"this line break must stay.
but this one
not."

"this line break must stay.
but this one not."

import re
p = re.compile('(?<!(?|!|.))n', re.MULTILINE)
text = "hello,nMy name is Hal.nHow arenyou doing?n"
re.sub(p, ' ', text)
# outputs:
'hello, My name is Hal.nHow are you doing?n'