5个小问题带你理解列表推导式

问题1 用列表表示集合X

直接敲出来

X = [1,2,3,4,5,6,7,8,9,10]
X

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

也可以

X = list(range(1, 11))
X

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

问题2 表示集合B

B = []
for x in X:
    B.append(x*x) 
B

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

列表推导式

列表推导式代码简洁，可读性强。

[x*x for x in X]

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

如何理解列表推导式

实现步骤

先复制X

#复制X本身
[x for x in X]

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

#对X中的每一个元素进行操作
[x*x for x in X]

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

理解，类比上面的集合公式

• x*x 相当于
• for 相当于 |
• in 相当于

带条件的列表推导式

C = [x*x for x in range(1, 11) if x%2==1]
C

[1, 9, 25, 49, 81]

#断行
C = [a*a 
     for a in range(1, 11) 
     if a%2==1]
C

[1, 9, 25, 49, 81]

问题3 全部小写

words = ['Life', 'is', 'short', 'so', 'we', 'use', 'Python', 'python', 'is', 'easy', 'to', 'learn', 'and', 'easy', 'to', 'use']
words

['Life',
 'is',
 'short',
 'so',
 'we',
 'use',
 'Python',
 'python',
 'is',
 'easy',
 'to',
 'learn',
 'and',
 'easy',
 'to',
 'use']

lower_words = [w.lower() for w in words]
lower_words

['life',
 'is',
 'short',
 'so',
 'we',
 'use',
 'python',
 'python',
 'is',
 'easy',
 'to',
 'learn',
 'and',
 'easy',
 'to',
 'use']

问题4 计算lower_words列表数据的单词词频

wordset = set(lower_words)
wordset

{'and',
 'easy',
 'is',
 'learn',
 'life',
 'python',
 'short',
 'so',
 'to',
 'use',
 'we'}

[(w, lower_words.count(w))
 for w in wordset]

[('we', 1),
 ('learn', 1),
 ('to', 2),
 ('so', 1),
 ('python', 2),
 ('is', 2),
 ('and', 1),
 ('use', 2),
 ('easy', 2),
 ('short', 1),
 ('life', 1)]

问题5

d = {'x': 'A', 
     'y': 'B', 
     'z': 'C' }

如何将d中的 键值对 拼接,输出为

['xA', 'yB', 'zC]

d = {'x': 'A', 
     'y': 'B', 
     'z': 'C' }

d.items()

dict_items([('x', 'A'), ('y', 'B'), ('z', 'C')])

[item for item in d.items()]

[('x', 'A'), ('y', 'B'), ('z', 'C')]

[item[0]+item[1] for item in d.items()]

['xA', 'yB', 'zC']

精彩回顾

万水千山总是情，给我点好看可好❤