使用重复项打开文件错误

Question

我有这样的代码：

​

chain = '>'
contain=''

file = raw_input('Enter your filename : ')


fileName = open(file,'r')
for line in fileName:
	if chain in line :
		pass
			
	if not(chain in line):
		contain+=line
		print contain
		

fileName.close()

​

这个file.txt：

Python supports multiple programming paradigms, including object-oriented, imperative and functional programming. 
It features a dynamic type system and automatic memory management.
He has a large and comprehensive standard library

我得到了“打印”的结果：

Python supports multiple programming paradigms, including object-oriented, imperative and functional programming. 

Python supports multiple programming paradigms, including object-oriented, imperative and functional programming. 
It features a dynamic type system and automatic memory management.

Python supports multiple programming paradigms, including object-oriented, imperative and functional programming. 
It features a dynamic type system and automatic memory management.
He has a large and comprehensive standard library

为什么我有副本？

Answer 1

在循环的每一次迭代中，当：

if not(chain in line):
    contain+=line
    print(contain)

因为您连接了contain中的每一行，所以当您打印它时，它将显示第一个句子，第一个迭代，然后是第二个迭代中的first+second语句，依此类推。因此出现了重复。

将print(contain)替换为print(line)将不重复地打印行。

Answer 2

在第一次迭代之后，将文件的第一行添加到contain中，然后打印出来。

在第二次迭代之后，将文件的第二行添加到contain，其中仍然包含第一行，然后打印它。

第三次迭代也是如此。

您正在看到副本，因为您多次打印contain，并且其中包含前面的行。