Raymond Hettinger's latest updates.

pep-0279.txt

@@ -45,7 +45,7 @@ Rationale
     2. Provide a generator alternative to list comprehensions [3]
        making generator creation as convenient as list creation.
 
-    3. Extend the syntax of the 'yield' keyword to enable two way
+    3. Extend the syntax of the 'yield' keyword to enable generator
        parameter passing.  The resulting increase in power simplifies
        the creation of consumer streams which have a complex execution
        state and/or variable state.
@@ -57,7 +57,8 @@ Rationale
     All of the suggestions are designed to take advantage of the
     existing implementation and require little additional effort to
     incorporate.  Each is backward compatible and requires no new
-    keywords.
+    keywords.  These generator tools go into Python 2.3 when
+    generators become final and are not imported from __future__.
 
 
 Specification for new built-ins:
@@ -149,33 +150,20 @@ Specification for new built-ins:
 Specification for Generator Comprehensions:
 
     If a list comprehension starts with a 'yield' keyword, then
-    express the remainder of the statement as generator.  For example:
+    express the comprehension with a generator.  For example:
 
-        g = [yield (len(line),line) for line in file.readline() if len(line)>5]
-        print g.next()
-        print g.next()
+        g = [yield (len(line),line)  for line in file  if len(line)>5]
 
     This would be implemented as if it had been written:
 
-        def __temp_gen():
-            for line in file.readline():
+        class __Temp:
+            def __iter__(self):
+                for line in file:
                     if len(line) > 5:
                         yield (len(line), line)
-        g = __temp_gen()
-        print g.next()
-        print g.next()
+        g = __Temp()
 
-    Note A: There is a difference in the above implementation as
-    compared to list comprehensions.  For a generator comprehension,
-    the variables are created in a separate scope while list
-    comprehensions use the enclosing scope.  If this PEP is accepted,
-    the parser should generate byte code that eliminates this
-    difference by passing the line variable in the enclosing scope and
-    using that same variable passed by reference inside the generator.
-    This will make the behavior of generator comprehension identical
-    to that of list comprehensions.
-
-    Note B: There is some debate about whether the enclosing brackets
+    Note A: There is some debate about whether the enclosing brackets
     should be part of the syntax for generator comprehensions.  On the
     plus side, it neatly parallels list comprehensions and would be
     immediately recognizable as a similar form with similar internal
@@ -190,7 +178,7 @@ Specification for Generator Comprehensions:
     in fact helpful.
 
 
-Specification for two-way Generator Parameter Passing:
+Specification for Generator Parameter Passing:
 
     1. Allow 'yield' to assign a value as in:
 
@@ -209,7 +197,7 @@ Specification for two-way Generator Parameter Passing:
     The control flow is unchanged by this proposal.  The only change
     is that a value can be sent into the generator.  By analogy,
     consider the quality improvement from GOSUB (which had no argument
-    passing mechanism) to modern procedure calls (which pass in
+    passing mechanism) to modern procedure calls (which can pass in
     arguments and return values).
 
     Most of the underlying machinery is already in place, only the
@@ -234,7 +222,7 @@ Specification for two-way Generator Parameter Passing:
     threading module with its attendant mutexes, semaphores, and data
     queues.  A class-based approach competes well when there are no
     complex execution states or variable states.  When the complexity
-    increases, generators with two-way communication are much simpler
+    increases, generators with parameter passing are much simpler
     because they automatically save state (unlike classes which must
     explicitly save the variable and execution state in instance
     variables).
@@ -281,6 +269,15 @@ Specification for two-way Generator Parameter Passing:
     more thumbnails on it.
 
 
+    Example of a Producer and Consumer Used Together in a Pipelike Fashion
+
+        'Analogy to:  source | upper | sink'
+        sink = sinkgen()
+        sink.next()
+        for word in source():
+            sink.next( word.upper() )
+
+
 Specification for Generator Exception Passing:
 
     Add a .throw(exception) method to the resulting generator as in:
@@ -311,6 +308,13 @@ Specification for Generator Exception Passing:
     putting the exception in another location.  The word throw is
     already associated with exceptions in other languages.
 
+    Note B: The throw syntax should exactly match raise's syntax including:
+            raise string                    g.throw(string)
+            raise string, data              g.throw(string,data)
+            raise class, instance           g.throw(class,instance)
+            raise instance                  g.throw(instance)
+            raise                           g.throw()
+
 
 References
 
@@ -342,7 +346,7 @@ References
         http://groups.google.com/groups?hl=en&th=df8b5e7709957eb7
 
     [5] Dr. David Mertz's draft column for Charming Python.
-        href="http://gnosis.cx/publish/programming/charming_python_b5.txt
+        http://gnosis.cx/publish/programming/charming_python_b5.txt
 
 
 Copyright
@@ -356,3 +360,5 @@ mode: indented-text
 indent-tabs-mode: nil
 fill-column: 70
 End:
+
+