pad binary string with a given byte value (python 3)
Peter Otten
__peter__ at web.de
Sat Sep 20 08:05:43 EDT 2014
Nagy László Zsolt wrote:
> >>> BS = 16
> >>> pad = lambda s: s + (BS - len(s) % BS) * chr(BS - len(s) % BS)
> >>> pad('L')
> 'L\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f\x0f'
> >>> pad(b'L')
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> File "<stdin>", line 1, in <lambda>
> TypeError: can't concat bytes to str
>
> How do I write this function so it can pad byte strings? chr(charcode)
> creates a normal string, not a binary string.
>
> I can figure out way for example this:
>
> >>> b'T'+bytearray([32])
>
> but it just don't seem right to create a list, then convert it to a byte
> array and then convert it to a binary string. What am I missing?
bytes/str.ljust()
>>> def pad(b, n=16, c=b"\x0f"):
... length = (len(b)+n-1)//n*n
... return b.ljust(length, c)
...
>>> pad(b"abc", 5)
b'abc\x0f\x0f'
>>> pad(b"abcde", 5)
b'abcde'
>>> pad(b"abcdef", 5)
b'abcdef\x0f\x0f\x0f\x0f'
>>> pad("abcde", 5, "*")
'abcde'
>>> pad("abcdef", 5, "*")
'abcdef****'
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