Use the stdlib's PBKDF2 implementation when available.

This is a bit faster than ours, which is good, because it lets you increase
the iteration counts.

This will be used on Python 3.4+, and, pending the acceptance of PEP466, on
newer Python 2.7s.

django/db/models/expressions.py

@@ -15,9 +15,10 @@ class ExpressionNode(tree.Node):
     MUL = '*'
     DIV = '/'
     POW = '^'
-    MOD = '%%'  # This is a quoted % operator - it is quoted
+    # This is a quoted % operator - it is quoted
     # because it can be used in strings that also
     # have parameter substitution.
+    MOD = '%%'
 
     # Bitwise operators - note that these are generated by .bitand()
     # and .bitor(), the '&' and '|' are reserved for boolean operator

django/utils/crypto.py

@@ -117,7 +117,24 @@ def _long_to_bin(x, hex_format_string):
     return binascii.unhexlify((hex_format_string % x).encode('ascii'))
 
 
-def pbkdf2(password, salt, iterations, dklen=0, digest=None):
+if hasattr(hashlib, "pbkdf2_hmac"):
+    def pbkdf2(password, salt, iterations, dklen=0, digest=None):
+        """
+        Implements PBDF2 with the same API as Django's existing implementation,
+        using the stdlib.
+
+        This is used in Python 3.4 and up.
+        """
+        if digest is None:
+            digest = hashlib.sha256
+        if not dklen:
+            dklen = None
+        password = force_bytes(password)
+        salt = force_bytes(salt)
+        return hashlib.pbkdf2_hmac(
+            digest().name, password, salt, iterations, dklen)
+else:
+    def pbkdf2(password, salt, iterations, dklen=0, digest=None):
         """
         Implements PBKDF2 as defined in RFC 2898, section 5.2