[Python-3000] Immutable bytes type and dbm modules

[Georg Brandl]

Jim Jewett schrieb:
> On 8/7/07, Guido van Rossum <guido at python.org> wrote:
> 
>> If b"..." is immutable, the
>> immutable bytes type is in your face all the time and you'll have to
>> deal with the difference all the time.
> 
> There is a conceptual difference between the main use cases for
> mutable (a buffer) and the main use cases for immutable (a protocol
> constant).
> 
> I'm not sure why you would need a literal for the mutable version.
> How often do you create a new buffer with initial values?  (Note:  not
> pointing to existing memory; creating a new one.)

The same reason that you might create empty lists or dicts: to fill them.

>> E.g. is the result of
>> concatenating a mutable and an immutable bytes object mutable?
>> Does it matter whether the mutable operand is first or second?
> 
> I would say immutable; you're taking a snapshot.  (I would have some
> sympathy for taking the type of the first operand, but then you need
> to worry about + vs +=, and whether the start of the new object will
> notice later state changes.)

But what about

mutable = mutable + immutable

mutable += immutable

I'd expect it to stay mutable in both cases.

Georg

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