New submission from Iago-lito - <iago.bonn...@gmail.com>:
Consistent with [PEP 3131](https://www.python.org/dev/peps/pep-3131/) and NFKC
normalization of identifiers, these two last lines yield an error, since `𝜏`
(U+1D70F) is automatically converted to `τ` (U+03C4).
class Base(object):
def __init__(self):
self.𝜏 = 5 # defined with U+1D70F
a = Base()
print(a.𝜏) # 5 # (U+1D70F) expected and intuitive
print(a.τ) # 5 as well # (U+03C4) normalized version, okay.
d = a.__dict__ # {'τ': 5} # (U+03C4) still normalized version
print(d['τ']) # 5 # (U+03C4) consistent with normalization
assert hasattr(a, 'τ') # (U+03C4) consistent with normalization
# But if I want to retrieve it the way I entered it because I can type
(U+1D70F)
print(d['𝜏']) # KeyError: '𝜏' # (U+1D70F) counterintuitive
assert hasattr(a, '𝜏') # Fails # (U+1D70F) counterintuitive
I've described and undestood the problem in [this
post](https://stackoverflow.com/questions/48063082/).
Nothing is unconsistent here. However, I am worried that:
- this behaviour might be counterintuitive and misleading, especially if it
occurs that the character user can easily enter for some reason (e.g. U+1D70F)
is not equivalent to its NFKC normalization (e.g. U+03C4)
- this behaviours makes it more difficult to enjoy python's reflective
`__dict__`, `hasattr` and `getattr` features in this particular case.
Maybe it is user's responsibility to be aware of this limitation, and to keep
considering utf-8 coding a bad practice. In this case, maybe this particular
reflective limitation could be made explicit in PEP 3131.
Or maybe it is python's responsibility to ensure intuitive and consistent
behaviour even in tricky-unicode-cases. So reflective features like
`__dict__.__getitem__`, `hasattr` or `getattr` would NFKC-convert their
arguments before searching just like `a.𝜏` does, so that:
getattr(a, '𝜏') is gettatr(a, 'τ')
always yields True.
I actually have no idea of the philosophy to stick to. And the only purpose of
this post is to inform the community about this particular, low-priority case.
Thank you for supporting Python anyway, cheers for your patience.. and happy
2018 to everyone :)
--
Iago-lito
----------
components: Unicode
messages: 309382
nosy: Iago-lito -, ezio.melotti, vstinner
priority: normal
severity: normal
status: open
title: Misleading reflective behaviour due to PEP 3131 NFKC identifiers
normalization.
type: behavior
versions: Python 3.5
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue32483>
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