Python 3 migration

python-2-3.md

Notes on migrating packages from Python 2.7 to Python 2/3 cross-compatibility

General resources

• https://docs.python.org/3/howto/pyporting.html (more conceptual)
• http://sebastianraschka.com/Articles/2014_python_2_3_key_diff.html (more practical)
• six is a very helpful library for cross-version imports of things like urllib
• there are some automatic conversion utilities like futurize, but i'm skeptical

Dependencies

• check whether dependencies are already cross-compatible
• if newer dependency versions support only Python 3, you may need to do extra testing and/or adjust how the dependencies are specified
• e.g., Matplotlib 3.x supports only Python 3, and pip at one point was having trouble figuring out what to install for Python 2.7

Updating syntax

• print statements: print → print() (latter is cross-version)
• integer division: can be implicit in Python 2.7, but must be explicit in Python 3
• unicode handled natively by the str type in python 3 (check places where you read or write data)
• exceptions: raise Error, "error" → raise Error("error") (latter is cross-version)
• urllib: info 1, info 2