Sorry for the stupid question.

g = ['mon1-1', 'mon2-2', 'mon3-3']
G2 = ['MON1-1', 'MON2-2']

How to compare G from G2 (two list), if the value does not find, output only what I did not find, and it will be a variable MON3-3.

Answer 1, Authority 100%

If the speed is not critical, then it is possible:

for e in g:
  IF NOT E IN G2:
    Print E.

This is how you can get a list of all the necessary items:

g = [e for e in g iF not e in g2]

quickly will be used by sets:

ss = set (g) - set (G2)

But this method works only if the multiplicity of items is not important.