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  * The owners of the code would like to keep the changes compatible with Python 2.5.x to avoid having two code bases to maintain, which of course is a bit more involved
    than targeting 2.6 and up.
  * Dealing with a python 2 to python 3 port:
    * The four main ways:
      1. Automatically, fully derive your 3.x code from 2.x
      1. Make code run unmodified on 2.x and 3.x
      1. Maintain two parallel versions
      1. Port to 3.x. Automatically, fully derive your 2.x code from the new 3.x code.
    * The owners of the code prefer methods #1 and #2 over #3 above; we've not yet discussed method 4.
    * Note that Mercurial, the SCM system used by pylint, supports changesets - this could take most of the labor out of method 3

This page describes efforts to port pylint to Python 3.x

Status of the port

Goals and high level overview of tasks

The idea is to add support for Python 3.0 and 3.1, while eliminating Python 2.4 compatibility because that will simplify some of the code.

  • This will require one of the following methods:
    • Converting the three Python 2-compatible packages to a common subset of Python 2 and Python 3
      • We may or may not be able to do this using 2to3; 2to3 may or may not prove too exuberant about moving to a nice, python 3-only syntax in some areas.
    • Creating creating modules that abstract the differences between Python 2 and Python 3 and depending on them instead.
  • About the three packages
    • Those three packages are:
      1. logilab-common
        • This one is probably the place to start, because it appears to contain the test harness we need.
        • The owners of the code believe this will be the easiest part
        • 29274 lines of code initially
      2. logilab-astng
        • 18928 lines of code initially
      3. pylint itself
        • 28415 lines of code initially
    • There appear to be test suites for each of these, which can be invoked using the pytest command - pytest appears to be part of logilab-common, which suggests a bit of
      • mutual dependency to work around.
  • Dealing with a python 2 to python 3 port:
    • The four main ways:
      1. Automatically, fully derive your 3.x code from 2.x
      2. Make code run unmodified on 2.x and 3.x
      3. Maintain two parallel versions
      4. Port to 3.x. Automatically, fully derive your 2.x code from the new 3.x code.
    • The owners of the code prefer methods #1 and #2 over #3 above; we've not yet discussed method 4.
    • Note that Mercurial, the SCM system used by pylint, supports changesets - this could take most of the labor out of method 3

Resources

These are all things related to doing python 2 -> python 3 ports:

  • 2to3
  • Notes about how to do 2 to 3 ports
  • Specific projects' notes on their ports
  • The main issues appear to be:
    • Integer division coerces to a float for non-integral values
      • Use int(x/y) instead of x/y
    • Exceptions are a bit different
      • string exceptions are gone
      •         try:
                  print(1/0)
                except:
                  e = ...
    • str -> bytes, unicode -> str

      • This one's a mess
    • print function instead of statement
      • Use file_.write() instead of print
      • print(var1, var2) happens to work in Python 2, though it doesn't respect some of python 3's options
    • Some things that returned lists, now return iterators. Some things that returned iterators, are gone (or rather, renamed to what formerly returned a list). Example workaround:
      •       try:
                iter = d.iteritems()
              except AttributeError:
                iter = d.items()

PyLint-3k (last edited 2013-12-02 00:10:57 by Charles Merriam)

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