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

https://bugs.python.org/issue34871

Author: methane

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.