[Assorted-commits] SF.net SVN: assorted:[912] sandbox/trunk/src/py/with_decorator.py

[<yan...@us...>]

Revision: 912
          http://assorted.svn.sourceforge.net/assorted/?rev=912&view=rev
Author:   yangzhang
Date:     2008-07-30 02:08:37 +0000 (Wed, 30 Jul 2008)

Log Message:
-----------
added demo that with cannot be implemented in python 2.4

Added Paths:
-----------
    sandbox/trunk/src/py/with_decorator.py

Added: sandbox/trunk/src/py/with_decorator.py
===================================================================
--- sandbox/trunk/src/py/with_decorator.py	                        (rev 0)
+++ sandbox/trunk/src/py/with_decorator.py	2008-07-30 02:08:37 UTC (rev 912)
@@ -0,0 +1,45 @@
+# Can we implement the with statement using decorators? Not really....
+
+class ctxmgr(object): pass # not used
+
+def With(ctx):
+    def wrapper(func):
+        if type(ctx) == ctxmgr:
+            rsrc = ctx.enter()
+            if func.func_code.co_argcount == 0: result = func()
+            else: result = func(rsrc)
+            ctx.exit()
+        elif type(ctx).__name__ == 'generator':
+            rsrc = ctx.next()
+            if func.func_code.co_argcount == 0: result = func()
+            else: result = func(rsrc)
+        else: assert False, type(ctx)
+        return result
+    return wrapper
+
+# some context managers
+
+def closing(rsrc):
+    try: yield rsrc
+    finally: print 'CLOSIN'; rsrc.close()
+
+def locking(path):
+    @With(closing(file(path, 'w')))
+    def foo(f):
+        flock(f, LOCK_EX)
+        # here is where we fail!  we'd need to yield two levels up the
+        # stack!
+        try: yield
+        finally: flock(f, LOCK_UN)
+    return foo
+
+# demos
+
+@With(closing(file('/tmp/hello', 'w')))
+def foo(f): print 'WRITING'; f.write('hello!')
+
+@With(locking('/tmp/mylock'))
+def foo():
+    print 'locked'
+    return raw_input()
+print foo


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