如何从最后一个“。”之后的字符串中删除最后一个字符

Question

Im working on a python scipt which gets and Ip and calculates the brodcast which just removes the last digest of the ip after the last "." and replaces them with 255

input = "192.168.0.100" 
input = #string operation
print(input)

Answer 1

input = "192.168.0.100" 
loc = input.rfind('.')
inputShort = input[1:loc]
print(loc)
print(inputShort)

rfind finds the last incidence of the "." character and inputShort is then all characters up until, but excluding the last ".".

Answer 2

Broadcast address is not always going to be just 255 as last digest. That would be true only if the prefix len is /24 (or mask is 255.255.255.0).

Answer 3

>>> input = "192.168.0.100"
>>> from re import sub
>>> sub('(.[01]?[0-9]?[0-9]|2[0-4][0-9]|25[0-4])$', '.255', input)
'192.168.5.255'