close files explicit (closes #21610)

Patch by mattip.

Lib/modulefinder.py

@@ -109,14 +109,14 @@ class ModuleFinder:
 
     def run_script(self, pathname):
         self.msg(2, "run_script", pathname)
-        fp = open(pathname, READ_MODE)
+        with open(pathname, READ_MODE) as fp:
             stuff = ("", "r", imp.PY_SOURCE)
             self.load_module('__main__', fp, pathname, stuff)
 
     def load_file(self, pathname):
         dir, name = os.path.split(pathname)
         name, ext = os.path.splitext(name)
-        fp = open(pathname, READ_MODE)
+        with open(pathname, READ_MODE) as fp:
             stuff = (ext, "r", imp.PY_SOURCE)
             self.load_module(name, fp, pathname, stuff)
 
@@ -461,6 +461,8 @@ class ModuleFinder:
         fp, buf, stuff = self.find_module("__init__", m.__path__)
         self.load_module(fqname, fp, buf, stuff)
         self.msgout(2, "load_package ->", m)
+        if fp:
+            fp.close()
         return m
 
     def add_module(self, fqname):