Add a argparser.

diceware/diceware.py

+import argparse
 import os
 import re
 from random import SystemRandom
@@ -13,6 +14,14 @@ RE_ASCII_CHARS = re.compile('^[a-zA-Z]{2}$')
 SPECIAL_CHARS = "~!#$%^&*()-=+[]\{}:;\"'<>?/0123456789"
 
 
+def handle_options(args):
+    """Handle commandline options.
+    """
+    parser = argparse.ArgumentParser(description="Create a passphrase")
+    args = parser.parse_args(args)
+    return args
+
+
 def get_wordlist(path):
     """Parse file at `path` and build a word list of it.
 

tests/test_diceware.py

 import os
 import pytest
+import sys
 from diceware.diceware import (
-    SRC_DIR, get_wordlist, get_wordlist_path, get_passphrase,
+    SRC_DIR, get_wordlist, get_wordlist_path, get_passphrase, handle_options,
     )
 
 
@@ -53,3 +54,20 @@ class TestDicewareModule(object):
         r1 = get_passphrase()
         r2 = get_passphrase()
         assert r1 != r2
+
+    def test_handle_options(self, capsys):
+        # we can get help
+        with pytest.raises(SystemExit) as exc_info:
+            handle_options(['--help'])
+        assert exc_info.value.code == 0
+        out, err = capsys.readouterr()
+        out = out.replace(
+            os.path.basename(sys.argv[0]), 'diceware')
+        assert out == (
+            'usage: diceware [-h]\n'
+            '\n'
+            'Create a passphrase\n'
+            '\n'
+            'optional arguments:\n'
+            '  -h, --help  show this help message and exit\n'
+            )