python学习——推导式

推导式

• 用一句话来生成一个列表
• 语法：[结果 for循环  条件判断]
1. 列表推导式：[结果 for循环 条件筛选]（鸡）
2. 字典推导式：{k:v for循环 条件筛选}
3. 集合推导式：{k for循环 条件}

列表推导式

lst = ['python'+str(i) for i in range(6) if i%2==1]

print(lst)

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['python1', 'python3', 'python5']

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#找到名字里有两个e的名字 names = [['Tom','Billy','Jefferson','Andrew'],['Alice','Jill','Jennifer']] lst = [name for line in names for name in line if name.count('e')==2]  print(lst) ---------------------- ['Jefferson', 'Jennifer'] ====================================

字典推导式

将[11,22,33,44]转换成{0:11,1:22,2:,3:44}

lst = [11,22,33,44]

dic = {i:lst[i] for i in range(len(lst)) if i < 2}

print(dic)

---------------------------

{0: 11, 1: 22}

====================

键值对换

dic = {'jj':'林俊杰','jay':'周杰伦'}

new_dic = {v:k for k,v in dic.items()}

print(new_dic)

-----------------------------------

 {'林俊杰': 'jj', '周杰伦': 'jay'}

======================

集合推导式

去重操作

lst = [1,1,2,2,5,4,2,5,7,9]

s = {i for i in lst}

print(s)

 ----------------------------------------

 {1, 2, 4, 5, 7, 9}

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