better way to handle config init with invalid arguments

Author: kyuridenamida

atcodertools/codegen/code_gen_config.py

@@ -4,18 +4,23 @@
 INDENT_TYPE_TAB = 'tab'
 
 
-def _verify_indent_type(indent_type: str):
-    # indent_type must be 'space' or 'tab'
-    assert indent_type in [INDENT_TYPE_SPACE, INDENT_TYPE_TAB]
-    return indent_type
+class ConfigInitError(Exception):
+    pass
 
 
 class CodeGenConfig:
     def __init__(self,
                  indent_type: str = INDENT_TYPE_SPACE,
                  indent_width: int = 4,
                  ):
-        self.indent_type = _verify_indent_type(indent_type)
+
+        if indent_type not in [INDENT_TYPE_SPACE, INDENT_TYPE_TAB]:
+            raise ConfigInitError("indent_type must be 'space' or 'tab'")
+
+        if indent_width < 0:
+            raise ConfigInitError("indent_width must be a positive integer")
+
+        self.indent_type = indent_type
         self.indent_width = indent_width
 
     def indent(self, depth):

tests/test_codegen.py

@@ -3,7 +3,7 @@
 import unittest
 import os
 
-from atcodertools.codegen.code_gen_config import CodeGenConfig, INDENT_TYPE_SPACE
+from atcodertools.codegen.code_gen_config import CodeGenConfig, INDENT_TYPE_SPACE, ConfigInitError
 from atcodertools.codegen.code_generator import CodeGenerator
 from atcodertools.codegen.java_code_generator import JavaCodeGenerator
 from atcodertools.codegen.cpp_code_generator import CppCodeGenerator
@@ -88,6 +88,17 @@ def test_load_code_gen_config(self):
         self.assertEqual(8, config.indent_width)
         self.assertEqual(INDENT_TYPE_SPACE, config.indent_type)
 
+    def test_init_code_gen_config_with_invalid_parameters(self):
+        self._expect_error_when_init(indent_type='SPACE', indent_width=4)
+        self._expect_error_when_init(indent_type='space', indent_width=-1)
+
+    def _expect_error_when_init(self, **kwargs):
+        try:
+            CodeGenConfig(**kwargs)
+            self.fail("Must not reach here")
+        except ConfigInitError:
+            pass
+
 
 if __name__ == "__main__":
     unittest.main()