Py2Jl

Python-to-Julia transpiler. Python 3 semantics are used (see below).

Usage

For now, because of a bug in Julia itself, long-term-support (LTS) versions of Julia, e.g. Julia 1.0.4 and 1.0.0 do not work. The package intends to support LTS Julia too, and will as soon as Julia is fixed.

Th package now works on 1.1.x, and before on Julia 1.1.0-rc2, but earlier versions, at least those named LTS ones, do segfault.

pkg> add Py2Jl

To demonstrate, open a file (check out demo.jl) and write

using Py2Jl

py2jl"""
def sum_by(f, seq):
    s = 0
    for e in seq:
        s = s + f(e)
    return s
"""
@info sum_by(x -> 2x, [1, 2, 3]) # 12

@info py2jl("mymod", """
def sum_by(f, seq):
    s = 0
    for e in seq:
        s = s + e
    return s
""")

Then type julia demo.jl in your shell to see the results.

Motivation

Since packages written in Julia are quite few, and Python is exactly a subset of Julia despite some implementation details, it's natural to think about taking advantage of existing Python codebase in Julia ecosystem so that we can have a great number of powerful and battle-tested packages.

Status

Currently, we can transpile a single Python module with limited constructs into Julia ones.

Supported Features

All the basic constructs like if-else, for, while, etc
while-else, for-else constructs
Function invocation with keyword args and variadic args
Arbitrary try-excepts
Annotation (but not equivalent to Julia's)

Not Implemented (yet) Features

Function definitions with keyword args (both kwargs and so-called keyword arg), default args and variadic args
Classes
Imports (dynamically importing might not be supported forever)
Attributes (obj.attr)
Python-compatible built-in functions like map, print and many standard libs

Python 3 vs. older Python

Most of the differences between Python 2 and Python 3 do not matter, as not yet implemented. E.g. this valid Python 2 code translates, but with Python 3 semantics:

julia> py2jl"""
       def divide_by_two(x):
         return x/2
       """

julia> divide_by_two(9)  # Python 2, unlike Python 3 and Julia would return 4.
4.5

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