Make double-dash options taking priority oved single-dash long options.

Author: serhiy-storchaka

Doc/library/argparse.rst

@@ -1322,8 +1322,12 @@ attribute is determined by the ``dest`` keyword argument of
 
 For optional argument actions, the value of ``dest`` is normally inferred from
 the option strings.  :class:`ArgumentParser` generates the value of ``dest`` by
-taking the first long option string and stripping away the initial ``-``
-characters.  If no long option strings were supplied, ``dest`` will be derived from
+taking the first double-dash long option string and stripping away the initial
+``-`` characters.
+If no double-dash long option strings were supplied, ``dest`` will be derived
+from the first single-dash long option string by stripping the initial ``-``
+character.
+If no long option strings were supplied, ``dest`` will be derived from
 the first short option string by stripping the initial ``-`` character.  Any
 internal ``-`` characters will be converted to ``_`` characters to make sure
 the string is a valid attribute name.  The examples below illustrate this

Lib/argparse.py

@@ -1660,7 +1660,6 @@ def _get_positional_kwargs(self, dest, **kwargs):
     def _get_optional_kwargs(self, *args, **kwargs):
         # determine short and long option strings
         option_strings = []
-        long_option_strings = []
         for option_string in args:
             # error on strings that don't start with an appropriate prefix
             if not option_string[0] in self.prefix_chars:
@@ -1672,16 +1671,22 @@ def _get_optional_kwargs(self, *args, **kwargs):
         # infer destination, '--foo-bar' -> 'foo_bar' and '-x' -> 'x'
         dest = kwargs.pop('dest', None)
         if dest is None:
-            short_option_dest = None
+            priority = 0
             for option_string in option_strings:
-                if len(option_string) > 2:
-                    # long option: '--foo' or '-foo' -> 'foo'
+                if len(option_string) <= 2:
+                    # short option: '-x' -> 'x'
+                    if priority < 1:
+                        dest = option_string.lstrip(self.prefix_chars)
+                        priority = 1
+                elif option_string[1] not in self.prefix_chars:
+                    # single-dash long option: '-foo' -> 'foo'
+                    if priority < 2:
+                        dest = option_string.lstrip(self.prefix_chars)
+                        priority = 2
+                else:
+                    # two-dash long option: '--foo' -> 'foo'
                     dest = option_string.lstrip(self.prefix_chars)
                     break
-                # short option: '-x' -> 'x'
-                if not short_option_dest:
-                    short_option_dest = option_string.lstrip(self.prefix_chars)
-            dest = dest or short_option_dest
             if not dest:
                 msg = f'dest= is required for options like {repr(option_strings)[1:-1]}'
                 raise TypeError(msg)

Lib/test/test_argparse.py

@@ -582,9 +582,9 @@ class TestOptionalsDest(ParserTestCase):
     """Tests various means of setting destination"""
 
     argument_signatures = [
-        Sig('-x', '--foo-bar'),
+        Sig('-x', '-foobar', '--foo-bar', '-barfoo', '-X'),
         Sig('--baz', dest='zabbaz'),
-        Sig('-y', '-qux'),
+        Sig('-y', '-qux', '-Y'),
         Sig('-z'),
     ]
     failures = ['a']