[Python-checkins] bpo-37150: Throw ValueError if FileType class object was passed in add_argument (GH-13805)

Miss Islington (bot) webhook-mailer at python.org
Fri Jun 7 16:08:42 EDT 2019

commit: 03d5831a2d62c68654ec223168e574cd546efbf6
branch: master
author: zygocephalus <grrrr at protonmail.com>
committer: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
date: 2019-06-07T13:08:36-07:00

bpo-37150: Throw ValueError if FileType class object was passed in add_argument (GH-13805)

There is a possibility that someone (like me) accidentally will omit parentheses with `FileType` arguments after `FileType`, and parser will contain wrong file until someone will try to use it. 

parser = argparse.ArgumentParser()
parser.add_argument('-x', type=argparse.FileType)


A Misc/NEWS.d/next/Library/2019-06-04-14-44-41.bpo-37150.TTzHxj.rst
M Lib/argparse.py
M Lib/test/test_argparse.py

diff --git a/Lib/argparse.py b/Lib/argparse.py
index ef888f063b32..9a67b41ae00e 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1361,6 +1361,10 @@ def add_argument(self, *args, **kwargs):
         if not callable(type_func):
             raise ValueError('%r is not callable' % (type_func,))
+        if type_func is FileType:
+            raise ValueError('%r is a FileType class object, instance of it'
+                             ' must be passed' % (type_func,))
         # raise an error if the metavar does not match the type
         if hasattr(self, "_get_formatter"):
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index 9d68f40571fe..bcf2cc9b26a3 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -1619,6 +1619,24 @@ def test_open_args(self):
                 m.assert_called_with('foo', *args)
+class TestFileTypeMissingInitialization(TestCase):
+    """
+    Test that add_argument throws an error if FileType class
+    object was passed instead of instance of FileType
+    """
+    def test(self):
+        parser = argparse.ArgumentParser()
+        with self.assertRaises(ValueError) as cm:
+            parser.add_argument('-x', type=argparse.FileType)
+        self.assertEqual(
+            '%r is a FileType class object, instance of it must be passed'
+            % (argparse.FileType,),
+            str(cm.exception)
+        )
 class TestTypeCallable(ParserTestCase):
     """Test some callables as option/argument types"""
diff --git a/Misc/NEWS.d/next/Library/2019-06-04-14-44-41.bpo-37150.TTzHxj.rst b/Misc/NEWS.d/next/Library/2019-06-04-14-44-41.bpo-37150.TTzHxj.rst
new file mode 100644
index 000000000000..c5be46e1e5d3
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-06-04-14-44-41.bpo-37150.TTzHxj.rst
@@ -0,0 +1 @@
+`argparse._ActionsContainer.add_argument` now throws error, if someone accidentally pass FileType class object instead of instance of FileType as `type` argument
\ No newline at end of file

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