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https://github.com/google/grumpy

Grumpy is a Python to Go source code transcompiler and runtime.
https://github.com/google/grumpy

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Grumpy is a Python to Go source code transcompiler and runtime.

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README 

        
# Grumpy: Go running Python



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## Overview



Grumpy is a Python to Go source code transcompiler and runtime that is intended

to be a near drop-in replacement for CPython 2.7. The key difference is that it

compiles Python source code to Go source code which is then compiled to native

code, rather than to bytecode. This means that Grumpy has no VM. The compiled Go

source code is a series of calls to the Grumpy runtime, a Go library serving a

similar purpose to the Python C API (although the API is incompatible with

CPython's).



## Limitations



### Things that will probably never be supported by Grumpy



1. `exec`, `eval` and `compile`: These dynamic features of CPython are not

   supported by Grumpy because Grumpy modules consist of statically-compiled Go

   code. Supporting dynamic execution would require bundling Grumpy programs

   with the compilation toolchain, which would be unwieldy and impractically

   slow.



2. C extension modules: Grumpy has a different API and object layout than

   CPython and so supporting C extensions would be difficult. In principle it's

   possible to support them via an API bridge layer like the one that

   [JyNI](http://jyni.org) provides for Jython, but it would be hard to maintain and

   would add significant overhead when calling into and out of extension

   modules.



### Things that Grumpy will support but doesn't yet



There are three basic categories of incomplete functionality:



1. [Language features](https://github.com/google/grumpy/wiki/Missing-features#language-features):

   Most language features are implemented with the notable exception of

   [old-style classes](http://stackoverflow.com/questions/54867/what-is-the-difference-between-old-style-and-new-style-classes-in-python).

   There are also a handful of operators that aren't yet supported.



2. [Builtin functions and types](https://github.com/google/grumpy/wiki/Missing-features#builtins):

   There are a number of missing functions and types in `__builtins__` that have

   not yet been implemented. There are also a lot of methods on builtin types

   that are missing.



3. [Standard library](https://github.com/google/grumpy/wiki/Missing-features#standard-libraries):

   The Python standard library is very large and much of it is pure Python, so

   as the language features and builtins get filled out, many modules will

   just work. But there are also a number of libraries in CPython that are C

   extension modules which will need to be rewritten.



4. C locale support: Go doesn't support locales in the same way that C does. As such,

   some functionality that is locale-dependent may not currently work the same as in

   CPython.



## Running Grumpy Programs



### Method 1: make run:



The simplest way to execute a Grumpy program is to use `make run`, which wraps a

shell script called grumprun that takes Python code on stdin and builds and runs

the code under Grumpy. All of the commands below are assumed to be run from the

root directory of the Grumpy source code distribution:



```

echo "print 'hello, world'" | make run

```



### Method 2: grumpc and grumprun:



For more complicated programs, you'll want to compile your Python source code to

Go using grumpc (the Grumpy compiler) and then build the Go code using `go

build`. Since Grumpy programs are statically linked, all the modules in a

program must be findable by the Grumpy toolchain on the GOPATH. Grumpy looks for

Go packages corresponding to Python modules in the \_\_python\_\_ subdirectory

of the GOPATH. By convention, this subdirectory is also used for staging Python

source code, making it similar to the PYTHONPATH.



The first step is to set up the shell so that the Grumpy toolchain and libraries

can be found. From the root directory of the Grumpy source distribution run:



```

make

export PATH=$PWD/build/bin:$PATH

export GOPATH=$PWD/build

export PYTHONPATH=$PWD/build/lib/python2.7/site-packages

```



You will know things are working if you see the expected output from this

command:



```

echo 'import sys; print sys.version' | grumprun

```



Next, we will write our simple Python module into the \_\_python\_\_ directory:



```

echo 'def hello(): print "hello, world"' > $GOPATH/src/__python__/hello.py

```



To build a Go package from our Python script, run the following:



```

mkdir -p $GOPATH/src/__python__/hello

grumpc -modname=hello $GOPATH/src/__python__/hello.py > \

    $GOPATH/src/__python__/hello/module.go

```



You should now be able to build a Go program that imports the package

"\_\_python\_\_/hello". We can also import this module into Python programs

that are built using grumprun:



```

echo 'from hello import hello; hello()' | grumprun

```



grumprun is doing a few things under the hood here:



1. Compiles the given Python code to a dummy Go package, the same way we

   produced \_\_python\_\_/hello/module.go above

2. Produces a main Go package that imports the Go package from step 1. and

   executes it as our \_\_main\_\_ Python package

3. Executes `go run` on the main package generated in step 2.



## Developing Grumpy



There are three main components and depending on what kind of feature you're

writing, you may need to change one or more of these.



### grumpc



Grumpy converts Python programs into Go programs and `grumpc` is the tool

responsible for parsing Python code and generating Go code from it. `grumpc` is

written in Python and uses the [`pythonparser`](https://github.com/m-labs/pythonparser)

module to accomplish parsing.



The grumpc script itself lives at `tools/grumpc`. It is supported by a number of

Python modules in the `compiler` subdir.



### Grumpy Runtime



The Go code generated by `grumpc` performs operations on data structures that

represent Python objects in running Grumpy programs. These data structures and

operations are defined in the `grumpy` Go library (source is in the runtime

subdir of the source distribution).  This runtime is analogous to the Python C

API and many of the structures and operations defined by `grumpy` have

counterparts in CPython.



### Grumpy Standard Library



Much of the Python standard library is written in Python and thus "just works"

in Grumpy. These parts of the standard library are copied from CPython 2.7

(possibly with light modifications). For licensing reasons, these files are kept

in the `third_party` subdir.



The parts of the standard library that cannot be written in pure Python, e.g.

file and directory operations, are kept in the `lib` subdir. In CPython these

kinds of modules are written as C extensions. In Grumpy they are written in

Python but they use native Go extensions to access facilities not otherwise

available in Python.



### Source Code Overview



- `compiler`: Python package implementating Python -> Go transcompilation logic.

- `lib`: Grumpy-specific Python standard library implementation.

- `runtime`: Go source code for the Grumpy runtime library.

- `third_party/ouroboros`: Pure Python standard libraries copied from the

   [Ouroboros project](https://github.com/pybee/ouroboros).

- `third_party/pypy`: Pure Python standard libraries copied from PyPy.

- `third_party/stdlib`: Pure Python standard libraries copied from CPython.

- `tools`: Transcompilation and utility binaries.



## Contact



Questions? Comments? Drop us a line at [[email protected]](https://groups.google.com/forum/#!forum/grumpy-users)

or join our [Gitter channel](https://gitter.im/grumpy-devel/Lobby)