2], [3, 4, 5], [6, 7, 8], [9, 10, 11], [12, 13, 14], [15, 16, 17], [18, 19, 20]]

• （推广）字典的基本推导式

dict_a = {key: value for key in 'python' for value in range(2)}
print(dict_a)
# 对同一个key值多次赋予value值，取最后赋予的值
l={}
for key in 'python':
    for value in range(2):
        l[key]=value
print(l)

{'p': 1, 'y': 1, 't': 1, 'h': 1, 'o': 1, 'n': 1}
{'p': 1, 'y': 1, 't': 1, 'h': 1, 'o': 1, 'n': 1}