When comparing content with difflib, if the resulting diff covers the
last line of one or both of the inputs that that line doesn't end with
an end-of-line character(s), then the generated diff lines don't include
an EOL. Fair enough.

Naive (and I suspect typical) usage of difflib.unified_diff(...) is:

  diff = ''.join(difflib.unified_diff(...))

This results in an *incorrect* unified diff for the conditions described
above.

>>> from difflib import *
>>> gen = unified_diff("one\ntwo\nthree".splitlines(1),
...                    "one\ntwo\ntrois".splitlines(1))
>>> print ''.join(gen)
---
+++
@@ -1,3 +1,3 @@
 one
 two
-three+trois


The proper behaviour would be:

>>> gen = unified_diff("one\ntwo\nthree".splitlines(1),
...                    "one\ntwo\ntrois".splitlines(1))
>>> print ''.join(gen)
---
+++
@@ -1,3 +1,3 @@
 one
 two
-three
\ No newline at end of file
+trois
\ No newline at end of file


I *believe* that "\ No newline at end of file" are the appropriate
markers -- that tools like "patch" will know how to use. At least this
is what "svn diff" generates.


I'll try to whip up a patch. 

Do others concur that this should be fixed?

Attached is a patch against the Python 2.6 svn trunk for this.

At a glance I suspect this patch will work back to Python 2.3 (when
difflib.unified_diff() was added). I haven't looked at the Py3k tree yet.


Note: This *may* also applied to difflib.context_diff(), but I am not sure.

Here is a new patch that also fixes the same issue in
difflib.context_diff() and adds a couple test cases.