def find_filtermode(fname):
"""
Derive enum value from string found in filename.
For downward compatibility, search for both patterns (e.g. '0filter' and
'nofilter').
"""
from constants import FILTER_MODES
names = ["nofilter", "prefilter", "postfilter"]
for enumval, name in zip(sorted(FILTER_MODES.keys()), names):
if "{}filter".format(enumval) in fname or name in fname:
return enumval
raise KeyError("Filter mode could not be deduced from filename!")
