[Python-Dev] Re: [spambayes-dev] RE: RE: [Spambayes] Question (orpossibly a bug report)

[Scott David Daniels]

Tim Peters wrote:

>[Scott David Daniels]
>  
>
>>I've been seeing a lot of "we'll have to use float(123)/100"
>>messages floating around, and I'd like to point out there is an
>>atof-able form for floating point numbers:
>>           256.7654e-7  =  2567654e-11
>>    
>>
>
>Skip is right that this won't help.  At compile time, Python doesn't stuff
>pieces of the source code into a .pyc file, it builds the float objects and
>marshals them.  Here's temp.py:
>
>def example():
>    return 1e-1
>
>Then:
>
>  
>
>>>>import temp
>>>>file('temp.pyc', 'rb').read()
>>>>        
>>>>
>';\xf2\r\n\xf1L!?c\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00
>@\x00\x00\x00s\r\x00\x00\x00d\x00\x00\x84\x00\x00Z\x00\x00d\x01
>\x00S(\x02\x00\x00\x00c\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00
>\x00\x00C\x00\x00\x00s\x08\x00\x00\x00d\x01\x00Sd\x00\x00S(\x02
>\x00\x00\x00Nf\x130.10000000000000001(\x00\x00\x00\x00(\x00\x00
>\x00\x00(\x00\x00\x00\x00(\x00\x00\x00\x00s\x07\x00\x00\x00temp.py
>s\x07\x00\x00\x00example\x01\x00\x00\x00s\x02\x00\x00\x00\x00
>\x01N(\x01\x00\x00\x00s\x07\x00\x00\x00example(\x01\x00\x00\x00
>s\x07\x00\x00\x00example(\x00\x00\x00\x00(\x00\x00\x00\x00
>s\x07\x00\x00\x00temp.pys\x01\x00\x00\x00?\x01\x00\x00\x00s\x00
>\x00\x00\x00'
>  
>
>
>The substring
>
>    f\x130.10000000000000001
>
>is the marshal typecode for a float, a byte saying the float string is in
>the next 0x13 = 19 bytes, and then the 19-byte string "0.10000000000000001".
>The source code's exponential notation didn't survive in the .pyc file.
>
>  
>
The idea is to change the unmarshal code to transform the 19-byte string 
to the 24-byte
string '010000000000000001e-17' before calling atof.  I suppose the 
marshal code could be
converted to generate it, but I was suggesting a way of reading the 
current format by fiddling
bytes before calling atof.

-Scott David Daniels