Raymond Hettinger added the comment:
The use of a bare identifier as a self-assigning statement is unprecedented in
the world of Python. PyFlakes flags it as an error (because prior to now, a
bare identifier in a class statement was almost always an error). I suspect
this will cause issues with other static analysis and refactoring tools as well:
--- tmp_enum_example.py -----
from enum import AutoEnum
class Color(AutoEnum):
red
green = 5
blue
print(list(Color))
--- bash session ------------
$ py -m pyflakes tmp_enum_example.py
tmp_enum_example.py:4: undefined name 'red'
tmp_enum_example.py:6: undefined name 'blue'
tmp_enum_example.py:11: undefined name 'yellow'
Also, the usual technique of commenting out blocks with triple quotes
introduces unexpected breakage:
--- tmp_enum_example2.py -----
from enum import AutoEnum
class Color(AutoEnum):
red
green = 5
blue
''' XXX temporarily comment these out
brown
orange
'''
yellow
print(list(Color))
--- bash session ------------
$ py -m tmp_enum_example.py
[<Color.red: 1>, <Color.green: 5>, <Color.blue: 6>, <Color.yellow: 7>]
/Users/raymond/cpython/python.exe: Error while finding spec for
'tmp_enum_example.py' (AttributeError: module 'tmp_enum_example'
has no attribute '__path__')
I worry that this proposal is worse than just being non-idiomatic Python. In a
way, it undermines pillars of the language and conflict everyone's mental model
of how the language works. Historically, a bare variable name raised a
NameError if undefined and would otherwise act as a expression who's result was
discarded. However, as used here, it fiats an attribute into existence and
assigns it a value. That to my eyes looks like a new language that isn't
Python. This is really weird and undermines my expectations.
The need for the "ignore" parameter for the "shielded set" is a hint that the
patch is working against the grain of the language and is not in harmony with
Python as a coherent whole. It is a harbinger of problems to come.
Lastly, I question whether there is any real problem being solved. You already
have "Color = IntEnum('Animal', 'red green blue')" that works well enough,
doesn't mess with language norms, that works nicely with triple quotes for
multiline entries, and that extends easily to hundreds of constants.
It seems to me that too much magic and unidiomatic weirdness are being leveled
at too small of a problem. Plus we already have one way to do it.
In teaching people to make effective use of the language, a key learning point
is learning the portents of trouble to come and recognizing that that not
everything that can be made to work should actually be done.
Please reconsider whether you really want to open this Pandora's box. Right
now, it's not too late. No doubt that you will find some people who like this
(it reminds them of C), but you will also find some very experienced developers
who are made queasy by the bare identifier transforming from an expression into
an assigning statement. This more than an "if you don't like it, don't use it"
decision, I think an important and invisible line is being crossed that we will
regret.
P.S. A lesson I learned from maintaining the itertools module is that adding
more variants of a single idea tends to make the overall toolkit harder to
learn and impairs usability. Users suffer when given too many choices for
closely related tasks. The "one way to do it" line in the Zen of Python is
there for a reason.
----------
nosy: +rhettinger
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<http://bugs.python.org/issue26988>
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