Fix inspect.getmodule to use a copy of sys.modules for iteration (#13487).

This fixes a regression compared to 2.x, where sys.modules.items()
returns a copy, as indicated by a comment in the source.  Diagnosis and
patch by Erik Tollerud.

Lib/inspect.py

@@ -483,7 +483,7 @@ def getmodule(object, _filename=None):
         return sys.modules.get(modulesbyfile[file])
     # Update the filename to module name cache and check yet again
     # Copy sys.modules in order to cope with changes while iterating
-    for modname, module in sys.modules.items():
+    for modname, module in list(sys.modules.items()):
         if ismodule(module) and hasattr(module, '__file__'):
             f = module.__file__
             if f == _filesbymodname.get(modname, None):

Misc/ACKS

@@ -905,6 +905,7 @@ Christian Tismer
 Frank J. Tobin
 R Lindsay Todd
 Bennett Todd
+Erik Tollerud
 Matias Torchinsky
 Sandro Tosi
 Richard Townsend

Misc/NEWS

@@ -87,6 +87,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #13487: Make inspect.getmodule robust against changes done to
+  sys.modules while it is iterating over it.
+
 - Issue #12618: Fix a bug that prevented py_compile from creating byte
   compiled files in the current directory.  Initial patch by Sjoerd de Vries.