int3 / js2py

A Javascript-to-Python translation assistant.

js2py

A Javascript-to-Python translation assistant. It does a simple translation from Javascript to Python (as detailed below). You'll most likely need to make further changes by hand, but this automates part of the work.

I thought it would be nice to be able to import some libraries directly into Python, rather than shelling out to NodeJS. This script is the result of trying to make that a reality.

I've successfully used it to port Esprima to Python -- the result is PyEsprima.

Setup & Usage

npm install
./js2py.coffee file.js > out.py

Transformations and Shims

• Create global declarations where necessary
• Transform simple prototype-based classes into corresponding Python classes (but no inheritance)
• Remove assignment statements from conditional tests
• Convert switch statements into if-else chains
• Convert pre-/post-increments into assignment statements
• Array.prototype.slice and String.prototype.substr are converted to Python's slice notation
• Function expressions are hoisted out as fully declared functions since Python's lambdas are limited
• Shims for RegExp and JS-style dictionaries
• Some support for typeof

Limitations

• No support for modifying non-global nonlocals (but easy enough to add with the nonlocal keyword in Python 3)
• a[i] in JS will return undefined if i >= a.length, but in Python it raises an IndexError.
• No support for call / apply.
• There many more; pull requests are welcome!