future-fstrings

future-fstrings

A backport of fstrings to python<3.6.

Installation

pip install future-fstrings

Usage

Include the following encoding cookie at the top of your file (this replaces the utf-8 cookie if you already have it):

# -*- coding: future_fstrings -*-

And then write python3.6 fstring code as usual!

# -*- coding: future_fstrings -*-
thing = 'world'
print(f'hello {thing}')

$ python2.7 main.py
hello world

Showing transformed source

future-fstrings also includes a cli to show transformed source.

$ future-fstrings-show main.py
# -*- coding: future_fstrings -*-
thing = 'world'
print('hello {}'.format((thing)))

Transform source for micropython

The future-fstrings-show command can be used to transform source before distributing. This can allow you to write f-string code but target platforms which do not support f-strings, such as micropython.

To use this on modern versions of python, install using:

pip install future-fstrings[rewrite]

and then use future-fstrings-show as above.

For instance:

future-fstrings-show code.py > code_rewritten.py

How does this work?

future-fstrings has two parts:

1. A utf-8 compatible codec which performs source manipulation
   • The codec first decodes the source bytes using the UTF-8 codec
   • The codec then leverages tokenize-rt to rewrite f-strings.
2. A .pth file which registers a codec on interpreter startup.

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