[Tutor] os.urandom()

[Richard D. Moores]

On Sun, Aug 8, 2010 at 01:05, Alan Gauld <alan.gauld at btinternet.com> wrote:
>
> "Richard D. Moores" <rdmoores at gmail.com> wrote
>
>> So if os.urandom() had been written so that it printed only hex,
>> b'l\xbb\xae\xb7\x0ft' would have been
>>
>> b'\x6c\xbb\xae\xb7\x0f\x74' , right?
>
> Yes except that its not urandomthat is printing those values.
> urandom returns a string of bytes.
> Its the Python interpreter calling the repr() function on
> those bytes that is deciding to print either hex or character.
> Try this:
>
>>>> '\x6c\xbb\xae\xb7\x0f\x74'
>
> 'l\xbb\xae\xb7\x0ft'
>>>>
>>>> print '\x6c\xbb\xae\xb7\x0f\x74'
>
> l╗«À☼t
>>>>
>
> In the first case its the repr() of the string that gets
> printed in the second its the str(). Its the conversion
> function that determines what gets printed not urandom()

Ah. Here are some more (from Python 2.6):
>>> s = os.urandom(6);s;print s
'Y\xce\x01\xc6\xd3\xe7'
Y╬☺╞╙τ
>>> s = os.urandom(6);s;print s
'\xd2$\xa1\x03B\xba'
╥$í♥B║
>>> s = os.urandom(6);s;print s
'\xc6\x93C\xca\xc3\x18'
╞ôC╩├↑
>>> s = os.urandom(6);s;print s
'`DTzL\x98'
`DTzLÿ

>> How were we supposed to know that all the hexes have 2 digits? How did
>> you?
>
> Simple arithmetic...
> Its the hex representation of a byte. A byte is 8 bits long.
> A hex digit represents 4 bits (0000-1111) so you need 2 hex digits to
> represent 8 bits or one byte.

Got it. Thanks again. And to Steven as well.

Dick