A Python to optimized JavaScript translator inspired by PythonJS and Rusthon. It parses Python with the standard ast module and emits clean, fast JavaScript.

• Prototype-based classes — Python class and def __init__ become JS constructor + ClassName.prototype.method
• Minimal runtime — Only a small __range() helper for range(); no heavy runtime
• Built-in mappings — print → console.log, len(x) → x.length, int/float/str → Number/String, etc.
• List/dict literals — Native [] and {}
• List/dict comprehensions — Transpiled to for...of loops with array/object accumulation
• Control flow — if/for/while/try/except with correct semantics (including for/while-else)

From the project root:

pip install -e .

Or run without installing:

python -m py2js Examples/hello.py -o out.js

CLI

# stdin → stdout
python -m py2js < script.py

# file → file
python -m py2js script.py -o script.js

# Options
python -m py2js script.py -o script.js --no-runtime --indent "  "

API

from py2js import transpile

js = transpile("""
class Greeter:
    def __init__(self, name):
        self.name = name
    def greet(self):
        return "Hello, " + self.name + "!"

g = Greeter("World")
print(g.greet())
""")
print(js)

• Classes: var ClassName = function(...) { this.__init__.apply(this, arguments); }; and ClassName.prototype.__init__ = function(...) { ... };
• Methods: ClassName.prototype.methodName = function(...) { ... };
• self: Omitted in JS; this is used as the instance

• Functions, async functions
• Classes with __init__ and methods
• Assignments (including tuple unpacking)
• if / elif / else, for / while (with else and break/continue)
• try / except / finally, raise, assert
• Expressions: literals, names, comparisons, and/or/not, arithmetic, subscript, attribute, call
• List/dict/tuple literals, list/dict comprehensions, lambda
• print, range, len, int, float, str, list, dict, min, max, sum, abs
• Imports are commented out (no runtime resolution)

• PythonJS blog — Original Python→JS ideas and WebWorkers/Go backends
• Rusthon blog — Fork with faster JS and benchmarks

MIT