added the generate-setup action

Lib/packaging/run.py

@@ -9,7 +9,7 @@ from copy import copy
 
 from packaging import logger
 from packaging.dist import Distribution
-from packaging.util import _is_archive_file
+from packaging.util import _is_archive_file, generate_setup_py
 from packaging.command import get_command_class, STANDARD_COMMANDS
 from packaging.install import install, install_local_project, remove
 from packaging.database import get_distribution, get_distributions
@@ -38,6 +38,14 @@ Usage: pysetup create
 Create a new Python package.
 """
 
+generate_usage = """\
+Usage: pysetup generate-setup
+   or: pysetup generate-setup --help
+
+Generates a setup.py script for backward-compatibility purposes.
+"""
+
+
 graph_usage = """\
 Usage: pysetup graph dist
    or: pysetup graph --help
@@ -204,6 +212,13 @@ def _create(distpatcher, args, **kw):
     return main()
 
 
+@action_help(generate_usage)
+def _generate(distpatcher, args, **kw):
+    generate_setup_py()
+    print('The setup.py was generated')
+
+
+
 @action_help(graph_usage)
 def _graph(dispatcher, args, **kw):
     name = args[1]
@@ -381,6 +396,7 @@ actions = [
     ('list', 'Search for local projects', _list),
     ('graph', 'Display a graph', _graph),
     ('create', 'Create a Project', _create),
+    ('generate-setup', 'Generates a backward-comptatible setup.py', _generate)
 ]
 
 

Lib/packaging/util.py

@@ -1087,7 +1087,7 @@ def generate_setup_py():
     Raises a PackagingFileError when a setup.py already exists.
     """
     if os.path.exists("setup.py"):
-        raise PackagingFileError("a setup.py file alreadyexists")
+        raise PackagingFileError("a setup.py file already exists")
 
     with open("setup.py", "w", encoding='utf-8') as fp:
         fp.write(_SETUP_TMPL % {'func': getsource(cfg_to_args)})