✨ Add optional option

magicparse/fields.py

@@ -18,12 +18,21 @@ def __init__(self, options: dict) -> None:
             PostProcessor.build(item) for item in options.get("post-processors", [])
         ]
 
+        self.optional = options.get("optional", False)
+
         self.transforms = (
             pre_processors + [type_converter] + validators + post_processors
         )
 
     def _process_raw_value(self, raw_value: str):
         value = raw_value
+        if not raw_value:
+            if self.optional:
+                return None
+            else:
+                raise ValueError(
+                    f"{self.key} field is required but the value was empty"
+                )
         for transform in self.transforms:
             value = transform.apply(value)
         return value
@@ -34,10 +43,7 @@ def _read_raw_value(self, row) -> str:
 
     def read_value(self, row):
         raw_value = self._read_raw_value(row)
-        value = raw_value
-        for transform in self.transforms:
-            value = transform.apply(value)
-        return value
+        return self._process_raw_value(raw_value)
 
     @abstractmethod
     def error(self, exception: Exception):

tests/test_fields.py

@@ -86,3 +86,46 @@ def test_columnar_error_format():
         "error": "value 'hello' is not a valid decimal",
         "field-key": "ratio",
     }
+
+
+def test_optional_field():
+    field = DummyField(
+        {
+            "key": "ratio",
+            "type": "decimal",
+            "optional": True,
+            "pre-processors": [
+                {
+                    "name": "replace",
+                    "parameters": {"pattern": "XXX", "replacement": "000"},
+                }
+            ],
+            "post-processors": [{"name": "divide", "parameters": {"denominator": 100}}],
+        }
+    )
+    assert field.read_value("XXX150") == Decimal("1.50")
+    assert field.read_value("") is None
+
+
+def test_required_field():
+    field = DummyField(
+        {
+            "key": "ratio",
+            "type": "decimal",
+            "optional": False,
+        }
+    )
+    assert field.read_value("1.5") == Decimal("1.50")
+
+
+def test_require_field_with_empty_value():
+    field = DummyField(
+        {
+            "key": "pepito",
+            "type": "decimal",
+        }
+    )
+    with pytest.raises(
+        ValueError, match="pepito field is required but the value was empty"
+    ):
+        field.read_value("")