Fix #12811 by closing files promptly in tabnanny.check. Patch by Anthony Briggs.

Lib/tabnanny.py

@@ -126,6 +126,9 @@ def check(file):
             else: print(file, badline, repr(line))
         return
 
+    finally:
+        f.close()
+
     if verbose:
         print("%r: Clean bill of health." % (file,))
 

Misc/ACKS

@@ -121,6 +121,7 @@ Erik Bray
 Brian Brazil
 Dave Brennan
 Tom Bridgman
+Anthony Briggs
 Tobias Brink
 Richard Brodie
 Michael Broghton

Misc/NEWS

@@ -265,6 +265,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #12811: tabnanny.check() now promptly closes checked files. Patch by
+  Anthony Briggs.
+
 - Issue #6560: The sendmsg/recvmsg API is now exposed by the socket module
   when provided by the underlying platform, supporting processing of
   ancillary data in pure Python code.