117 lines
2.7 KiB
Plaintext
117 lines
2.7 KiB
Plaintext
|
PEP: 341
|
|||
|
Title: Unifying try-except and try-finally
|
|||
|
Version: $Revision$
|
|||
|
Last-Modified: $Date$
|
|||
|
Author: Reinhold Birkenfeld <reinhold-birkenfeld-nospam@wolke7.net>
|
|||
|
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.
|
|||
|
|
|||
|
However, according to Guido, it should be a piece of cake to
|
|||
|
implement[1] -- at least for a core hacker.
|
|||
|
|
|||
|
|
|||
|
References
|
|||
|
|
|||
|
[1] http://mail.python.org/pipermail/python-dev/2005-May/053319.html
|
|||
|
|
|||
|
|
|||
|
Copyright
|
|||
|
|
|||
|
This document has been placed in the public domain.
|
|||
|
|
|||
|
|
|||
|
|
|||
|
Local Variables:
|
|||
|
mode: indented-text
|
|||
|
indent-tabs-mode: nil
|
|||
|
sentence-end-double-space: t
|
|||
|
fill-column: 70
|
|||
|
End:
|