使用\\ r \\ n时，Python额外的行写操作（在VS Code中）

Question

Very new to Python and am following a video tutorial online for learning Python, using VS Code. The following code is being used to generate a text file:

#
# Read and write files using the built-in Python file methods
#

def main():  
  # Open a file for writing and create it if it doesn't exist
  f = open("textfile.txt", "w+")

  # Open the file for appending text to the end


  # write some lines of data to the file
  for i in range(10):
    f.write("This is line " + str(i) + "\r\n")

  # close the file when done
  f.close()


  # Open the file back up and read the contents


if __name__ == "__main__":
  main()

When I run it, I get:

This is line 0

This is line 1

This is line 2

This is line 3

This is line 4

This is line 5

This is line 6

This is line 7

This is line 8

This is line 9

Whereas, the tutor's output is:

This is line 0
This is line 1
This is line 2
This is line 3
This is line 4
This is line 5
This is line 6
This is line 7
This is line 8
This is line 9

I have tried experimenting with the "\\r\\n" and when using either one or the other(as "\\r" or "\\n"), I get the correct response, but with both together it results in the extra line.

I have read somewhere that there is a difference between Windows and Mac for this, but I couldn't find a whole load of details about what these characters are and what they do.

EDIT: I am using Windows, the tutor was using Mac

Answer 1

newline controls how universal newlines works (it only applies to text mode). It can be None, '', '\\n', '\\r', and '\\r\\n'. It works as follows:

On input, if newline is None, universal newlines mode is enabled. Lines in the input can end in '\\n', '\\r', or '\\r\\n', and these are translated into '\\n' before being returned to the caller. If it is '', universal newline mode is enabled, but line endings are returned to the caller untranslated. If it has any of the other legal values, input lines are only terminated by the given string, and the line ending is returned to the caller untranslated.

On output, if newline is None, any '\\n' characters written are translated to the system default line separator, os.linesep. If newline is '', no translation takes place. If newline is any of the other legal values, any '\\n' characters written are translated to the given string.

That means since python 3.2 any newline character (in your case \\r and \\n) is translated to os.linsep which is the line seperator of your os

Source is the python documentation: https://docs.python.org/release/3.2/library/functions.html#open

Answer 2

On Windows, writing \\n is translated to \\r\\n when the file is opened in text mode (the default), so writing \\r\\n gives you \\r\\r\\n. Write \\n only in text mode, which is portable and the correct end of line for the OS is used.

Answer 3

You just need to change the open line to:

f = open("textfile.txt", "w+",newline='')

In case you are using python 2.x then do:

f = open("textfile.txt", "wb+")