Terry J. Reedy added the comment:
Changing behavior that already matches the docs is an enhancement, not a
bugfix, and one that will almost certainly break code. It is therefore one that
would normally require a deprecation period. I think the most you should ask
for is to skip the deprecation period.
I believe the urllib and difflib problems are quite different. I am going to
presume that urllib simply converts bytes input to str and goes on from there,
returning the result as str rather than (possibly) converting back to bytes.
That is an example for this issue.
Difflib.unified_diff, on the other hand, raises rather than returning an
unexpected or undesired type. The 3 sections like the below have two problems
given the toy input of two bytes objects.
if tag in {'replace', 'delete'}:
for line in a[i1:i2]:
yield '-' + line
First, iterating bytes or a slice of bytes returns ints, not 1-byte bytes.
Hence the exception. Even if that were worked around, the mixed string constant
+ bytes expression would raise a TypeError. One fix for both problems would be
to change the expression to '-' + str(line).
Neither of these problems are bugs. The doc says "Compare a and b (lists of
strings)". Actually, 'sequence of strings' is sufficient. For the operations of
unified_diff, a string looks like a sequence of 1-char strings, which is why
>>> for l in difflib.unified_diff('ab', 'c'): print(l)
---
+++
@@ -1,2 +1 @@
-a
-b
+c
works.
The other lines yielded by unified_diff are produced with str.format, and %
formatting does not seem to work with bytes either. So a dual string/bytes
function would not be completely trivial.
Greg, can you convert bytes to strings, or strings to bytes, for your tests, or
do you have non-ascii codes in your bytes? Otherwise, I think it might be
better to write a new function 'unified_diff_bytes' that did exactly what you
want than to try to make unified_diff accept sequences of bytes.
----------
nosy: +terry.reedy
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<http://bugs.python.org/issue17445>
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