format spec %b is documented but does not work

[Skaperen]

the format spec %b is documented but does not work:

Output:
lt1/forums /home/forums 1> py2
Python 2.7.12 (default, Nov 19 2016, 06:48:10) 
[GCC 5.4.0 20160609] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> '%x'%15
'f'
>>> '%o'%15
'17'
>>> '%b'%15
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: unsupported format character 'b' (0x62) at index 1
>>> 
lt1/forums /home/forums 2> py3
Python 3.5.2 (default, Nov 17 2016, 17:05:23) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> '%x'%15
'f'
>>> '%o'%15
'17'
>>> '%b'%15
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: unsupported format character 'b' (0x62) at index 1
>>> 
lt1/forums /home/forums 3>