SCC: Handle unrecognized SCC codes in SccWord.get_channel()

#428

src/main/python/ttconv/scc/word.py

@@ -119,8 +119,8 @@ def is_code(self) -> bool:
 
  def get_channel(self) -> Optional[SccChannel]:
  """Returns the caption channel, if the word is an SCC code"""
- if self.is_code():
- if isinstance(self.code, SccPreambleAddressCode):
-  return self.code.get_channel()
- return self.code.get_channel(self.value)
- return None
+ if self.code is None:
+ return None
+ if isinstance(self.code, SccPreambleAddressCode):
+ return self.code.get_channel()
+ return self.code.get_channel(self.value)

src/test/python/test_scc_word.py

@@ -29,6 +29,7 @@
 
 import unittest
 
+from ttconv.scc.codes import SccChannel
 from ttconv.scc.codes.control_codes import SccControlCode
 from ttconv.scc.codes.extended_characters import SccExtendedCharacter
 from ttconv.scc.codes.mid_row_codes import SccMidRowCode
@@ -136,3 +137,26 @@ def test_scc_word_get_code(self):
  self.assertEqual(None, SccWord.from_str("2065").get_code()) # " e"
  self.assertEqual(None, SccWord.from_str("6c69").get_code()) # "li"
  self.assertEqual(None, SccWord.from_str("742e").get_code()) # "t."
+
+ def test_scc_word_get_channel(self):
+ # invalid codes
+ self.assertEqual(None, SccWord.from_value(0x1000).get_channel())
+ self.assertEqual(None, SccWord.from_value(0x1432).get_channel())
+ self.assertEqual(None, SccWord.from_value(0x1d00).get_channel())
+ self.assertEqual(None, SccWord.from_value(0x1f38).get_channel())
+
+ # Preamble Address Code
+ self.assertEqual(SccChannel.CHANNEL_1, SccWord.from_value(0x91d0).get_channel())
+ self.assertEqual(SccChannel.CHANNEL_2, SccWord.from_value(0x99d0).get_channel())
+
+ # Attribute Code
+ self.assertEqual(SccChannel.CHANNEL_1, SccWord.from_value(0x1020).get_channel())
+ self.assertEqual(SccChannel.CHANNEL_2, SccWord.from_value(0x1820).get_channel())
+
+ def test_scc_word_all_values(self):
+ # check that all possible values decode to something
+ for i in range(0x10000):
+ scc_word = SccWord.from_value(i)
+ scc_word.to_text()
+ scc_word.get_code()
+ scc_word.get_channel()