The purpose of this encoding scheme is generating coupon codes. It was originally wrote for ClickCupom, a "deal of the day" website in Brazil.

The standard base32 encoding will generate codes that can be hard to read over the phone (because of characters like I/l/1 and O/0). It also has potential to generate f* words (at least in Portuguese) and the sequence is easy to guess.

This special base 32 scheme has the following attributes:

• to make it easy to read over the phone, chars I/L/O are not used (avoids confusion with 1/0)
• the letter U is not used (to decrease the possibility of f* words)
• the generated codes are not trivial to guess

By default it will generate 5 digit coupon codes, but can generate codes with any number of digits.

Initialize this object with a key made with the characters 'ABCDEFGHJKMNPQRSTWVXYZ0123456789' in random order.

Example:

  >>> c = CouponEncoder('10BEH8G426RADWZVF9JPKX5QMC3YTN7S')
  >>> c.encode(15171013)
  'FS19E'
  >>> c.decode('FS19E')
  15171013
  >>> code, check = c.encode_with_verification(1234)
  ('NH4RZ', '782AV')
  >>> c.is_valid(code, check)
  True
  >>> c.is_valid(code, '782AA')
  False