Can now pass template variables into nbkickoff

Change the command-line syntax for `nbkickoff` slightly to use
positional arguments, which is easier to use.

Also allow the caller to specify any number of template variables on the
command line, using a simple `NAME=VALUE` syntax.

nbkickoff/nbkickoff.py

@@ -1,10 +1,9 @@
 #!/usr/bin/env python3
 
-from .__about__ import __summary__
+from .__about__ import (__summary__, __title__)
 import logging
 import os
 from pathlib import Path
-import shutil
 import sys
 import webbrowser
 
@@ -59,19 +58,38 @@ def open_notebook(notebook_file):
         launch_detached_process(sys.executable, '-m', 'notebook', '--NotebookApp.open_browser=True', notebook_file)
 
 
-def kickoff(template_file, target_file):
-    create_notebook_from_template(template_file, target_file, {})
+def kickoff(template_file, target_file, variables):
+    create_notebook_from_template(template_file, target_file, variables)
     open_notebook(target_file)
 
 
 def main():
     import argparse
-    parser = argparse.ArgumentParser(description=__summary__)
-    parser.add_argument('-t', '--template', required=True, help='Template notebook file')
-    parser.add_argument('-f', '--file', required=True, help='Target notebook file to create')
+
+    def parse_template_var(s):
+        if '=' not in s:
+            raise argparse.ArgumentTypeError('Invalid template variable specification: ' + s)
+        parts = s.split('=', 1)
+        return {parts[0]: parts[1]}
+
+    class DictMergeAction(argparse.Action):
+        def __call__(self, p, namespace, values, option_string=None):
+            current_dict = dict()
+            if hasattr(namespace, self.dest) and getattr(namespace, self.dest) is not None:
+                current_dict = getattr(namespace, self.dest)
+            for v in values:
+                current_dict = {**current_dict, **v}
+            setattr(namespace, self.dest, current_dict)
+
+    parser = argparse.ArgumentParser(prog=__title__, description=__summary__)
+    parser.add_argument('template', help='Template notebook file')
+    parser.add_argument('target', help='Target notebook file to create')
+    parser.add_argument('variable', action=DictMergeAction, type=parse_template_var, nargs='*',
+                        help='Template variable in the format NAME=VALUE')
     args = parser.parse_args()
-    kickoff(args.template, args.file)
+    kickoff(args.template, args.target, args.variable)
 
 
 if __name__ == '__main__':
     main()
+