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列表推导式唯一的用处就是增强代码的可阅读性,初次接触可能比较难理解,但是大家一定要理解,文本分析中经常会用到ta。



问题1 用列表表示集合X

$X= {x| x \in [1,2,3,4,5,6,7,8,9,10]}$

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

X = list(range(1, 10))
X
[1, 2, 3, 4, 5, 6, 7, 8, 9]



问题2 表示集合Y

$Y = {x^2| x \in [1,2,3,4,5,6,7,8,9,10]}$

Y = []

for x in X:
    Y.append(x*x)
    
Y
[1, 4, 9, 16, 25, 36, 49, 64, 81]



列表推导式

实现步骤

  1. 先复制X
  2. 再对X中的元素x进行操作
#先复制X
[x for x in X]
[1, 2, 3, 4, 5, 6, 7, 8, 9]

#再对x进行操作
[x*x for x in X]
[1, 4, 9, 16, 25, 36, 49, 64, 81]

理解列表推导式


带条件的列表推导式

$C= {x^2 | (x \in X) \cap (x>5)}$

#复制X
[x 
 for x in X]
[1, 2, 3, 4, 5, 6, 7, 8, 9]

#X中的要大于5
#[x for x in X if x>5]


[x 
 for x in X 
 if x>5]


[6, 7, 8, 9]

#对满足条件的x进行操作
#[x*x for x in X if x>5]

[x*x 
 for x in X 
 if x>5]
[36, 49, 64, 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)
[(w, lower_words.count(w)) for w in wordset]
[('so', 1),
 ('and', 1),
 ('learn', 1),
 ('use', 2),
 ('to', 2),
 ('we', 1),
 ('easy', 2),
 ('python', 2),
 ('is', 2),
 ('short', 1),
 ('life', 1)]

#1 生产词语集合
wordset = set(lower_words)
print(wordset)
{'so', 'and', 'learn', 'use', 'to', 'we', 'easy', 'python', 'is', 'short', 'life'}

#2. wordset复制wordset自己
[w for w in wordset]
#3. 对wordset中每个词语w进行一些操作
[lower_words.count(w) for w in wordset]
[1, 1, 1, 2, 2, 1, 2, 2, 2, 1, 1]

#3. 词频和词语一起显示
[(w,lower_words.count(w)) for w in wordset]
[('so', 1),
 ('and', 1),
 ('learn', 1),
 ('use', 2),
 ('to', 2),
 ('we', 1),
 ('easy', 2),
 ('python', 2),
 ('is', 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')])

#1 自己复制d.items()自己
[i for i in d.items()]
[('x', 'A'), ('y', 'B'), ('z', 'C')]

#2 对任何一个元素都要进行字符串的拼接操作
[i[0]+i[1] for i in d.items()]
['xA', 'yB', 'zC']



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