Check that a *type* of file exists in Python

Question

I realize this looks similar to other questions about checking if a file exists, but it is different. I\'m trying to figure out how to check that a type of

Answer 1

The for statement in Python has a little-known else clause:

for filename in filenames:
    if os.path.isfile(filename) and filename.endswith(".fna"):
        # do stuff
        break
else:
    sys.stderr.write ('No database file found. Exiting program. \n')
    sys.exit(-1)

The else clause is run only if the for statement runs through its whole enumeration without executing the break inside the loop.