Hello,
after proposing this here (albeit deep in the PEP 340 thread) and
getting a somewhat affirmatory response from Guido, I have written
something that could become a PEP if sufficiently hatched...
---------------------------
PEP: XXX
Title: Unifying try-except and try-finally
Version: $Revision: $
Last-Modified: $Date: $
Author: Reinhold Birkenfeld <[EMAIL PROTECTED]>
Status: Draft
Type: Standards Track
Content-Type: text/plain
Created: 04-May-2005
Post-History:
Abstract
This PEP proposes a change in the syntax and semantics of try
statements to allow combined try-except-finally blocks. This
means in short that it would be valid to write
try:
<do something>
except Exception:
<handle the error>
finally:
<cleanup>
Rationale/Proposal
There are many use cases for the try-except statement and
for the try-finally statement per se; however, often one needs
to catch exceptions and execute some cleanup code afterwards.
It is slightly annoying and not very intelligible that
one has to write
f = None
try:
try:
f = open(filename)
text = f.read()
except IOError:
print 'An error occured'
finally:
if f:
f.close()
So it is proposed that a construction like this
try:
<suite 1>
except Ex1:
<suite 2>
<more except: clauses>
else:
<suite 3>
finally:
<suite 4>
be exactly the same as the legacy
try:
try:
<suite 1>
except Ex1:
<suite 2>
<more except: clauses>
else:
<suite 3>
finally:
<suite 4>
This is backwards compatible, and every try statement that is
legal today would continue to work.
Changes to the grammar
The grammar for the try statement, which is currently
try_stmt: ('try' ':' suite (except_clause ':' suite)+
['else' ':' suite] | 'try' ':' suite 'finally' ':' suite)
would have to become
try_stmt: ('try' ':' suite (except_clause ':' suite)+
['else' ':' suite] ['finally' ':' suite] |
'try' ':' suite (except_clause ':' suite)*
['else' ':' suite] 'finally' ':' suite)
Implementation
As the PEP author currently does not have sufficient knowledge
of the CPython implementation, he is unfortunately not able
to deliver one.
References
None yet.
Copyright
This document has been placed in the public domain.
-----------------------
Reinhold
--
Mail address is perfectly valid!
_______________________________________________
Python-Dev mailing list
Python-Dev@python.org
http://mail.python.org/mailman/listinfo/python-dev
Unsubscribe:
http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
