Suggest most simillar command

cmd2/cmd2.py

@@ -141,6 +141,7 @@
     Settable,
     get_defining_class,
     strip_doc_annotations,
+    suggest_similar,
 )
 
 # Set up readline
@@ -236,6 +237,7 @@ def __init__(
         command_sets: Optional[Iterable[CommandSet]] = None,
         auto_load_commands: bool = True,
         allow_clipboard: bool = True,
+        suggest_similar_command: bool = False,
     ) -> None:
         """An easy but powerful framework for writing line-oriented command
         interpreters. Extends Python's cmd package.
@@ -530,6 +532,9 @@ def __init__(
         # Add functions decorated to be subcommands
         self._register_subcommands(self)
 
+        self.suggest_similar_command = suggest_similar_command
+        self.default_suggestion_message = "Did you mean {}?"
+
     def find_commandsets(self, commandset_type: Type[CommandSet], *, subclass_match: bool = False) -> List[CommandSet]:
         """
         Find all CommandSets that match the provided CommandSet type.
@@ -2968,11 +2973,17 @@ def default(self, statement: Statement) -> Optional[bool]:  # type: ignore[overr
             return self.do_shell(statement.command_and_args)
         else:
             err_msg = self.default_error.format(statement.command)
-
+            if self.suggest_similar_command:
+                suggested_command = self._suggest_similar_command(statement.command)
+                if suggested_command:
+                    err_msg = err_msg + ' ' + self.default_suggestion_message.format(suggested_command)
             # Set apply_style to False so default_error's style is not overridden
             self.perror(err_msg, apply_style=False)
             return None
 
+    def _suggest_similar_command(self, command: str) -> Optional[str]:
+        return suggest_similar(command, self.get_visible_commands())
+
     def read_input(
         self,
         prompt: str,

cmd2/utils.py

@@ -12,6 +12,7 @@
 import sys
 import threading
 import unicodedata
+from difflib import SequenceMatcher
 from enum import (
     Enum,
 )
@@ -1262,3 +1263,36 @@ def strip_doc_annotations(doc: str) -> str:
         elif found_first:
             break
     return cmd_desc
+
+
+def similarity_function(s1: str, s2: str) -> float:
+    # The ratio from s1,s2 may be different to s2,s1. We keep the max.
+    # See https://docs.python.org/3/library/difflib.html#difflib.SequenceMatcher.ratio
+    return max(SequenceMatcher(None, s1, s2).ratio(), SequenceMatcher(None, s2, s1).ratio())
+
+
+MIN_SIMIL_TO_CONSIDER = 0.7
+
+
+def suggest_similar(requested_command: str, options: Iterable[str],
+                    similarity_function_to_use: Optional[Callable[[str, str], float]] = None) -> Optional[str]:
+    """
+    Given a requested command and an iterable of possible options
+    returns the most similar (if any is similar)
+
+    :param requested_command: The command entered by the user
+    :param options: The list of avaiable commands to search for the most similar
+    :param similarity_function_to_use: An optional callable to use to compare commands
+    :returns The most similar command or None if no one is similar
+
+    """
+    proposed_command = None
+    best_simil = MIN_SIMIL_TO_CONSIDER
+    requested_command_to_compare = requested_command.lower()
+    similarity_function_to_use = similarity_function_to_use or similarity_function
+    for each in options:
+        simil = similarity_function_to_use(each.lower(), requested_command_to_compare)
+        if best_simil < simil:
+            best_simil = simil
+            proposed_command = each
+    return proposed_command

docs/api/cmd.rst

@@ -72,3 +72,9 @@ cmd2.Cmd
         the operating system pasteboard. If ``False``, this capability will not
         be allowed. See :ref:`features/clipboard:Clipboard Integration` for more
         information.
+
+    .. attribute:: suggest_similar_command
+
+        If ``True``, ``cmd2`` will suggest the most similar command when the user
+        types a command that does not exist.
+        Default: ``False``.

docs/api/utils.rst

@@ -97,3 +97,5 @@ Miscellaneous
 .. autofunction:: cmd2.utils.alphabetical_sort
 
 .. autofunction:: cmd2.utils.natural_sort
+
+.. autofunction:: cmd2.utils.suggest_similar

tests/test_cmd2.py

@@ -323,6 +323,16 @@ def test_base_error(base_app):
     assert "is not a recognized command" in err[0]
 
 
+def test_base_error_suggest_command(base_app):
+    try:
+        old_suggest_similar_command = base_app.suggest_similar_command
+        base_app.suggest_similar_command = True
+        out, err = run_cmd(base_app, 'historic')
+        assert "history" in err[0]
+    finally:
+        base_app.suggest_similar_command = old_suggest_similar_command
+
+
 def test_run_script(base_app, request):
     test_dir = os.path.dirname(request.module.__file__)
     filename = os.path.join(test_dir, 'script.txt')

tests/test_utils.py

@@ -872,3 +872,37 @@ def test_find_editor_not_specified():
     with mock.patch.dict(os.environ, {'PATH': 'fake_dir'}, clear=True):
         editor = cu.find_editor()
     assert editor is None
+
+
+def test_similarity():
+    suggested_command = cu.suggest_similar("comand", ["command", "UNRELATED", "NOT_SIMILAR"])
+    assert suggested_command == "command"
+    suggested_command = cu.suggest_similar("command", ["COMMAND", "acommands"])
+    assert suggested_command == "COMMAND"
+
+
+def test_similarity_without_good_canididates():
+    suggested_command = cu.suggest_similar("comand", ["UNRELATED", "NOT_SIMILAR"])
+    assert suggested_command is None
+    suggested_command = cu.suggest_similar("comand", [])
+    assert suggested_command is None
+
+
+def test_similarity_overwrite_function():
+    suggested_command = cu.suggest_similar("test", ["history", "test"])
+    assert suggested_command == 'test'
+
+    def custom_similarity_function(s1, s2):
+        return 1.0 if 'history' in (s1, s2) else 0.0
+
+    suggested_command = cu.suggest_similar("test", ["history", "test"],
+                                           similarity_function_to_use=custom_similarity_function)
+    assert suggested_command == 'history'
+
+    suggested_command = cu.suggest_similar("history", ["history", "test"],
+                                           similarity_function_to_use=custom_similarity_function)
+    assert suggested_command == 'history'
+
+    suggested_command = cu.suggest_similar("test", ["test"],
+                                           similarity_function_to_use=custom_similarity_function)
+    assert suggested_command is None