code: def activate_user(activation_key):
      
      # Make sure the key we're trying conforms to the pattern of a
      # SHA1 hash; if it doesn't, no point trying to look it up in
      # the database.
      if SHA1_RE.search(activation_key):
          try:
              profile = RegistrationProfile.objects.get(
                  activation_key=activation_key)
          except RegistrationProfile.DoesNotExist:
              return False
          if not profile.activation_key_expired():
              user = profile.user
              user.is_active = True
              user.save()
              profile.activation_key = RegistrationProfile.ACTIVATED
              profile.save()
              return user
      return False
docs: Validate an activation key and activate the corresponding
      ``User`` if valid.
      If the key is valid and has not expired, return the ``User``
      after activating.
      If the key is not valid or has expired, return ``False``.
      If the key is valid but the ``User`` is already active,
      return ``False``.
      To prevent reactivation of an account which has been
      deactivated by site administrators, the activation key is
      reset to the string constant ``RegistrationProfile.ACTIVATED``
      after successful activation.