Function Modifier Syntax, by Kevin D. Smith

pep-0318.txt

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+PEP: 318
+Title: Function Modifier Syntax
+Version: $Revision$
+Last-Modified: $Date$
+Author: Kevin D. Smith <Kevin.Smith@theMorgue.org>
+Status: Draft
+Type: Standards Track
+Content-Type: text/plain
+Created: 05-Jun-2003
+Python-Version: 2.4
+Post-History:
+
+
+Abstract
+    
+    The current method for declaring class and static methods
+    is awkward and can lead to code that is difficult to understand.
+    This PEP introduces possible new syntax which will place the
+    translation of instance methods to class/static methods at
+    the same point in the code as the method's declaration. 
+
+
+Motivation
+
+    The current method of translating an instance method into a 
+    class/static method places the actual translation at a different
+    point in the code than the declaration of the method.  The 
+    code below demonstrates this.
+
+        def foo(self):
+            perform method operation
+        foo = classmethod(foo)
+
+    When the method is very short, it is easy to look ahead and see
+    that this is a class method.  However, if the method is more than
+    15 lines or so, the translation into a class method is not 
+    obvious.  A solution to this problem is to move the translation
+    of the method to the same point as the method's declaration.
+
+
+Proposal
+
+    Probably the simplest way to place the function that translates
+    an instance method to a class/static method is illustrated in the
+    code below.
+
+        def classmethod foo(self):
+            perform method operation 
+
+    The code in this example will simply perform the following.
+
+        def foo(self):
+            perform method operation
+        foo = classmethod(foo)
+     
+    This syntax does not introduce any new keywords and is completely
+    backwards compatible with any existing code.  The word between the
+    'def' and the actual name of the method is simply a reference to
+    a callable object that returns a new function reference. 
+    This syntax could also be extended to allow multiple function 
+    modifiers in the form of a space delimited list as follows:
+
+       def protected classmethod foo(self):
+           perform method operation 
+
+    which would be equivalent to the current form:
+
+       def foo(self):
+           perform method operation
+       foo = protected(classmethod(foo))
+
+    While this syntax is simple and easy to read, it does become 
+    cluttered and more obscure if you wish to allow arguments to be 
+    sent to the function modifier.
+
+       def synchronized(lock) classmethod foo(self):
+           perform method operation 
+
+    Various syntaxes have been proposed in comp.lang.python.  The
+    most common are demonstrated below.
+
+        def foo(self) [synchronized(lock), classmethod]:
+            perform method operation
+
+        def foo(self) {'pre': synchronized(lock), 'classmethod': True}:
+            """ Skip Montanaro syntax """
+            perform method operation
+
+        def foo(self) as synchronized(lock), classmethod:
+            """ Gerrit Holl syntax """
+            perform method operation
+
+    I have a strong preference for the last of the three.  The first
+    two use syntax that just seems arbitrary which does not help the
+    user to understand the meaning of it.  The third method is very
+    readable and could probably be interpreted easily by those not
+    familiar with Python.
+
+
+Conclusion
+
+    The current method of translating an instance method to a class
+    or static method is awkward.  A new syntax for applying function
+    modifiers should be implemented (proposed syntax shown below).  
+
+        def foo(self) as synchronized(lock), classmethod:
+            perform method operation
+
+    More generally, 
+
+        def foo(self) as <tuple>:
+            perform method operation
+
+    The proposed syntax is simple, powerful, easy to read, and 
+    therefore preserves those qualities of the Python language.
+
+
+Copyright
+
+    This document has been placed in the public domain.
+
+
+
+Local Variables:
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