IndexError: string index out of range

[fcastilloec]

I'm trying to run autopep8 on my file and this is the output I get:

[file:movieConverter_general.py]
--->  Applying global fix for E265
--->  Applying global fix for W602
--->  161 issue(s) to fix {u'E201': set([32, 113, 234, 123, 71]), u'E203': set([229]), u'E202': set([32, 113, 210, 123, 220]), 'E226': set([149, 150, 152, 156, 159, 160, 164, 171, 201, 202, 204, 208, 209, 210, 213, 214, 218, 219, 220, 95, 96, 97, 228, 229]), u'E211': set([12]), u'E127': set([67, 59, 63]), 'E501': set([129, 135, 140, 143, 19, 34, 171, 175, 189, 196, 76, 82, 84, 88, 89, 228, 229, 106, 238, 239, 116, 118, 249]), 'E265': set([129, 34, 19, 76, 118]), 'E261': set([224, 99, 231, 173, 167]), u'E231': set([135, 148, 149, 150, 151, 152, 153, 154, 155, 156, 158, 159, 160, 161, 162, 163, 164, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 212, 213, 214, 215, 216, 217, 218, 219, 106, 107, 113, 116]), 'E302': set([16, 35, 12, 21, 14]), 'E303': set([194]), 'E305': set([78]), u'E129': set([140])}
Traceback (most recent call last):
  File "/usr/local/bin/autopep8", line 11, in <module>
    sys.exit(main())
  File "/usr/local/lib/python2.7/dist-packages/autopep8.py", line 3811, in main
    fix_multiple_files(args.files, args, sys.stdout)
  File "/usr/local/lib/python2.7/dist-packages/autopep8.py", line 3723, in fix_multiple_files
    _fix_file((name, options, output))
  File "/usr/local/lib/python2.7/dist-packages/autopep8.py", line 3704, in _fix_file
    fix_file(*parameters)
  File "/usr/local/lib/python2.7/dist-packages/autopep8.py", line 3104, in fix_file
    fixed_source = fix_lines(fixed_source, options, filename=filename)
  File "/usr/local/lib/python2.7/dist-packages/autopep8.py", line 3084, in fix_lines
    fixed_source = fix.fix()
  File "/usr/local/lib/python2.7/dist-packages/autopep8.py", line 564, in fix
    aggressive=self.options.aggressive))
  File "/usr/local/lib/python2.7/dist-packages/autopep8.py", line 507, in _fix_source
    modified_lines = fix(result)
  File "/usr/local/lib/python2.7/dist-packages/autopep8.py", line 872, in fix_long_line_physically
    original=target)
  File "/usr/local/lib/python2.7/dist-packages/autopep8.py", line 903, in fix_long_line
    verbose=self.options.verbose)
  File "/usr/local/lib/python2.7/dist-packages/autopep8.py", line 1166, in get_fixed_long_line
    key=lambda x: line_shortening_rank(
  File "/usr/local/lib/python2.7/dist-packages/autopep8.py", line 1170, in <lambda>
    experimental=experimental))
  File "/usr/local/lib/python2.7/dist-packages/autopep8.py", line 3465, in line_shortening_rank
    lines[0].rstrip()[-1] not in '([{'
IndexError: string index out of range

I've tried to look everywhere what's going on, but I haven't found any answers.
Here's the version of my packages:
autopep8 1.3.2 (pycodestyle: 2.3.1)
pep8 1.7.0

I'm using Ubuntu 16.04, and as the versions show, I install the packages using pip

[christarazi]

I managed to fix this issue. Somewhat of a stopgap solution, because I did not look too deep into why this was occurring (also because I am unsure if rank should be returned in its current state). Maybe the maintainers will have a better idea on how to avoid this. The patch is below (from git format-patch):

From 7f25de9b5eae80d8ce7cb5df8af233e17bb60775 Mon Sep 17 00:00:00 2001
From: Chris Tarazi <tarazichris@gmail.com>
Date: Mon, 18 Sep 2017 11:55:23 -0700
Subject: [PATCH 1/1] Fix issue #346: avoid IndexError on empty line

---
 autopep8.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/autopep8.py b/autopep8.py
index 918af2d..f79ad71 100755
--- a/autopep8.py
+++ b/autopep8.py
@@ -3520,6 +3520,10 @@ def line_shortening_rank(candidate, indent_word, max_line_length,
     rank = 0
     lines = candidate.rstrip().split('\n')
 
+    # Avoid IndexError -- first line may be empty.
+    if not lines[0].rstrip():
+        return rank
+
     offset = 0
     if (
         not lines[0].lstrip().startswith('#') and
-- 
2.14.1

[myint]

A code example would be helpful us. Thanks!

[pikacic]

I have the same problem with this chunk of code:

def something:
    pass

# a quick brown fox jumps over the lazy dog, again, again, again, again, again..
something_else = 123

The comment is the line that triggers the problem.

[christarazi]

Can confirm @pikacic example triggers the problem. Seems like a very long comment that comes after a line that requires indentation is what causes it.

[myint]

I can't reproduce the IndexError with @pikacic's example. Though, there is indeed something wrong there that could be related. The comment is getting mangled.

$ ./autopep8.py foo.py  -aaavd
[file:foo.py]
--->  Applying global fix for E265
--->  Applying global fix for W602
--->  2 issue(s) to fix {'E501': {4}, 'E305': {5}}
--->  0 issue(s) to fix {}

--- original/foo.py
+++ fixed/foo.py
@@ -1,5 +1,8 @@
 def something():
     pass

-# a quick brown fox jumps over the lazy dog, again, again, again, again, again..
+
+#  # a quick brown fox jumps over the lazy dog, again, again, again,
+
+# again, again..
 something_else = 123

[hhatto]

@fcastilloec
autopep8 version 1.3.3 has been released.
Can you try it as it has been fixed in the latest version?

[fcastilloec]

@hhatto I just updated to v1.3.3 and I don't see the error anymore! Thanks so much!