I have some code that I have been porting from 2.7 to 3.6/3.7. Most of the unit tests, which have a pretty good coverage, already execute successfully under 3.x. But I have yet to fully commit to switching over to 3.x for development.
I recently noticed, when running black - the code formatter that it chokes if my code would not compile under 3.x, with a message about 3.6 AST-based parsing failing.
Is black a reliable indicator of 3.x-readiness, at least at the syntax level? I know that 2to3 is the tool to use. And I know that for example, it would not catch differences in the standard library (basestring disappearing, StringIO.StringIO becoming io.StringIO, etc...).
but it seems nice that a code formatter could incidentally help out as well.
very basic sample, invalid syntax for 3.x:
print "a", 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21
gives:
error: cannot format test_black.py:
cannot use --safe with this file; failed to parse source file with
Python 3.6's builtin AST.
Re-run with --fast or stop using deprecated Python 2 syntax.
AST error message: Missing parentheses in call to 'print'.
Did you mean print("a", 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)? (<unknown>, line 1)
All done!
1 file failed to reformat.
fix the syntax to 3.x and it works.
If I do the right thing, and add parenthesis print ("a", 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21), then all's well:
reformatted test_black.py
All done! ✨ ✨
1 file reformatted.
