Replace several characters with ligatures.

ligature.py

# -*- coding: utf-8 -*-

import re


_REPLACEMENTS = (
    ('ffi\B', 'ffi', ),
    ('ff\B', 'ff', ),
    ('fi\B', 'fi', ),
    ('fl\B', 'fl', ),
)


def ligature(text):
    for pattern, replacement in _REPLACEMENTS:
        p = re.compile(pattern)
        text = p.sub(replacement, text)
    return text


if __name__ == '__main__':
    import sys
    lines = '\n'.join(sys.stdin.readlines())
    print ligature(lines)