Bugs item #1276587, was opened at 2005-08-30 14:52
Message generated for change (Comment added) made by birkenfeld
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Category: Python Interpreter Core
Group: Python 2.4
>Status: Closed
>Resolution: Wont Fix
Priority: 5
Submitted By: Mike Foord (mjfoord)
Assigned to: Nobody/Anonymous (nobody)
Summary: dict('') doesn't raise a value error
Initial Comment:
The dict function will theoretically accept any sequence
or bounded iterable that yields (key, value) tuples.
A side effect is that dict('') is valid - producing an emtpy
dictionary.
dict(x) where x is *any* string other than '' fails with a
ValueError. I suggest that dict('') ought to produce a
ValueError to as a string is *never* a valid input to the
dict function.
The current situation allows obscure errors to pass
unnoticed.
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>Comment By: Reinhold Birkenfeld (birkenfeld)
Date: 2005-09-01 00:17
Message:
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Closing as Won't Fix, then.
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Comment By: Tim Peters (tim_one)
Date: 2005-08-30 16:39
Message:
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It's not theoretical: it's a fact that dict() accepts any iterable
producing iterables each producing 2 objects (the latter don't
have to be tuples; a (key, value) tuple is just one kind of
iterable producing 2 objects; e.g., dict(["ab"]) == {'a': 'b'}).
An empty str meets the input requirements, so there's no
way to stop this without special-case type-sniffing. That's
very unattractive, in part because it's impossible to guess
which kinds of empty iterables would necessarily lead to an
exception when passed to dict() had they not been empty.
For example, passing an empty array.array (of any flavor) to
dict() also constructs an empty dict. The universe of iterable
objects is vast.
Keeping it uniform and easy to explain (an empty iterable
produces an empty dict) seems better to me than adding a
maze of special cases that's bound to change over time
("except for an empty str" ... "oh, or an empty
unicode" ... "oh, or an empty array.array" ... "oh, or an empty
file" ... "oh, oops, guess not, cuz a file with two lines works
fine" ... etc).
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