Python file reads the pit of the ReadLines () method

First, demand:

There are two files similar to the following which need to be compared and processed.

     1.txt1231

     2.txtABCD

Second, the question:

The first thing to think about is when you open it, two times for the loop.

#错误写法f1=open(r"D:\pytest\1.txt",‘r‘)f2=open(r"D:\pytest\2.txt",‘r‘)for x in f1.readlines():    for y in f2.readlines():        print(x.strip()+y.strip())

The output results are only

1A1B1C1D

Obviously the first layer has not been looped through.

So the test, look for Ah, finally understand. ReadLines () is a one-time job, read into memory and the iteration is complete without

#输出测试f1=open(r"D:\pytest\1.txt",‘r‘)f2=open(r"D:\pytest\2.txt",‘r‘)x1=f1.readlines()for x in x1:    x2=f2.readlines()    print(‘x2 is : {}‘.format(x2))    for y in x2:        print("X : {}".format(x.strip()))        print("y:{}".format(y.strip()))

Output

x2 is : [‘A\n‘, ‘B\n‘, ‘C\n‘, ‘D‘]   #明显只请求一次X : 1y:AX : 1y:BX : 1y:CX : 1y:Dx2 is : []   #之后不再重新请求，已成空值，外层停止循环x2 is : []x2 is : []

Third, the settlement

You can assign a variable to it in the outer layer to store it . Modify the code as follows, finally 2 layer loop normal output.

#可用写法1f1=open(r"D:\pytest\1.txt",‘r‘)f2=open(r"D:\pytest\2.txt",‘r‘)X1=f1.readlines()X2=f2.readlines()for x in X1:    for y in X2:        print(x.strip()+y.strip())

In the process of finding a method, it is found that the with open is clearer than directly with open and does not use explicit close (), so the code is modified

#可用写法2with open(r"D:\pytest\1.txt",‘r‘) as f1,open(r"D:\pytest\2.txt",‘r‘) as f2:    f11=f1.readlines()    f22=f2.readlines()    for x in f11:        for y in f22:            print(x.strip()+y.strip())

Test environment is under Windows python3.6

Python file reads the pit of the ReadLines () method