Initial implementation of modular command loading

Issue #943

New class CommandSet can be used to tag a class as a command class. If
the constructor is simple, the object will automatically be instantiated
and loaded.
New register_command decorator to tag any arbitrary function as a
command.

1 files changed, 127 insertions, 0 deletions

diff --git a/examples/modular_commands_main.py b/examples/modular_commands_main.py
new file mode 100644
index 00000000..93dc79ea
--- /dev/null
+++ b/examples/modular_commands_main.py
@@ -0,0 +1,127 @@
+#!/usr/bin/env python
+# coding=utf-8
+"""
+A simple example demonstrating how to integrate tab completion with argparse-based commands.
+"""
+import argparse
+from typing import Dict, List
+
+from cmd2 import Cmd, Cmd2ArgumentParser, CompletionItem, with_argparser
+from cmd2.utils import CompletionError, basic_complete
+from modular_commands.commandset_basic import BasicCompletionCommandSet  # noqa: F401
+from modular_commands.commandset_custominit import CustomInitCommandSet
+
+# Data source for argparse.choices
+food_item_strs = ['Pizza', 'Ham', 'Ham Sandwich', 'Potato']
+
+
+def choices_function() -> List[str]:
+    """Choices functions are useful when the choice list is dynamically generated (e.g. from data in a database)"""
+    return ['a', 'dynamic', 'list', 'goes', 'here']
+
+
+def completer_function(text: str, line: str, begidx: int, endidx: int) -> List[str]:
+    """
+    A tab completion function not dependent on instance data. Since custom tab completion operations commonly
+    need to modify cmd2's instance variables related to tab completion, it will be rare to need a completer
+    function. completer_method should be used in those cases.
+    """
+    match_against = ['a', 'dynamic', 'list', 'goes', 'here']
+    return basic_complete(text, line, begidx, endidx, match_against)
+
+
+def choices_completion_item() -> List[CompletionItem]:
+    """Return CompletionItem instead of strings. These give more context to what's being tab completed."""
+    items = \
+        {
+            1: "My item",
+            2: "Another item",
+            3: "Yet another item"
+        }
+    return [CompletionItem(item_id, description) for item_id, description in items.items()]
+
+
+def choices_arg_tokens(arg_tokens: Dict[str, List[str]]) -> List[str]:
+    """
+    If a choices or completer function/method takes a value called arg_tokens, then it will be
+    passed a dictionary that maps the command line tokens up through the one being completed
+    to their argparse argument name.  All values of the arg_tokens dictionary are lists, even if
+    a particular argument expects only 1 token.
+    """
+    # Check if choices_function flag has appeared
+    values = ['choices_function', 'flag']
+    if 'choices_function' in arg_tokens:
+        values.append('is {}'.format(arg_tokens['choices_function'][0]))
+    else:
+        values.append('not supplied')
+    return values
+
+
+class WithCommandSets(Cmd):
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.sport_item_strs = ['Bat', 'Basket', 'Basketball', 'Football', 'Space Ball']
+
+    def choices_method(self) -> List[str]:
+        """Choices methods are useful when the choice list is based on instance data of your application"""
+        return self.sport_item_strs
+
+    def choices_completion_error(self) -> List[str]:
+        """
+        CompletionErrors can be raised if an error occurs while tab completing.
+
+        Example use cases
+            - Reading a database to retrieve a tab completion data set failed
+            - A previous command line argument that determines the data set being completed is invalid
+        """
+        if self.debug:
+            return self.sport_item_strs
+        raise CompletionError("debug must be true")
+
+    # Parser for example command
+    example_parser = Cmd2ArgumentParser(description="Command demonstrating tab completion with argparse\n"
+                                                    "Notice even the flags of this command tab complete")
+
+    # Tab complete from a list using argparse choices. Set metavar if you don't
+    # want the entire choices list showing in the usage text for this command.
+    example_parser.add_argument('--choices', choices=food_item_strs, metavar="CHOICE",
+                                help="tab complete using choices")
+
+    # Tab complete from choices provided by a choices function and choices method
+    example_parser.add_argument('--choices_function', choices_function=choices_function,
+                                help="tab complete using a choices_function")
+    example_parser.add_argument('--choices_method', choices_method=choices_method,
+                                help="tab complete using a choices_method")
+
+    # Tab complete using a completer function and completer method
+    example_parser.add_argument('--completer_function', completer_function=completer_function,
+                                help="tab complete using a completer_function")
+    example_parser.add_argument('--completer_method', completer_method=Cmd.path_complete,
+                                help="tab complete using a completer_method")
+
+    # Demonstrate raising a CompletionError while tab completing
+    example_parser.add_argument('--completion_error', choices_method=choices_completion_error,
+                                help="raise a CompletionError while tab completing if debug is False")
+
+    # Demonstrate returning CompletionItems instead of strings
+    example_parser.add_argument('--completion_item', choices_function=choices_completion_item, metavar="ITEM_ID",
+                                descriptive_header="Description",
+                                help="demonstrate use of CompletionItems")
+
+    # Demonstrate use of arg_tokens dictionary
+    example_parser.add_argument('--arg_tokens', choices_function=choices_arg_tokens,
+                                help="demonstrate use of arg_tokens dictionary")
+
+    @with_argparser(example_parser)
+    def do_example(self, _: argparse.Namespace) -> None:
+        """The example command"""
+        self.poutput("I do nothing")
+
+
+if __name__ == '__main__':
+    import sys
+
+    print("Starting")
+    command_sets = [CustomInitCommandSet('First argument', 'Second argument')]
+    app = WithCommandSets(command_sets=command_sets)
+    sys.exit(app.cmdloop())