[issue4114] struct returns incorrect 4 byte float

[Martin v. Löwis]

Martin v. Löwis <martin at v.loewis.de> added the comment:

> Don't hesitate to reopen the bug if you consider that
> something should be fixed in Python.

I agree that it should be closed; people should read general CS
introductory material to learn how floating point numbers work.

> @loewis: Yes, the initial problem is about unpack("f", bytes). It's 
> not possible to exact original 32 bits float value

Interestingly enough, it is possible - using the OPs approach.
If you want to truncate a 64-bit floating point number to a
32-bit one, pack it as float in the struct module, then unpack it.
Python will automatically pad the mantissa bytes with null bytes.

> because Python 
> forces a conversion to 64 bits float. The behaviour should be 
> documented. 

I think it's documented somewhere that a Python float is represented
with a C double. That should suffice, IMO.

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<http://bugs.python.org/issue4114>
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