argparse

$ ./bencode -h
usage: bencode.py [-h] [-s NAME] [-i] [-n] [-p] [-l] [-r] [-t] [--max-width N]
                  [--indent N] [-m] [--show-hits] [-g] [--graph-rule NAME]
                  [FILE]

Parse Bencoded input

positional arguments:
  FILE                  parse the given file, if not supplied, parse stdin

optional arguments:
  -h, --help            show this help message and exit
  -s NAME, --start NAME
                        call this rule first
  -i, --ignore-case     ignore case when matching literal termials
  -n, --no-skip         don't call skip()
  -p, --profile         profile the parse (cProfile), print the results
  -l, --list-rules      print an alphabetized table of all rule names in the
                        grammar
  -r, --repl            start a simpl repl

tracing:
  -t, --trace           print a trace as the parser is working
  --max-width N         truncate the trace output at the given column, default
                        is 78
  --indent N            trace indent for nested calls, default is 3 spaces

memoization:
  -m, --memoize         memoize each rule
  --show-hits           print the number of memoization cache hits

graphviz:
  -g, --graph           display the internal Expr tree of every rule with
                        graphviz
  --graph-rule NAME     display the internal Expr tree of the given rule name
                        with graphviz (case-sensitve)

All arguments are optional. If none are supplied, parse stdin.