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| This is a status page for keeping track of what needs to be done to make progress on Mercurial on Python 3. Our current aim is to support Python 3.5. | This is a status page for keeping track of what needs to be done to make progress on Mercurial on Python 3. Our current aim is to support Python 3.5+. |
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| == What Works == `hg version`, `hg debuginstall`, `hg init`, `hg files`, `hg manifest`, `hg log`, `hg diff`, `hg export`, `hg status`, `hg summary`, `hg config`, `hg identify`, `hg update`, `hg commit`, `hg branches`, `hg bookmarks` works on Python 3 without using any out of core extensions. These won't work for you if you have out of core extensions enabled. There are certain things which don't work yet with these commands like revset, templates. |
<<TableOfContents>> |
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| We have some handful of tests passing on Python 3. You can have a look at them in [[https://www.mercurial-scm.org/repo/hg-committed/file/tip/contrib/python3-whitelist|python3-whitelist]] | == Status == |
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| == Contributing == | We have been testing by installing default mercurial on our system using Python 3. Most of the things work correctly. Things which don't work can be found at BetaBugs section below. |
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| We will be happy to review patches and speed up the work related to Python 3. Before you start there are few things related to current porting and how things work currently. Most of our efforts are to make sure have Python 2 compatibility intact while making Python 3 run. | We are planning to mark hg 5.0 which is scheduled for May 1 as Python 3 beta release. |
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| * We have a source transformer which does following things on Python 3. 1. It adds b'' in front of string starting with "'" or '"' and not having any u'', r'' or b'' in front. 2. Adds this line `from mercurial.pycompat import delattr, getattr, hasattr, setattr, xrange, open` on every python file. 3. Converts every occurrence of `iteritems` to `items` on Python 3. 4. Converts argument of *attr and encode, decode to unicodes by adding u''. 5. The transformer currently works on `mercurial/, hgext/ and hgext3rd/`. 6. The transformer code lies [[https://www.mercurial-scm.org/repo/hg/file/295625f1296b/mercurial/__init__.py#l124|here]] and you can also use transformer on your .py files by adding them in the transformer. |
If you are an extension author and want to port the extension, [[https://www.mercurial-scm.org/repo/hg-committed/file/tip/mercurial/pycompat.py||pycompat.py]] contains most of our compatibility hacks. If you need help or guidance, you can message on IRC or devel mailing list. We will be happy to help you. |
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| * Due to everything is unicodes by default in Python 3, and we need to rely on bytes, we have [[https://www.mercurial-scm.org/repo/hg/file/tip/mercurial/pycompat.py|pycompat.py]] which contains hacks related to various functions of `os` module on Python. | |
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| * We also have `encoding.environ` which helps us using a bytes version of `os.environ` on both Python 2 and 3. | == Things need to be investigated == |
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| * We are also adding r'' at some places to make it a raw string. | * Windows encoding changes https://docs.python.org/3/whatsnew/3.6.html#pep-529-change-windows-filesystem-encoding-to-utf-8 * Lazy importer performance overhead. Our custom importer on Python 2 always returns a stub module during ``import``. Python 3's does I/O to verify the module exists then returns a lazy module that is loaded when first accessed. In addition to behavior differences, the I/O may contribute sufficient performance overhead to constitute a problem. * A mechanism for extensions to advertise that they are Python 3 compatible. Nearly every extension will break in Python 3. We may want a mechanism that requires extensions to self-declare that they are Python 3 compatible - possibly via special syntax in their source code or the presence of a well-named variable. It might have to be at the source level because Python 3 would need to evaluate code in order to obtain the value of a module-level variable. |
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| * There are currently two tests which are based on Python 3 compatibility and few checks in our linter [[https://www.mercurial-scm.org/repo/hg/file/tip/tests/test-check-code.t|test-check-code.t]] to make sure new patches include things from `pycompat.py`. | |
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| 1. [[https://www.mercurial-scm.org/repo/hg/file/tip/tests/test-check-py3-compat.t|test-check-py3-compat.t]] : This test was used initially to fix a lot of things, not very much helpful now. 2. [[https://www.mercurial-scm.org/repo/hg/file/tip/tests/test-py3-commands.t|test-py3-commands.t]]: This test lists commands which actually works on Python 3. If you want an updated list anytime, the test is the best place to look for. |
== Beta bugs == |
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| * Encoding issues are generally uncovered by our tests (as everything was byte string on Python 2.) | Following are things which don't work right now: |
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| == How to start == | * ~1% of tests fail * phabricator extension * curses interface * out of core extensions |
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| * You can always set up a virtual environment and run Mercurial in it, but we have a easier way around. 1. Clone the [[https://www.mercurial-scm.org/repo/hg|main repo]] or [[https://www.mercurial-scm.org/repo/hg-committed/|committed-repo]] and say it's in folder name `hgrepo`. 2. Have Python 3.5 installed and say you have it in variable `python3.5`. 3. Run `hgrepo$ python3.5 hg version`. That must work, if not check that you should not have out of tree extensions enabled. 4. Now you can run any hg command this way and test if it's working or not. |
If you find anything apart from this not working, definitely go ahead and edit this page and we will fix it. |
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| The practice we follow now is run commands which are not yet fixed and try to fix the exceptions raised. So our current approach is exception based. |
Note:
This page is primarily intended for developers of Mercurial.
Python 3
This is a status page for keeping track of what needs to be done to make progress on Mercurial on Python 3. Our current aim is to support Python 3.5+.
1. Status
We have been testing by installing default mercurial on our system using Python 3. Most of the things work correctly. Things which don't work can be found at BetaBugs section below.
We are planning to mark hg 5.0 which is scheduled for May 1 as Python 3 beta release.
If you are an extension author and want to port the extension, https://www.mercurial-scm.org/repo/hg-committed/file/tip/mercurial/pycompat.py contains most of our compatibility hacks. If you need help or guidance, you can message on IRC or devel mailing list. We will be happy to help you.
2. Things need to be investigated
- Windows encoding changes
https://docs.python.org/3/whatsnew/3.6.html#pep-529-change-windows-filesystem-encoding-to-utf-8
Lazy importer performance overhead. Our custom importer on Python 2 always returns a stub module during import. Python 3's does I/O to verify the module exists then returns a lazy module that is loaded when first accessed. In addition to behavior differences, the I/O may contribute sufficient performance overhead to constitute a problem.
- A mechanism for extensions to advertise that they are Python 3 compatible. Nearly every extension will break in Python 3. We may want a mechanism that requires extensions to self-declare that they are Python 3 compatible - possibly via special syntax in their source code or the presence of a well-named variable. It might have to be at the source level because Python 3 would need to evaluate code in order to obtain the value of a module-level variable.
3. Beta bugs
Following are things which don't work right now:
- ~1% of tests fail
- phabricator extension
- curses interface
- out of core extensions
If you find anything apart from this not working, definitely go ahead and edit this page and we will fix it.