Dennis Sweeney <[email protected]> added the comment:
If I understand correctly, this shows the behavior you're objecting to:
>>> class A:
... def __getitem__(self, key):
... print(f"{key = }")
... return "apple"
...
...
>>> '{0[1]}'.format(A()) # passes an integer
key = 1
'apple'
>>> '{0[apple]}'.format(A()) # passes a string
key = 'apple'
'apple'
>>> '{0["1"]}'.format(A()) # passes the length-3 string including double-quotes
key = '"1"'
'apple'
There's no clear way to use str.format() to get the value for the string key
"1". However, I don't think it makes sense to backwards-incompatibly change the
behavior to pass the string "1" instead of the integer 1, since a common use is
indexing with integers like
>>> "{0[0]}{0[2]}{0[4]}".format(("a", "b", "c, "d", "e"))
'ace'
This is an edge case, but it is aligned with the specification: according to
https://docs.python.org/3/library/string.html#format-string-syntax,
"""Because arg_name is not quote-delimited, it is not possible to specify
arbitrary dictionary keys (e.g., the strings '10' or ':-]') within a format
string."""
----------
nosy: +Dennis Sweeney
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<https://bugs.python.org/issue44683>
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