Raise an exception when assembly fails

py65/assembler.py

@@ -68,7 +68,7 @@ class Assembler:
     def assemble(self, statement, pc=0000):
         """ Assemble the given assembly language statement.  If the statement
         uses relative addressing, the program counter (pc) must also be given.
-        The result is a list of bytes, or None if the assembly failed.
+        The result is a list of bytes.  Raises when assembly fails.
         """
         opcode, operands = self.normalize_and_split(statement)
 
@@ -99,7 +99,7 @@ class Assembler:
                 return bytes
 
         # assembly failed
-        return None
+        raise SyntaxError(statement)
 
     def normalize_and_split(self, statement):
         """ Given an assembly language statement like "lda $c12,x", normalize

py65/tests/test_assembler.py

@@ -5,6 +5,18 @@ from py65.assembler import Assembler
 from py65.utils.addressing import AddressParser
 
 class AssemblerTests(unittest.TestCase):
+    def test_assemble_bad_syntax_raises_syntaxerror(self):
+        self.assertRaises(SyntaxError,
+                          self.assemble, 'foo')
+
+    def test_assemble_bad_label_raises_keyerror(self):
+        self.assertRaises(KeyError,
+                          self.assemble, 'lda foo')
+
+    def test_assemble_bad_number_raises_overflowerror(self):
+        self.assertRaises(OverflowError,
+                          self.assemble, 'lda #$fff')
+
     def test_assembles_00(self):
         self.assertEqual([0x00],
                          self.assemble('BRK'))