Implement __radd__ for Quantity and BaseObj (#23)

Fixes #17

Author: brass75

src/cooklang_py/base_objects.py

@@ -128,6 +128,11 @@ def __format__(self, format_spec: str) -> str:
             continue
         return s
 
+    def __radd__(self, other) -> str:
+        if not isinstance(other, str):
+            raise TypeError(f'Cannot add {self} to {other.__class__.__name__}')
+        return f'{other}{self}'
+
 
 class BaseObj:
     """Base Object for Ingredient, Cookware, and Timing"""
@@ -256,6 +261,11 @@ def factory(cls, raw: str):
         name = re.sub(r'\W+$', '', name) or name
         return cls(f'{cls.prefix}{name}', name=name)
 
+    def __radd__(self, other) -> str:
+        if not isinstance(other, str):
+            raise TypeError(f'Cannot add {self} to {other.__class__.__name__}')
+        return f'{other}{self}'
+
 
 class Ingredient(BaseObj):
     """Ingredient"""

tests/test_base_object.py

@@ -68,3 +68,25 @@ def test_formatting_no_unit_or_notes():
     """Test formatting with name and amount"""
     ing = Ingredient(raw='@eggs{3}', name='eggs', quantity='3')
     assert f'{ing:%q[%af %us] %n (%c)}' == '3 eggs ()'
+
+
+def test_quantity_string_addition():
+    """Test string addition"""
+    assert 'Testing: ' + Quantity('1%cup') == 'Testing: 1 c'
+
+
+def test_quantity_quantity_addition():
+    """Test quantity addition"""
+    with pytest.raises(TypeError):
+        Quantity('1%cup') + Quantity('1%cup')
+
+
+def test_baseobj_string_addition():
+    """Test string addition"""
+    assert 'Testing: ' + Ingredient('', name='flour', quantity='1%cup') == 'Testing: flour (1 c)'
+
+
+def test_baseobj_baseobj_addition():
+    """Test quantity addition"""
+    with pytest.raises(TypeError):
+        Ingredient('', name='flour', quantity='1%cup') + Ingredient('', name='flour', quantity='1%cup')