Added path_complete() static method for local file system path completion

The edit, load, and shell commands now all use this for their tab completion.

Additionally, end users can easily wire it up for use with any of their custom commands.

Author: tleonhardt

cmd2.py

@@ -1327,6 +1327,38 @@ def help_shell(self):
     Usage:  shell cmd"""
         self.stdout.write("{}\n".format(help_str))
 
+    @staticmethod
+    def path_complete(line):
+        """Method called to complete an input line by local file system path completion.
+
+        :param line: str - the current input line with leading whitespace removed
+        :return: List[str] - a list of possible tab completions
+        """
+        path = line.split()[-1]
+        if not path:
+            path = '.'
+
+        dirname, rest = os.path.split(path)
+        real_dir = os.path.expanduser(dirname)
+
+        path_completions = glob.glob(os.path.join(real_dir, rest) + '*')
+
+        # Strip off everything but the final part of the completion
+        completions = [os.path.basename(c) for c in path_completions]
+        return completions
+
+    # noinspection PyUnusedLocal
+    def complete_shell(self, text, line, begidx, endidx):
+        """Handles completion of arguments for the shell command.
+
+        :param text: str - the string prefix we are attempting to match (all returned matches must begin with it)
+        :param line: str - the current input line with leading whitespace removed
+        :param begidx: str - the beginning indexe of the prefix text
+        :param endidx: str - the ending index of the prefix text
+        :return: List[str] - a list of possible tab completions
+        """
+        return self.path_complete(line)
+
     def do_py(self, arg):
         """
         py <command>: Executes a Python command.
@@ -1551,6 +1583,18 @@ def help_edit(self):
                   pyparsing.Optional(pyparsing.Word(legalChars + '/\\'))("fname") +
                   pyparsing.stringEnd)
 
+    # noinspection PyUnusedLocal
+    def complete_edit(self, text, line, begidx, endidx):
+        """Handles completion of arguments for the edit command.
+
+        :param text: str - the string prefix we are attempting to match (all returned matches must begin with it)
+        :param line: str - the current input line with leading whitespace removed
+        :param begidx: str - the beginning indexe of the prefix text
+        :param endidx: str - the ending index of the prefix text
+        :return: List[str] - a list of possible tab completions
+        """
+        return self.path_complete(line)
+
     def do_save(self, arg):
         """Saves command(s) from history to file.
 
@@ -1688,6 +1732,18 @@ def help_load(self):
 Script should contain one command per line, just like command would be typed in console."""
         self.stdout.write("{}\n".format(help_str))
 
+    # noinspection PyUnusedLocal
+    def complete_load(self, text, line, begidx, endidx):
+        """Handles completion of arguments for the load command.
+
+        :param text: str - the string prefix we are attempting to match (all returned matches must begin with it)
+        :param line: str - the current input line with leading whitespace removed
+        :param begidx: str - the beginning indexe of the prefix text
+        :param endidx: str - the ending index of the prefix text
+        :return: List[str] - a list of possible tab completions
+        """
+        return self.path_complete(line)
+
     def do_run(self, arg):
         """run [arg]: re-runs an earlier command