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

Your try/except block didn't work because os.path.isfile does not throw an exception if it fails; it merely returns False.

else clauses for for loops are weird and non-intuitive. Using break to signify that the loop was successful rather than legitimately breaking it is just weird, and contrary to Python's philosophy.

Here's a nice, Pythonic way of doing what you want:

want = lambda f: os.path.isfile(f) and f.endswith(".fna")
valid_files = [f for f in os.listdir(os.curdir) if want(f)]
if len(valid_files) == 0:
    print >>sys.stderr, "failed to find .fna files!"
    sys.exit(1)
for filename in valid_files:
    # do stuff