| msg284249 - (view) |
Author: Jim Fasarakis-Hilliard (Jim Fasarakis-Hilliard) * |
Date: 2016-12-29 11:56 |
| In short: >>> f"\{10}" yields: "\\{10" This is reproducible only when `\` precedes the opening bracket, that is: >>> f"\ {10}" results in: "\\ 10" |
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| msg284256 - (view) |
Author: Eric V. Smith (eric.smith) *  |
Date: 2016-12-29 12:45 |
| I'm not sure this counts as an error. The backslash means to treat the next character literally, which this does. And since \{ is not a valid escape sequence, it keeps both characters, exactly like: >>> '\c' '\\c' Furthermore, since unknown escape sequences are deprecated, this usage is going to be an error in the future. You can see this now with -Werror: $ python.exe -Werror Python 3.6.0b1+ (3.6:87de1f12c41c+, Sep 16 2016, 07:05:57) [MSC v.1900 64 bit (AMD64)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>> f'\{10}' DeprecationWarning: invalid escape sequence '\{' >>> '\c' DeprecationWarning: invalid escape sequence '\c' >>> Since this works as I expect it to now, and since it will become an error in the future, I don't think any change is warranted. |
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| msg284257 - (view) |
Author: Eric V. Smith (eric.smith) * |
Date: 2016-12-29 12:48 |
| But I admit that dropping the trailing } seems odd. I think this particular usage should be an error: no bare } allowed, similar to: >>> f'10}' File "", line 1 SyntaxError: f-string: single '}' is not allowed |
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| msg284258 - (view) |
Author: Jim Fasarakis-Hilliard (Jim Fasarakis-Hilliard) * |
Date: 2016-12-29 12:57 |
| I see, the original "complaint" about this behavior on stack overflow was made due to the discrepancy between the f-string the the format "equivalent": '\{}'.format(10)'. |
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| msg284259 - (view) |
Author: Eric V. Smith (eric.smith) * |
Date: 2016-12-29 13:02 |
| Do you have a link to the SO question? |
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| msg284260 - (view) |
Author: Jim Fasarakis-Hilliard (Jim Fasarakis-Hilliard) * |
Date: 2016-12-29 13:07 |
| Yes, should've attached in my previous message. See http://stackoverflow.com/questions/41330097/why-does-the-symbol-remain-when-f-10-is-evaluated-in-python-3-6 |
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| msg284261 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2016-12-29 13:37 |
| The problem is not that the trailing } is dropped, but that the starting { starts an f-string expression. >>> f'\{2*5}' '\\{10' I expected either '\\10' as in '\{}'.format(2*5), or at least '\\{2*5}'. There is other f-string parsing error: >>> f'\\N{2*5}' '\\N{2*5}' I expected '\\N10'. '\\N' doesn't start a unicode name escape. This is a legitimate expression. |
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| msg284262 - (view) |
Author: Eric V. Smith (eric.smith) * |
Date: 2016-12-29 13:40 |
| Yes: >>> f'\{2*5}' '\\{10' I agree '\\10' would make sense. |
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| msg284266 - (view) |
Author: Eric V. Smith (eric.smith) * |
Date: 2016-12-29 14:42 |
| This problem was no doubt introduced after 3.6a1 when I changed the parsing to disallow backslashes inside {}. |
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| msg284271 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2016-12-29 15:10 |
| Proposed patch fixes parsing backslashes in f-strings. P.S. Definitely we should find other name for this term. I hate misleading "f-string". |
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| msg284558 - (view) |
Author: STINNER Victor (vstinner) * |
Date: 2017-01-03 13:12 |
| The PEP 498 should be updated to define the expected behaviour of f'\{5}': https://www.python.org/dev/peps/pep-0498/#escape-sequences + self.assertEqual(f'\{6*7}', '\\42') + self.assertEqual(f'\\{6*7}', '\\42') + self.assertEqual(fr'\{6*7}', '\\42') + + AMPERSAND = 123 + self.assertEqual(f'\N{AMPERSAND}', '&') + self.assertEqual(f'\\N{AMPERSAND}', '\\N123') + self.assertEqual(fr'\N{AMPERSAND}', '\\N123') + self.assertEqual(f'\\\N{AMPERSAND}', '\\&') I'm not sure that I like this behaviour. f'\\N{AMPERSAND}': reading a local variable looks like a typo or a security vulnerability, rather than a nice feature. IMHO if you want an anti-slash (\) in the output string, it *must* be written "\\" since we *do* interpret other escape sequences: * f'\n' returns '\n', the newline character U+000A * f'\N{Snowman}' returns the nice snowman character U+2603 (☃) * etc. What is the issue with having to write "\\{10}" to get "\\10" string? It's less error prone. |
