Update I2C revision detection to use logic from newer GPIO library. Fixes bug with A+ misidentification.

Author: tdicola

Adafruit_I2C/Adafruit_I2C.py

@@ -1,5 +1,5 @@
 #!/usr/bin/python
-
+import re
 import smbus
 
 # ===========================================================================
@@ -11,14 +11,21 @@ class Adafruit_I2C(object):
   @staticmethod
   def getPiRevision():
     "Gets the version number of the Raspberry Pi board"
-    # Courtesy quick2wire-python-api
-    # https://github.com/quick2wire/quick2wire-python-api
-    # Updated revision info from: http://elinux.org/RPi_HardwareHistory#Board_Revision_History
+    # Revision list available at: http://elinux.org/RPi_HardwareHistory#Board_Revision_History
     try:
-      with open('/proc/cpuinfo','r') as f:
-        for line in f:
-          if line.startswith('Revision'):
-            return 1 if line.rstrip()[-1] in ['2','3'] else 2
+      with open('/proc/cpuinfo', 'r') as infile:
+        for line in infile:
+          # Match a line of the form "Revision : 0002" while ignoring extra
+          # info in front of the revsion (like 1000 when the Pi was over-volted).
+          match = re.match('Revision\s+:\s+.*(\w{4})$', line)
+          if match and match.group(1) in ['0000', '0002', '0003']:
+            # Return revision 1 if revision ends with 0000, 0002 or 0003.
+            return 1
+          elif match:
+            # Assume revision 2 if revision ends with any other 4 chars.
+            return 2
+        # Couldn't find the revision, assume revision 0 like older code for compatibility.
+        return 0
     except:
       return 0