Go-like features for Python
Package golang provides Go-like features for Python:
- gpython is Python interpreter with support for lightweight threads.
- go spawns lightweight thread.
- chan and select provide channels with Go semantic.
- func allows to define methods separate from class.
- defer allows to schedule a cleanup from the main control flow.
- gimport allows to import python modules by full path in a Go workspace.
Command gpython provides Python interpreter that supports lightweight threads via tight integration with gevent. The standard library of GPython is API compatible with Python standard library, but inplace of OS threads lightweight coroutines are provided, and IO is internally organized via libuv/libev-based IO scheduler. Consequently programs can spawn lots of coroutines cheaply, and modules like time, socket, ssl, subprocess etc - all could be used from all coroutines simultaneously, and in the same blocking way as if every coroutine was a full OS thread. This gives ability to scale programs without changing concurrency model and existing code.
Additionally GPython sets UTF-8 to be default encoding always, and puts go, chan, select etc into builtin namespace.
GPython is optional and the rest of Pygolang can be used from under standard Python too. However without gevent integration go spawns full - not lightweight - OS thread.
Goroutines and channels
go spawns a coroutine, or thread if gevent was not activated. It is possible to exchange data in between either threads or coroutines via channels. chan creates a new channel with Go semantic - either synchronous or buffered. Use chan.recv, chan.send and chan.close for communication. select can be used to multiplex on several channels. For example:
ch1 = chan() # synchronous channel ch2 = chan(3) # channel with buffer of size 3 def _(): ch1.send('a') ch2.send('b') go(_) ch1.recv() # will give 'a' ch2.recv_() # will give ('b', True) _, _rx = select( ch1.recv, # 0 ch2.recv_, # 1 (ch2.send, obj2), # 2 default, # 3 ) if _ == 0: # _rx is what was received from ch1 ... if _ == 1: # _rx is (rx, ok) of what was received from ch2 ... if _ == 2: # we know obj2 was sent to ch2 ... if _ == 3: # default case ...
func decorator allows to define methods separate from class.
@func(MyClass) def my_method(self, ...): ...
will define MyClass.my_method().
func can be also used on just functions, for example:
@func def my_function(...): ...
Defer / recover / panic
defer allows to schedule a cleanup to be executed when current function returns. It is similar to try/finally but does not force the cleanup part to be far away in the end. For example:
wc = wcfs.join(zurl) │ wc = wcfs.join(zurl) defer(wc.close) │ try: │ ... ... │ ... ... │ ... ... │ finally: │ wc.close()
For completeness there is recover and panic that allow to program with Go-style error handling, for example:
def _(): r = recover() if r is not None: print("recovered. error was: %s" % (r,)) defer(_) ... panic("aaa")
But recover and panic are probably of less utility since they can be practically natively modelled with try/except.
If defer is used, the function that uses it must be wrapped with @func decorator.
gimport provides way to import python modules by full path in a Go workspace.
lonet = gimport('lab.nexedi.com/kirr/go123/xnet/lonet')
will import either
- lab.nexedi.com/kirr/go123/xnet/lonet.py, or
located in src/ under $GOPATH.
qq (import from golang.gcompat) provides %q functionality that quotes as Go would do. For example the following code will print name quoted in “ without escaping printable UTF-8 characters:
print('hello %s' % qq(name))
qq accepts both str and bytes (unicode and str on Python2) and also any other type that can be converted to str.
Package golang.strconv provides direct access to conversion routines, for example strconv.quote and strconv.unquote.
Benchmarking and testing
py.bench allows to benchmark python code similarly to go test -bench and py.test. For example, running py.bench on the following code:
def bench_add(b): x, y = 1, 2 for i in xrange(b.N): x + y
gives something like:
$ py.bench --count=3 x.py ... pymod: bench_add.py Benchmarkadd 50000000 0.020 µs/op Benchmarkadd 50000000 0.020 µs/op Benchmarkadd 50000000 0.020 µs/op
Package golang.testing provides corresponding runtime bits, e.g. testing.B.
py.bench produces output in Go benchmark format, and so benchmark results can be analyzed and compared with standard Go tools, for example with benchstat. Additionally package golang.x.perf.benchlib can be used to load and process such benchmarking data in Python.
Pygolang change history
- Provide gpython interpreter, that sets UTF-8 as default encoding, integrates gevent and puts go, chan, select etc into builtin namespace (commit).
- Fix select bug that was causing several cases to be potentially executed at the same time (commit 1, 2, 3).
- Add defer and recover (commit). The implementation is partly inspired by work of Denis Kolodin (1, 2).
- Fix @method on Python3 (commit).
- A leaked goroutine no longer prevents whole program to exit (commit 1, 2).
- Add py.bench program and golang.testing package with corresponding bits (commit).
- Turn into full pygolang: go, chan, select, method and gcompat.qq are provided in addition to gimport (commit). The implementation is not very fast, but should be working correctly including select - select sends for synchronous channels.
- Initial release; gimport functionality only (commit).