字符串连接与列表中的空字符串

Question

Short context: I have a Python application that has a long string with mixed line endings: \n and \r\n . I'm trying to convert the line endings to Windows line endings \r\n with the following code:

s = "one\r\ntwo\r\n\r\nthree\n\nfour\nfive\r\n\r\n"
lines = s.splitlines()
print(lines)
out = '\r\n'.join(lines)
print(repr(out))
print(out, end='')

The output is:

['one', 'two', '', 'three', '', 'four', 'five', '']
'one\r\ntwo\r\n\r\nthree\r\n\r\nfour\r\nfive\r\n'
one
two

three

four
five

The only caveat is that last empty string, I'd like it to generate an empty line for it, like the other empty lines in the input (like the one between 'two' and 'three').

It's curious that if I change my input string to

s = "one\r\ntwo\r\n\r\nthree\n\nfour\nfive\r\n\r\n\r\n"

The output is:

['one', 'two', '', 'three', '', 'four', 'five', '', '']
'one\r\ntwo\r\n\r\nthree\r\n\r\nfour\r\nfive\r\n\r\n'
one
two

three

four
five

So the problem is that join() seems to be inconsistent by skipping that last empty string.

Long context: This application reads some XML files with LXML, and those files have the Unix termination \n . I do some processing with them that creates strings that have the Windows termination. So then they're put together, I get this string with mixed termination.

Answer 1

You might use a pattern to match an optional \r followed by \n and use \r\n in the replacement.

import re
s = "one\r\ntwo\r\n\r\nthree\n\nfour\nfive\r\n\r\n"
s = re.sub(r"\r?\n", r"\r\n", s)
print(s)

one
two

three

four
five