unable to replcae a pattern using method re.sub()

[Jeevananda]

my question here
I am unable to replace a pattern using the method re.sub()

import re

#initialize string

x='<?xml version="1.0" encoding="UTF-8"?><rule stage="Source">'

#extracting a part of string

b=re.findall('(<.+\s.+\?>)',x) ##result will be b=['<?xml version="1.0" encoding="UTF-8"?>']

#now I want to remove the extract part so I am using

print(re.sub(b[0],'',x))

# expected result is <rule stage="Source"> how ever I am getting <?xml version="1.0" encoding="UTF-8"?#><rule stage="Source"> please help