regex - How to parse/substitute part of a string given a starting matching condition in python? -

assume have string

text='bla1;\nbla2;\nbla3;\n#endif\nbla4;'

i want define method removes '\n' except if '\n' preceded string starting '#' or '\n' follows '#', result of process should be:

text2='bla1;bla2;bla3;\n#endif\nbla4;'

is there simple way in python using regex?

(note: clear me how avoid \n followed #, using negative lookbehind, i.e. r'\n+(?!#)' challenge how identify \n preceded string starting #)

the challenge is: how deal positive lookbehind variable-length strings in python?

find : (#[a-z]+\\n)|\\n(?!#)

and replace : '\1'

output : bla1;bla2;bla3;\n#endif\nbla4;

this keep \n newline chars have preceding word starting # or followed hash.

hth

GHI