View source for GEPS 031: Python 3 support

Gramps was written with python 2. Slowly the default python is becoming python 3. Gramps 4.0 will require python 2.7+. Ideally we also support python 3. Then in 2014-15 we can drop python 2.7 support. For convenience, we aim for python 3.2+


== Guideline ==
No python 2.7 only constructs should be present, and no python 3.2 only constructs should be present.

== Can I work with both pythons?==
On the same family tree, normally not! For python3, bsddb is no longer a core package. You need to install python3-bsddb, and that will normally be a more recent version than what is present in python 2.7. 

So, once you open a family tree with python3, you will not be allowed to open it with python 2.7. The only way to open it with python 2.7 is using the bsddb3 option of Gramps, and installing from source the bsddb3 package for python 2.7 that is as current as the one given in python3

== Tips ==
# If you work with python3, edit the ~/.subversion/config files, and add the section
 global-ignores = __pycache__
# Give a family tree a name that contains 32 if you use python 3, and 27 if you use python 2. Once you open a python 2 family tree, the database is upgrade and you canot open it again in python 2 (you could export to xml and import in python 2 though)

== How? ==

See patchset in [http://www.gramps-project.org/bugs/view.php?id=2620].

Main attention points:

* we should not use unicode anymore. Instead, import from ''gramps.gen.constfunc'' the cuni or friends functions to convert to unicode
* we should not compare to basestring or unicode type. Instead use UNITYPE and STRTYPE from ''gramps.gen.constfunc''
* in python 3 many functions became iterators. Remove the old 2.7 names and replace with the 3.2 names as much as possible. Only when performance is really an issue, use an if construct on python version so that python 2.7 also uses an iterator.
* you will see a lot of list(map ...) or list(range...) after conversion. Only remove this if you studied the code and know it will work in python 2 and 3
* If special unicode symbols are needed, then use ''from __future__ import unicode_literals'' '''and''' ''# -*- coding: utf-8 -*-'' and adapt the 2.7 code to have it working with this. 
* to test on python version, use ''if sys.version_info[0] < 3:'' for consistency with the other patches.

== Requirements ==
=== Ubuntu 12.10 ===
Python 3.2.3 ships with Ubuntu 12.10. To run Gramps, you will also need the packages:
# python3-gi: gobject introspection
# python3-gi-cairo: cairo gobject instrospection
# python3-cairo : This is needed to have ''import cairo'' work
# python3-bsddb3: This is needed to have ''import bsddb3'' work

== Related Gramps Bugs ==
* #{{bug|2620}}: GEPS 031: Python 3 support - 3.2

See also [[GEPS_032:_Python_3_support/Python_3_Deprecated|Python 3 Deprecated]]
[[Category:GEPS|P]]