Migrate Django applications running on Python 2.7 to Python 3.5

What is this?

This document is a note from investigating the cost of migrating Django applications running on Python 2.7 to Python 3.5.

2to3 Change xrange and [keys () ,values () Change, ʻitems ()](http://diveintopython3-ja.rdy.jp/porting-code-to-python-3-with-2to3.html#dict) with 2to3`.

Since it is possible to specify conversions that are not applied with -x, the following conversions are excluded.

• future --from __future__ import unicode_literals can be left, so it is excluded to reduce diff.
• print --I've been thorough in using the print function and excluded the print statement as it shouldn't exist
• callable --callable is not available only for Python 3.0 / 3.1 and is not required as it is expected to migrate to Python 3.5.x.

Overwrite the original file with the -w option to perform the conversion.

$ 2to3 -x future -x print -x callable -w .

Libraries that needed to be updated

python-memcached

• https://pypi.python.org/pypi/python-memcached

However, I think the behavior when putting the binary in Memcached is suspicious.

tweepy

• https://pypi.python.org/pypi/tweepy

google-api-python-client

• https://github.com/google/google-api-python-client

Django Requires update to 1.8.x.

File "/home/csakatoku/.pyenv/versions/3.5.0/lib/python3.5/site-packages/django/utils/html_parser.py", line 12, in <module>
    HTMLParseError = _html_parser.HTMLParseError
AttributeError: module 'html.parser' has no attribute 'HTMLParseError'

Libraries that need to be transferred

dnspython You need to change to dnspython3 released under a different package name. If you specify dnspython3 when installing with pip, it's OK and you don't need to change the code.

MySQL-python

• https://pypi.python.org/pypi/MySQL-python --No problem if you use mysqlclient instead of MySQL-python.

Library that doesn't work

bitly-api Does not work with ʻImport Error`. However, it seems that it has been fixed in master.

>>> import bitly_api
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/csakatoku/.pyenv/versions/3.5.0/lib/python3.5/site-packages/bitly_api/__init__.py", line 1, in <module>
    from bitly_api import Connection, BitlyError, Error
ImportError: cannot import name 'Connection'

django_ses try ... ʻexcept` statement I tried to import It falls in an instant. However, it seems that it has been corrected in master.

>>> import django_ses
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/csakatoku/.pyenv/versions/3.5.0/lib/python3.5/site-packages/django_ses/__init__.py", line 173
    except SESConnection.ResponseError, err:
                                      ^
SyntaxError: invalid syntax

pynliner SyntaxError by the print statement. Pull Request for Python 3 has been issued.

Collecting pynliner
  Using cached pynliner-0.5.2.tar.gz
Collecting BeautifulSoup<4.0,>=3.2.1 (from pynliner)
  Using cached BeautifulSoup-3.2.1.tar.gz
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 20, in <module>
      File "/tmp/pip-build-7je9i10s/BeautifulSoup/setup.py", line 22
        print "Unit tests have failed!"
                                      ^
    SyntaxError: Missing parentheses in call to 'print'

Code that needs correction

You have to pass binary as an argument of hashlib.sha1

Bad

>>> import hashlib
>>> hashlib.sha1("SPAM").hexdigest()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Unicode-objects must be encoded before hashing
>>> hashlib.sha1("SPAM").hexdigest()

Good

>>> import hashlib
>>> hashlib.sha1("spam".encode("utf-8")).hexdigest()
'ded982e702e07bb7b6effafdc353db3fe172c83f'

Good

>>> import hashlib
>>> hashlib.sha1(b"spam").hexdigest()
'ded982e702e07bb7b6effafdc353db3fe172c83f'

urllib.basejoin is gone

Where did you go

The argument of sort has changed

• https://docs.python.org/3.5/howto/sorting.html?highlight=sort#the-old-way-using-the-cmp-parameter

Bad

>>> data = [{"value": 1}, {"value": 3}, {"value": 2}]
>>> data.sort(lambda a, b: cmp(a["value"], b["value"]))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: must use keyword argument for key function

Good

>>> data = [{"value": 1}, {"value": 3}, {"value": 2}]
>>> data.sort(key=lambda x: x["value"])
>>> print(data)
[{'value': 1}, {'value': 2}, {'value': 3}]

This change is the tightest.