On Friday, while trying to work with standard input (stdin) and command-line arguments (argv), I accidentally wrote an almost-quine (a program that produces its own source code as output). I've removed a few debugging print lines, unused functions, etc. to give you this cleaned-up version:

$ ./script.py testfile.txt
#!/usr/bin/python

import sys

def intakefromfile():
    b = sys.argv
    if len(b) > 0:
        with open(b[0], 'r') as f:
            filedata = f.read()
    return filedata

if __name__ == '__main__':
    print intakefromfile()

Explanation: I meant to have script.py grab the first argument to script.py, assume it was a file, and open and print it. However, I failed to actually check the behavior of sys.argv ahead of time; turns out that the actual first item in sys.argv is, in this case, "script.py", not "testfile.txt". You can try this out yourself, and verify that you'll get the same output whether or not you include testfile.txt as an argument. Off-by-one error. I should have had the with open(b[0], 'r') bit try to open(b[1], 'r') instead.

Reading a file is cheating in real quine competitions. But I still found this pretty funny.