Merge pull request #1 from InvestmentSystems/dev

0.2.0

README.md

@@ -1,5 +1,5 @@
 # class_only_design
-[![Build Status](https://travis-ci.com/ForeverWintr/class_only_design.svg?branch=master)](https://travis-ci.com/ForeverWintr/class_only_design) [![codecov](https://codecov.io/gh/ForeverWintr/class_only/branch/master/graph/badge.svg)](https://codecov.io/gh/ForeverWintr/class_only)
+[![Build Status](https://travis-ci.com/InvestmentSystems/class_only_design.svg?branch=master)](https://travis-ci.com/InvestmentSystems/class_only_design) [![codecov](https://codecov.io/gh/ForeverWintr/class_only/branch/master/graph/badge.svg)](https://codecov.io/gh/ForeverWintr/class_only)
 
 ## Tools for class only design. 
 

class_only_design.wpr

@@ -1,9 +1,19 @@
 #!wing
-#!version=6.0
+#!version=7.0
 ##################################################################
-# Wing IDE project file                                          #
+# Wing project file                                              #
 ##################################################################
 [project attributes]
+console.toolbox = [{'autosave': False,
+                    'id': 'cmd-NYHX8PCN0FQtdIJK',
+                    'io_encoding': None,
+                    'key_binding': None,
+                    'line_mode': True,
+                    'loc': u'/Users/tomrutherford/Documents/nonDBCode/class_only_design/class_only_design/meta.py',
+                    'pseudo_tty': False,
+                    'raise_panel': True,
+                    'shared': False,
+                    'title': None}]
 proj.directory-list = [{'dirloc': loc('class_only_design'),
                         'excludes': (),
                         'filter': u'*',

class_only_design/__init__.py

@@ -4,7 +4,8 @@
 
 __author__ = """Tom Rutherford"""
 __email__ = "[email protected]"
-__version__ = "0.1.4"
+__version__ = "0.2.0"
 
-from class_only_design.core import class_only
-from class_only_design.core import constant
+from class_only_design.api import class_only
+from class_only_design.api import constant
+from class_only_design.api import namespace

class_only_design/api.py

@@ -0,0 +1,46 @@
+import functools
+
+from class_only_design.meta import OnlyMeta
+from class_only_design.meta import MetaNamespace
+from class_only_design import util
+
+
+def class_only(cls):
+    """
+    Class only is a class decorator that disallows instantiation or state change on a class object.
+    """
+    classdict = {k: v for k, v in cls.__dict__.items()}
+    new = OnlyMeta(cls.__name__, cls.__bases__, classdict)
+
+    return new
+
+
+class constant:
+    """
+    A method decorator similar to @property but for use on class only classes. The decorated method
+    is only called once. Subsequent calls simply return the stored value. This is usefull for
+    declaring a class level constant that is not actually created until it's used.
+    """
+
+    def __init__(self, method):
+        self.method = method
+        self._value = None
+
+    def __get__(self, instance, cls):
+        if not self._value:
+            self._value = self.method(cls)
+        return self._value
+
+
+def namespace(cls):
+    """
+    Class only is a class decorator that disallows instantiation or state change on a class object.
+    """
+
+    classdict = {k: v for k, v in cls.__dict__.items()}
+    classdict["_initializing_"] = True
+    new = MetaNamespace(cls.__name__, cls.__bases__, classdict)
+    new.nameof = util.KeyGetter(new)
+    del new._initializing_
+
+    return new

class_only_design/constants.py

@@ -0,0 +1,3 @@
+
+# These names are reserved for use by the namespace class machinery. They cannot appear in namespace classes.
+RESERVED_NAMES = {"nameof"}

class_only_design/meta.py

@@ -0,0 +1,62 @@
+from class_only_design import constants
+from class_only_design import util
+
+# This is inserted into decorated classes. Note, __new__ is implicitly converted to a staticmethod
+# during class creation. I'm doing so explicitly here so I have a reference I can check later. This
+# seems to prevent the implicit transformation, but I'm not sure if that's an implementation
+# detail.
+@staticmethod
+def __new__(*args, **kwargs):
+    raise TypeError("Class Only classes cannot be instantiated")
+
+
+class OnlyMeta(type):
+    def __new__(cls, name, bases, classdict):
+
+        if "__init__" in classdict:
+            raise TypeError("Class Only classes cannot define __init__")
+        if classdict.get("__new__") not in (__new__, None):
+            raise TypeError("Class Only classes cannot define __new__")
+
+        # Disallow bases that have __new__ or __init__ defined
+        for b in bases:
+            if not isinstance(b, cls):
+                if b.__init__ is not object.__init__:
+                    raise TypeError("Class Only classes cannot define __init__", b)
+                if b.__new__ is not object.__new__:
+                    raise TypeError("Class Only classes cannot define __new__", b)
+
+        # Insert our own __new__
+        classdict["__new__"] = __new__
+        return super().__new__(cls, name, bases, classdict)
+
+    def __setattr__(cls, name, arg):
+        if not getattr(cls, "_initializing_", False):
+            raise TypeError("Class Only classes are immutable")
+        return super().__setattr__(name, arg)
+
+
+class MetaNamespace(OnlyMeta):
+    def __new__(cls, name, bases, classdict):
+        # disallow reserved names
+        bad_names = classdict.keys() & constants.RESERVED_NAMES
+
+        for b in bases:
+            if not isinstance(b, cls):
+                bad_names |= vars(b).keys() & constants.RESERVED_NAMES
+        if bad_names:
+            raise ValueError(
+                "Cannot create namespace class with reserved names", sorted(bad_names)
+            )
+        return super().__new__(cls, name, bases, classdict)
+
+    def __iter__(cls):
+        # Walk up the mro, looking for namespace classes. Keep track of attrs we've already seen
+        # and don't re-yield their values
+        seen_attrs = set()
+        for c in cls.__mro__:
+            if isinstance(c, MetaNamespace):
+                for k, v in vars(c).items():
+                    if not util._is_internal(k) and k not in seen_attrs:
+                        seen_attrs.add(k)
+                        yield v