Python list derivation

1 List-derived definitions

The list derivation can be very concise to construct a new list: The resulting element can be transformed with a simple expression

2 List derivation syntax

The basic format is as follows:

[Expr for value in collection if condition]

Filter conditions are optional, depending on the actual application, leaving only the expression

Example of a list derivation:

12	l=["egg%s"%i fori inrange(10)]print(l)

Similar to this for code:

1234	egg_list=[]fori inrange(10):    egg_list.append("egg%s"%i)print(egg_list)

　　

The list derivation can also add more if to judge the For loop

1234	l=[‘egg%s‘%i fori inrange(1,101)]l=[‘egg%s‘%i fori inrange(1,101) ifi >50]l=[‘egg%s‘%i fori inrange(1,101) ifi >50 ifi<60]print(l)

　

3 List Derivation Benefits

Convenient, change the programming habit, belong to the declarative programming

Example:

1234	l=[1,2,3,4]s="hello"l1=[(num,i) fornum inl fori ins]print(l1)

The output is:

1	[(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‘)]

　　

This list derivation is equivalent to:

12345678

l=[1,2,3,4]s="hello"l1=[]fornum inl:    fori ins:        t=(num,i)        l1.append(t)print(l1)

4 Examples of list expressions

1234567891011

importosg=os.walk("C:\python_fullstack_wen\day24\wen")file_path_list=[]fori ing:    forj ini[-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) fori ing forj ini[-1]]print(file_path_list)

Output Result:

12

[‘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‘]

Python list derivation