23

Do you know any library that will help doing that?

I would write a function that prints the differences between two multiline strings in the unified diff format. Something like that:

def print_differences(string1, string2):
    """
    Prints the comparison of string1 to string2 as unified diff format.
    """
    ???

An usage example is the following:

string1="""
Usage: trash-empty [days]

Purge trashed files.

Options:
  --version   show program's version number and exit
  -h, --help  show this help message and exit
"""

string2="""
Usage: trash-empty [days]

Empty the trash can.

Options:
  --version   show program's version number and exit
  -h, --help  show this help message and exit

Report bugs to http://code.google.com/p/trash-cli/issues
"""

print_differences(string1, string2)

This should print something like that:

--- string1 
+++ string2 
@@ -1,6 +1,6 @@
 Usage: trash-empty [days]

-Purge trashed files.
+Empty the trash can.

 Options:
   --version   show program's version number and exit
Andrea Francia
  • 9,737
  • 16
  • 56
  • 70

2 Answers2

32

This is how I solved:

def _unidiff_output(expected, actual):
    """
    Helper function. Returns a string containing the unified diff of two multiline strings.
    """

    import difflib
    expected=expected.splitlines(1)
    actual=actual.splitlines(1)

    diff=difflib.unified_diff(expected, actual)

    return ''.join(diff)
Andrea Francia
  • 9,737
  • 16
  • 56
  • 70
  • This works except in the case where the the diff is a blank line. `"hello\nthere" != "hello\nthere\n"`. Using `expected = [line for line in expected.split('\n')]` instead will solve this. – Marcel Wilson Mar 29 '19 at 00:29
26

Did you have a look at the built-in python module difflib? Have a look that this example

Nadia Alramli
  • 111,714
  • 37
  • 173
  • 152