renumbering chapters >= 19

24-class-metaprog/metabunch/pre3.6/bunch.py

@@ -0,0 +1,41 @@
+import collections
+import warnings
+
+class MetaBunch(type):
+    def __prepare__(name, *bases, **kwargs):
+        return collections.OrderedDict()
+
+    def __new__(meta_cls, cls_name, bases, cls_dict):
+        def __init__(self, **kw):
+            for k in self.__defaults__:
+                setattr(self, k, self.__defaults__[k])
+            for k in kw:
+                setattr(self, k, kw[k])
+
+        def __repr__(self):
+            rep = ['{}={!r}'.format(k, getattr(self, k))
+                    for k in self.__defaults__
+                    if getattr(self, k) != self.__defaults__[k]
+                  ]
+            return '{}({})'.format(cls_name, ', '.join(rep))
+
+        new_dict = { '__slots__':[], 
+            '__defaults__':collections.OrderedDict(),
+            '__init__':__init__, '__repr__':__repr__, }
+
+        for k in cls_dict:
+            if k.startswith('__') and k.endswith('__'):
+                if k in new_dict:
+                    warnings.warn(
+                        "Can't set attr {!r} in bunch-class {!r}".
+                        format(k, cls_name))
+                else:
+                    new_dict[k] = cls_dict[k]
+            else:
+                new_dict['__slots__'].append(k)
+                new_dict['__defaults__'][k] = cls_dict[k]
+
+        return super().__new__(meta_cls, cls_name, bases, new_dict)
+
+class Bunch(metaclass=MetaBunch):
+    pass

24-class-metaprog/metabunch/pre3.6/bunch_test.py

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+import pytest
+
+from bunch import Bunch
+
+class Point(Bunch):
+    """ A point has x and y coordinates, defaulting to 0.0, 
+        and a color, defaulting to 'gray'—and nothing more, 
+        except what Python and the metaclass conspire to add, 
+        such as __init__ and __repr__
+    """
+    x = 0.0
+    y = 0.0
+    color = 'gray'
+
+
+def test_init_defaults():
+    p = Point()
+    assert repr(p) == 'Point()'
+
+
+def test_init():
+    p = Point(x=1.2, y=3.4, color='red')
+    assert repr(p) == "Point(x=1.2, y=3.4, color='red')"
+
+
+def test_init_wrong_argument():
+    with pytest.raises(AttributeError) as exc:
+        p = Point(x=1.2, y=3.4, flavor='coffee')
+    assert "no attribute 'flavor'" in str(exc.value)
+
+
+def test_slots():
+    p = Point()
+    with pytest.raises(AttributeError) as exc:
+        p.z = 5.6
+    assert "no attribute 'z'" in str(exc.value)
+
+