How to migrate your code from python2 to python3?

Hey there and welcome back to the blog! Today we're going to look at how we can use an interesting tool called futurize in order to make those old python2 projects upto speed and compatible with python3!

Very recently, I had the opportunity to mentor an intern to develop a flask based microservice - development had started using python 2.7. Very quicky we realized that we needed to migrate this to run on a python 3.x release. Refactoring for these kind of changes is not a fun thing to do, and at the time, we had no option but to go about this manually.

Fast forward to today, I was talking to a colleague of mine about an interesting tool called Python-future. On looking into this more, it became apparent that I could have saved a lot of time for my intern had I known about this tool and how I can use it to update the code in a matter of seconds!

Installing Python-future

Installation of this is fairly straightforward. You can use your standanrd package managers in order to install python-future. Here's the command I used:

sudo apt-get install python-future

Now, for the sake of an example, lets take a very simple python2.7 based print statement and see how we can use python-future to update it to be python3.x compatible!

Here is my sample python2.x file called old_python.py:

print 'Hey, im written for python2.7'

Use the following command after installing python-future in order to preview the update old_python.py.

futurize old_python.py

A sample output of this:

root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
RefactoringTool: Skipping optional fixer: idioms
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
RefactoringTool: Skipping optional fixer: ws_comma
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
root: Generating grammar tables from /usr/lib/python2.7/lib2to3/PatternGrammar.txt
RefactoringTool: Refactored old_python.py
--- old_python.py    (original)
+++ old_python.py    (refactored)
@@ -1 +1,2 @@
-print 'Hey, im written for python2.7'
+from __future__ import print_function
+print('Hey, im written for python2.7')
RefactoringTool: Files that need to be modified:
RefactoringTool: old_python.py

And now, if you want to write these changes in place whilst creating a backup file so your old code is not lost, you can simply add the -w flag. See command below.

futurize -w old_python.py

And that's it! I'm glad I know about this tool now, and you do too! Hope you learned something new! :)

Some more reference information can be found here: https://www.activestate.com/blog/how-to-migrate-python-2-applications-to-python-3/

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