标签：space fun file top 基础 range cond 2-2 构造
1 列表推导式定义
列表推导式能非常简洁的构造一个新列表:只用一条简洁的表达式即可对得到的元素进行转换变形
2 列表推导式语法
基本格式如下：
[expr for value in collection if condition]
过滤条件可有可无，取决于实际应用，只留下表达式
列表推导式例子：
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l=["egg%s"%i for i in range(10)]print(l) |
类似于这段for代码：
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egg_list=[]for i in range(10): egg_list.append("egg%s"%i)print(egg_list) |
列表推导式还可以加更多的if判断for循环
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l=[‘egg%s‘ %i for i in range(1,101)]l=[‘egg%s‘ %i for i in range(1,101) if i >50 ]l=[‘egg%s‘ %i for i in range(1,101) if i >50 if i<60]print(l) |
3 列表推导式优点
方便，改变了编程习惯，属于声明式编程
举例：
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l=[1,2,3,4]s="hello"l1=[(num,i) for num in l for i in s]print(l1) |
输出结果为：
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[(1, ‘h‘), (1, ‘e‘), (1, ‘l‘), (1, ‘l‘), (1, ‘o‘), (2, ‘h‘), (2, ‘e‘), (2, ‘l‘), (2, ‘l‘), <br>(2, ‘o‘), (3, ‘h‘), (3, ‘e‘), (3, ‘l‘), (3, ‘l‘), (3, ‘o‘), (4, ‘h‘), (4, ‘e‘), (4, ‘l‘), <br>(4, ‘l‘), (4, ‘o‘)] |
这个列表推导式相当于：
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l=[1,2,3,4]s="hello"l1=[]for num in l: for i in s: t=(num,i) l1.append(t)print(l1) |
4 列表表达式例子
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import osg=os.walk("C:\python_fullstack_wen\day24\wen")file_path_list=[]for i in g: for j in i[-1]: file_path_list.append("%s\\%s"%(i[0],j))print(file_path_list)g=os.walk("C:\python_fullstack_wen\day24\wen")file_path_list=["%s\\%s"%(i[0],j) for i in g for j in i[-1]]print(file_path_list) |
输出结果：
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[‘C:\\python_fullstack_wen\\day24\\wen\\yan1.txt‘, ‘C:\\python_fullstack_wen\\day24\\wen\\wen1<br>\\yan1.txt‘, ‘C:\\python_fullstack_wen\\day24\\wen\\wen1\\jie1\\yan1.txt‘, <br>‘C:\\python_fullstack_wen\\day24\\wen\\wen1\\yan1\\yan1.txt‘, <br>‘C:\\python_fullstack_wen\\day24\\wen\\wen2\\yan2.txt‘][‘C:\\python_fullstack_wen\\day24\\wen\\yan1.txt‘, ‘C:\\python_fullstack_wen\\day24\\wen\\wen1\\yan1.txt‘, ‘C:\\python_fullstack_wen\\day24\\wen\\wen1\\jie1\\yan1.txt‘, ‘C:\\python_fullstack_wen\\day24\\wen\\wen1\\yan1\\yan1.txt‘, ‘C:\\python_fullstack_wen\\day24\\wen\\wen2\\yan2.txt‘] |
