diff -u ply/yacc.py ply.mine/yacc.py

--- ply/yacc.py	2011-02-18 04:52:28.000000000 +0100

+++ ply.mine/yacc.py	2017-03-03 16:01:13.609507492 +0100

@@ -2794,24 +2794,20 @@

     # Compute a signature over the grammar

     def signature(self):

+        parts = []

         try:

-            from hashlib import md5

-        except ImportError:

-            from md5 import md5

-        try:

-            sig = md5()

             if self.start:

-                sig.update(self.start.encode('latin-1'))

+                parts.append(self.start)

             if self.prec:

-                sig.update("".join(["".join(p) for p in self.prec]).encode('latin-1'))

+                parts.append(''.join([''.join(p) for p in self.prec]))

             if self.tokens:

-                sig.update(" ".join(self.tokens).encode('latin-1'))

+                parts.append(' '.join(self.tokens))

             for f in self.pfuncs:

                 if f[3]:

-                    sig.update(f[3].encode('latin-1'))

-        except (TypeError,ValueError):

+                    parts.append(f[3])

+        except (TypeError, ValueError):

             pass

-        return sig.digest()

+        return ''.join(parts)

     # -----------------------------------------------------------------------------

     # validate_file()