string.Formatter doesn't support empty curly braces "{}"

[RamchandraApte]

BPO	13598
Nosy	@terryjreedy, @vsajip, @ncoghlan, @ericvsmith, @mitsuhiko, @ezio-melotti, @merwok, @florentx, @meadori, @pelson
Files	issue13598.diff: A patch to fix this issue (Version 2) test_string.diff: A patch to test.test_string to test for this bug. issue13598.diff: A patch to fix this issue (Version 3) issue13598.diff: A patch to fix this issue (Version 4) test_string.diff: A patch to test.test_string to test for this bug. (Version 2) pelson_issue13598.diff: An alternative patch to fix the issue (test included). (vn1)

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

Show more details

GitHub fields:

assignee = 'https://github.com/ericvsmith'
closed_at = <Date 2014-04-14.20:45:35.986>
created_at = <Date 2011-12-14.03:59:21.793>
labels = ['type-bug', 'library']
title = 'string.Formatter doesn\'t support empty curly braces "{}"'
updated_at = <Date 2014-05-08.14:46:39.380>
user = 'https://bugs.python.org/RamchandraApte'

bugs.python.org fields:

activity = <Date 2014-05-08.14:46:39.380>
actor = 'aronacher'
assignee = 'eric.smith'
closed = True
closed_date = <Date 2014-04-14.20:45:35.986>
closer = 'eric.smith'
components = ['Library (Lib)']
creation = <Date 2011-12-14.03:59:21.793>
creator = 'Ramchandra Apte'
dependencies = []
files = ['23952', '23955', '24542', '25816', '25817', '27810']
hgrepos = []
issue_num = 13598
keywords = ['patch']
message_count = 30.0
messages = ['149420', '149424', '149426', '149433', '149515', '149523', '149566', '150507', '153397', '153532', '153533', '162207', '162224', '162226', '162254', '162549', '162550', '162551', '162562', '162565', '162668', '174272', '174282', '180281', '180290', '183434', '183453', '216207', '216208', '218114']
nosy_count = 13.0
nosy_names = ['terry.reedy', 'vinay.sajip', 'ncoghlan', 'eric.smith', 'aronacher', 'ezio.melotti', 'eric.araujo', 'flox', 'meador.inge', 'python-dev', 'Ramchandra Apte', 'pelson', 'binkert']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue13598'
versions = ['Python 3.5']

[RamchandraApte]

string.Formatter doesn't support empty curly braces "{}" unlike str.format .

>>> import string
>>> a = string.Formatter()
>>> a.format("{}","test")
Traceback (most recent call last):
  File "<pyshell#2>", line 1, in <module>
    a.format("{}","hello")
  File "/usr/lib/python3.2/string.py", line 180, in format
    return self.vformat(format_string, args, kwargs)
  File "/usr/lib/python3.2/string.py", line 184, in vformat
    result = self._vformat(format_string, args, kwargs, used_args, 2)
  File "/usr/lib/python3.2/string.py", line 206, in _vformat
    obj, arg_used = self.get_field(field_name, args, kwargs)
  File "/usr/lib/python3.2/string.py", line 267, in get_field
    obj = self.get_value(first, args, kwargs)
  File "/usr/lib/python3.2/string.py", line 226, in get_value
    return kwargs[key]
KeyError: ''

[RamchandraApte]

Attached is patch to fix this issue.

[RamchandraApte]

Sorry, the patch has an mistake.
ValueErro should be ValueError.

[RamchandraApte]

Attached is a patch for test.test_string to test for this bug.
Can somebody please comment on my paches or commit my patches.

[RamchandraApte]

Why isn't anybody commiting or commenting on my patches?

[ericvsmith]

This bug is assigned to me. Sometimes it takes a while before a committer has time to review a bug and act on it. I can assure you that I will review this before the next release of Python.

Thank you for the bug report, and especially thanks for the patch!

One thing that will definitely need to be developed before this is committed is one or more tests. Either you can add them, or I will before I commit the fix. There are some existing tests for str.format that can be leveraged for string.Formatter.

[meadori]

On Thu, Dec 15, 2011 at 1:42 AM, maniram maniram <report@bugs.python.org> wrote:

Why isn't anybody commiting or commenting on my patches?

Your patch is much appreciated. Thank you. It takes some time to get
things reviewed. Please read the Dev Guide. In particular, the
"Lifecycle of a Patch"
section: http://docs.python.org/devguide/patch.html.

Also, please quit marking issues as "languishing" unless the issue meets the
qualifications spelled out here:
http://docs.python.org/devguide/languishing.html.

[merwok]

test_string.diff looks good, except that it should probably only test the exception type, not the message (they are not a guaranteed part of the Python language and may change arbitrarily between versions or implementations (e.g. PyPy), so better not to add tests that depend on exact words).

I don’t have anything specific to say about bpo-13598.diff; if it makes the test pass, then it’s good. “if manual == True” should just be replaced by “if manual”.

If you’d like to, you can make one patch with fix + tests that addresses my comments and remove the older diffs.

[ncoghlan]

One potential problem with the simple approach to fixing this is that up until now, string.Formatter has been thread safe. Because all the formatting state was held in local variables and passed around as method arguments, there was no state on the instance object to protect.

Now, this only applies if you start using the new feature, but it should be noted in the documentation and What's New that you need to limit yourself to accessing each formatter instance from a single thread.

It's also enough for me to say "no, not in a maintenance release".

Adding two attributes also seems unnecessary, and the pre-increment looks strange. Why not:

In __init__:
auto_field_count = 0

Then as the auto numbering checking, something like:

    auto_field_count = self.auto_field_count
    if field_name:
        if auto_field_count > 0:
           # Can't switch auto -> manual
        auto_field_count = -1
    elif auto_field_count < 0:
       # Can't switch manual -> auto
    else:
        field_name = str(auto_field_count)
        self.auto_field_count += 1

(Alternatively, I'd ask the question: why do we prevent mixing manual numbering and explicit numbering anyway? It's not like it's ambiguous at all)

[RamchandraApte]

@nick I don't understand why should my patch make Formatter thread-unsafe - the auto_field_count and manual variables are local variables just like the variables in the other functions in Formatter.