fix_idioms.py generates bad code

[hawking]

BPO	3563
Nosy	@terryjreedy, @benjaminp, @mitsuhiko
Files	indentation_test.diff fix_idioms.patch: Patch that should fix this bug and test that this bug has been fixed.

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/benjaminp'
closed_at = <Date 2009-10-07.21:26:21.009>
created_at = <Date 2008-08-16.07:03:07.059>
labels = ['expert-2to3']
title = 'fix_idioms.py generates bad code'
updated_at = <Date 2009-10-07.21:26:21.007>
user = 'https://bugs.python.org/hawking'

bugs.python.org fields:

activity = <Date 2009-10-07.21:26:21.007>
actor = 'benjamin.peterson'
assignee = 'benjamin.peterson'
closed = True
closed_date = <Date 2009-10-07.21:26:21.009>
closer = 'benjamin.peterson'
components = ['2to3 (2.x to 3.x conversion tool)']
creation = <Date 2008-08-16.07:03:07.059>
creator = 'hawking'
dependencies = []
files = ['11124', '15062']
hgrepos = []
issue_num = 3563
keywords = ['patch']
message_count = 7.0
messages = ['71199', '71217', '71777', '77298', '93672', '93673', '93725']
nosy_count = 6.0
nosy_names = ['collinwinter', 'terry.reedy', 'hawking', 'benjamin.peterson', 'aronacher', 'joe.amenta']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue3563'
versions = []

[hawking]

fix_idioms.py generates bad code for conversions in try/except blocks.
Example:
s=(1, 2, 3)
try:
t = list(s)
t.sort()
except TypeError:
pass

fix_idioms.py generates this diff:
--- test.py (original)
+++ test.py (refactored)
@@ -7,8 +7,7 @@
 
 s=(1, 2, 3)
 try:
-    t = list(s)
-    t.sort()
-except TypeError:
+    t = sorted(s)
+    except TypeError:
     pass
 
except TypeError is indented wrongly.

[benjaminp]

It's due to these lines in fix_idioms:

if next_stmt:
     next_stmt[0].set_prefix(sort_stmt.get_prefix())

I'm not sure what the correct way to deal with this is. Anyway I'm
attaching a test case.

[terryjreedy]

Why is the statement, whatever it is, even being touched?
Would not the same problem arise with any following outdented line?

IOW, why not delete that pair of lines from fix_idioms.py?
Does that break anything else in test_fixers?

[mitsuhiko]

I would drop the prefix in that case or attach it to the sorted() call.

So from this code:

    x = foo()
    # perform sorting
    x.sort()

to

    # perform sorting
    x = sorted(foo())

Makes more sense than sticking it after the sorted() call like it
happens currently. This should also fix the problem with outdented
statements such as except/finally.

[joeamenta]

Attached a patch that implements more thoroughly what appears to be the
intended behavior.

[joeamenta]

Missed a paren in the last one... re-uploading it.

[benjaminp]

Thanks very much for the patch; Committed in r75278.