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| msg284578 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2017-01-03 15:31 |
| > f'\\N{AMPERSAND}': reading a local variable looks like a typo or a security vulnerability, rather than a nice feature. This can look as a typo, but how would you write this if this is not a typo? f'\\N{AMPERSAND}' is legitimate syntax, and it would be weird to interpret this expression in any other way than as '\\' + 'N' + format(AMPERSAND). > What is the issue with having to write "\\{10}" to get "\\10" string? It's less error prone. There is no issue with f'\\{10}'. There is an issue with f'\{10}'. |
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| msg284579 - (view) |
Author: STINNER Victor (vstinner) * |
Date: 2017-01-03 15:33 |
| > There is no issue with f'\\{10}'. There is an issue with f'\{10}'. Hum, I'm not sure that my previous comment is explicit: I suggest to raise a syntax error on f'\{10}' (or emit a warning, and raise an error in 3.7 if you insist ;-)). |
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| msg284580 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2017-01-03 15:59 |
| Updated patch adds a warning. |
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| msg285949 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2017-01-21 11:22 |
| Ping. |
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| msg288511 - (view) |
Author: Jim Fasarakis-Hilliard (Jim Fasarakis-Hilliard) * |
Date: 2017-02-24 09:33 |
| Serhiy, since review activity has dropped on b.p.o now that the move to github was made, would you like to make this into a pull request to get it reviewed and merged faster? |
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| msg288979 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2017-03-04 15:15 |
| I am not experienced with git and am waiting until new workflow be described in the devguide. |
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| msg289645 - (view) |
Author: Eric V. Smith (eric.smith) * |
Date: 2017-03-15 07:19 |
| Serhiy: I plan to find time in the next week or so to look at this. Sorry for the delay. Plus, the new workflow isn't helping me out: I need to get up to speed on it. |
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| msg289689 - (view) |
Author: Ryan Gonzalez (refi64) * |
Date: 2017-03-15 19:07 |
| Serhiy: if you want, you can give me your email and I'll submit a PR for you. If you want to do it yourself, just: Download hub: https://hub.github.com/ git clone python/cpython cpython-git cd cpython-git git fork curl https://raw.githubusercontent.com/mozilla/moz-git-tools/master/hg-patch-to-git-patch > hg-patch-to-git-patch curl https://bugs.python.org/file46127/fstring_backslash_2.patch | python2 hg-patch-to-git-patch > fstring.patch git checkout -b fstring-fix git apply fstring.patch git commit -am 'bpo-29104: Commit message here' git push -u MY_GITHUB_USERNAME fstring-fix git pull-request |
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| msg289690 - (view) |
Author: Jim Fasarakis-Hilliard (Jim Fasarakis-Hilliard) * |
Date: 2017-03-15 19:09 |
| A PR has been submitted, Ryan. See https://github.com/python/cpython/pull/490 |
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| msg289694 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2017-03-15 20:42 |
| Thank you Ryan. I already created a PR, but I think your recipe can be helpful for me in future. |
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| msg290733 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2017-03-28 15:43 |
| Ping again. |
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| msg293604 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2017-05-13 08:34 |
| Eric? |
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| msg293608 - (view) |
Author: Eric V. Smith (eric.smith) * |
Date: 2017-05-13 09:08 |
| This is on my list of things to review at PyCon, when I should finally have some free time. |
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| msg294458 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2017-05-25 10:33 |
| New changeset 0cd7a3f196cf34d9bb0a52e61327f7fe289d9750 by Serhiy Storchaka in branch 'master': bpo-29104: Fixed parsing backslashes in f-strings. (#490) https://github.com/python/cpython/commit/0cd7a3f196cf34d9bb0a52e61327f7fe289d9750 |
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| msg294469 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2017-05-25 11:18 |
| New changeset 89a310264000a613b7f6abd5916946aef09ae7d2 by Serhiy Storchaka in branch '3.6': [3.6] bpo-29104: Fixed parsing backslashes in f-strings. (GH-490) (#1812) https://github.com/python/cpython/commit/89a310264000a613b7f6abd5916946aef09ae7d2 |
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