bpo-34871: inspect: Don't pollute sys.modules (GH-9696) (#9701)

https://bugs.python.org/issue34871
(cherry picked from commit 6f85b826b5)

Co-authored-by: INADA Naoki <methane@users.noreply.github.com>

Lib/inspect.py

@@ -1988,7 +1988,7 @@ def _signature_fromstr(cls, obj, s, skip_bound_arg=True):
         module = sys.modules.get(module_name, None)
         if module:
             module_dict = module.__dict__
-    sys_module_dict = sys.modules
+    sys_module_dict = sys.modules.copy()
 
     def parse_name(node):
         assert isinstance(node, ast.arg)

Misc/NEWS.d/next/Library/2018-10-04-18-46-54.bpo-34871.t3X-dB.rst

@@ -0,0 +1,2 @@
+Fix inspect module polluted ``sys.modules`` when parsing
+``__text_signature__`` of callable.