text: # Copyright (c) 2014 Adafruit Industries
  # Author: Tony DiCola
  
  # Permission is hereby granted, free of charge, to any person obtaining a copy
  # of this software and associated documentation files (the "Software"), to deal
  # in the Software without restriction, including without limitation the rights
  # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  # copies of the Software, and to permit persons to whom the Software is
  # furnished to do so, subject to the following conditions:
  
  # The above copyright notice and this permission notice shall be included in all
  # copies or substantial portions of the Software.
  
  # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  # AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  # SOFTWARE.
  
  # This is a direct copy of what's in the Adafruit Python GPIO library:
  #  https://raw.githubusercontent.com/adafruit/Adafruit_Python_GPIO/master/Adafruit_GPIO/Platform.py
  # TODO: Add dependency on Adafruit Python GPIO and use its platform detect
  # functions.
  
  import platform
  import re
  
  # Platform identification constants.
  UNKNOWN          = 0
  RASPBERRY_PI     = 1
  BEAGLEBONE_BLACK = 2
  
  
  def platform_detect():
      """Detect if running on the Raspberry Pi or Beaglebone Black and return the
      platform type.  Will return RASPBERRY_PI, BEAGLEBONE_BLACK, or UNKNOWN."""
      # Handle Raspberry Pi
      pi = pi_version()
      if pi is not None:
          return RASPBERRY_PI
  
      # Handle Beaglebone Black
      # TODO: Check the Beaglebone Black /proc/cpuinfo value instead of reading
      # the platform.
      plat = platform.platform()
      if plat.lower().find('armv7l-with-debian') > -1:
          return BEAGLEBONE_BLACK
      elif plat.lower().find('armv7l-with-ubuntu') > -1:
          return BEAGLEBONE_BLACK
      elif plat.lower().find('armv7l-with-glibc2.4') > -1:
          return BEAGLEBONE_BLACK
      elif plat.lower().find('armv7l-with-arch') > -1:
          return BEAGLEBONE_BLACK
  
      # Couldn't figure out the platform, just return unknown.
      return UNKNOWN
  
  
  def pi_revision():
      """Detect the revision number of a Raspberry Pi, useful for changing
      functionality like default I2C bus based on revision."""
      # Revision list available at: http://elinux.org/RPi_HardwareHistory#Board_Revision_History
      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, flags=re.IGNORECASE)
              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, throw an exception.
          raise RuntimeError('Could not determine Raspberry Pi revision.')
  
  
  def pi_version():
      """Detect the version of the Raspberry Pi.  Returns either 1, 2, 3 or
      None depending on if it's a Raspberry Pi 1 (model A, B, A+, B+),
      Raspberry Pi 2 (model B+), Raspberry Pi 3 or not a Raspberry Pi.
      """
      # Check /proc/cpuinfo for the Hardware field value.
      # 2708 is pi 1
      # 2709 is pi 2
      # 2835 is pi 3
      # Anything else is not a pi.
      with open('/proc/cpuinfo', 'r') as infile:
          cpuinfo = infile.read()
      # Match a line like 'Hardware   : BCM2709'
      match = re.search('^Hardware\s+:\s+(\w+)$', cpuinfo,
                        flags=re.MULTILINE | re.IGNORECASE)
      if not match:
          # Couldn't find the hardware, assume it isn't a pi.
          return None
      if match.group(1) == 'BCM2708':
          # Pi 1
          return 1
      elif match.group(1) == 'BCM2709':
          # Pi 2
          return 2
      elif match.group(1) == 'BCM2835':
          # Pi 3
          return 3
      elif match.group(1) == 'BCM2837':
          # Pi 3 b+
          return 3
      else:
          # Something else, not a pi.
          return None
  