python文件读取 readlines

     1.txt
1
2
3
1

     2.txt
A
B
C
D

#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())

1A
1B
1C
1D

#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()))

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

#可用写法1
f1=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())

#可用写法2
with 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())