Why does Python remove the last character of a string?

Question

For example, if I do this str(bin(66)) I get 0b1000010 , but if I do this str(bin(66)).strip("0b") , I get 100001 (notice the missing '0').

I think I'm misusing the strip function.

Answer 1

strip strips characters from both sides. Use lstrip to only strip characters from the left-hand side.

In [27]: str(bin(66)).strip("0b")
Out[27]: '100001'

In [28]: str(bin(66)).lstrip("0b")
Out[28]: '1000010'

Alternatively, just use the format method:

In [38]: '{:b}'.format(66)
Out[38]: '1000010'

Answer 2

From docs :

str.strip([chars])

Return a copy of the string with the leading and trailing characters removed. The chars argument is a string specifying the set of characters to be removed. If omitted or None, the chars argument defaults to removing whitespace. The chars argument is not a prefix or suffix ; rather, all combinations of its values are stripped

So, you're thinking that str.strip will remove the prefix "0b" , but it doesn't work that way. It simply considers '0' and 'b' as two different characters and removes them from the start and end of the string. Same thing applies to both str.rstrip and str.lstrip they don't remove prefix or suffix, but combination of individual characters.

For example:

>>> "0b00101".lstrip("0b")  #just an example case, removes more than just "0b"
'101'

Another example:

>>> strs = "foofoofoobarfoo"
>>> strs.lstrip('fo')
'barfoo'

>>> if strs.startswith('fo'):          #this works fine
       print strs.replace('fo','',1)
...     
ofoofoobarfoo

For binary numbers apart from solutions suggested by @unutbu, you can also try slicing :

>>> str(bin(66))[2:]
'1000010'

or format :

>>> format(66, 'b')
'1000010'