[Python-ideas] Python 3.x and bytes

Ethan Furman ethan at stoneleaf.us
Fri May 20 15:05:37 CEST 2011

Terry Reedy wrote:
> As far as I noticed, Ethan did not explain why he was extracting single
> bytes and comparing to a constant, so it is hard to know if he was even
> using them properly.

The header of a .dbf file details the field composition such as name, 
size, type, etc.  The type is C for character, L for logical, etc, and 
the end of the field definition block is signaled by a CR byte.

So in one spot of my code I (used to) have a comparison

if hdr[0] == b'\x0d': # end of fields

which I have changed to

if hdr[0] == 0x0d:

and elsewhere:

field_type = hdr[11]

which is now

field_type = chr(hdr[11])

since the first 127 positions of unicode are ASCII.

However, I can see this silently producing errors for values between 128 
and 255 -- consider:

--> chr(0xa1)
--> b'\xa1'.decode('cp1251')

So because my single element access to the byte string lost its bytes 
type, I may no longer get the correct result.


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