Add usage printout on empty args

duckargs/__main__.py

@@ -1,6 +1,53 @@
-from duckargs import generate_python_code
+import sys
+from duckargs import generate_python_code, __version__
+
+USAGE = """
+duckargs %s
+
+Erik K. Nyquist 2023
+
+The purpose of duckargs is to save some typing whenever you want to quickly create
+a python program that accepts command line arguments. Just run duckargs with the
+options & arguments that you want your program to accept, with example argument
+values, and duckargs will generate the python code for a program that uses argparse
+to handle those arguments.
+
+For example, running duckargs like this:
+
+
+    duckargs positional_arg -i --intval 12 -d --floatval 99.9 -f --somefile FILE
+
+
+Prints the following python code:
+
+
+    import argparse
+
+    def main():
+	parser = argparse.ArgumentParser(description='',
+					 formatter_class=argparse.ArgumentDefaultsHelpFormatter)
+
+	parser.add_argument('positional_arg', help='a string')
+	parser.add_argument('-i', '--intval', default=12, type=int, help='an int value')
+	parser.add_argument('-d', '--floatval', default=99.9, type=float, help='a float value')
+	parser.add_argument('-f', '--somefile', default=None, type=argparse.FileType(), help='a filename')
+	args = parser.parse_args()
+
+	print(args.positional_arg)
+	print(args.intval)
+	print(args.floatval)
+	print(args.somefile)
+
+    if __name__ == "__main__":
+	main()
+
+""" % __version__
 
 def main():
+    if len(sys.argv) == 1:
+        print(USAGE)
+        return
+
     try:
         print(generate_python_code())
     except (ValueError, RuntimeError) as e: