python: Provide feature for argparse --[no-]foo options

[secnet.git] / argparseactionnoyes.py

diff --git a/argparseactionnoyes.py b/argparseactionnoyes.py
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+# Python argparse --[no-]foo options
+#
+# Copyright 2012 "Omnifarious" (a user on StackOverFlow)
+# Copyright 2013 "btel" (a user on StackOverFlow)
+#
+# https://stackoverflow.com/questions/9234258/in-python-argparse-is-it-possible-to-have-paired-no-something-something-arg/20422915#20422915
+#
+# CC-BY-SA 4.0
+# by virtue of
+# https://stackoverflow.com/legal/terms-of-service#licensing
+# which says everything is CC-BY-SA and has a link to v4.0
+# (And which is therefore compatible with secnet's GPLv3+)
+#
+# all retrieved 4.11.2019
+
+import argparse
+
+class ActionNoYes(argparse.Action):
+    def __init__(self, option_strings, dest, default=None, required=False, help=None):
+
+        if default is None:
+            raise ValueError('You must provide a default with Yes/No action')
+        if len(option_strings)!=1:
+            raise ValueError('Only single argument is allowed with YesNo action')
+        opt = option_strings[0]
+        if not opt.startswith('--'):
+            raise ValueError('Yes/No arguments must be prefixed with --')
+
+        opt = opt[2:]
+        opts = ['--' + opt, '--no-' + opt]
+        super(ActionNoYes, self).__init__(opts, dest, nargs=0, const=None, 
+                                          default=default, required=required, help=help)
+    def __call__(self, parser, namespace, values, option_strings=None):
+        if option_strings.startswith('--no-'):
+            setattr(namespace, self.dest, False)
+        else:
+            setattr(namespace, self.dest, True)