Use the "with" keyword when dealing with file objects

It is good practice to use the "with" keyword when dealing with file objects. This has the advantage that the file is properly closed after its suite finishes, even if an exception is raised on the way. It is also much shorter than writing equivalent try-finally blocks

py/AttackWPA.py

@@ -189,9 +189,8 @@ class AttackWPA(Attack):
         Color.pl("")
         # Check crack result
         if os.path.exists(key_file):
-            f = open(key_file, "r")
-            key = f.read().strip()
-            f.close()
+            with open(key_file, "r") as fid:
+                key = fid.read().strip()
             os.remove(key_file)
 
             Color.pl("{+} {G}Cracked WPA Handshake{W} PSK: {G}%s{W}\n" % key)