More thorough docs are available at http://jparyani.github.io/pycapnp/.
pycapnp's distribution has no requirements beyond a C++11 compatible compiler. GCC 4.8+ or Clang 3.3+ should work fine.
pycapnp has additional development dependencies, including cython and py.test. See requirements.txt for them all.
Building and installation
pip install pycapnp. You can set the CC environment variable to control which compiler is used, ie
CC=gcc-4.8 pip install pycapnp.
Or you can clone the repo like so:
git clone https://github.com/jparyani/pycapnp.git pip install --install-option '--force-cython' ./pycapnp
Note: for OSX, if using clang from Xcode 5, you may need to set
CFLAGS like so:
CFLAGS='-stdlib=libc++' pip install pycapnp
Python 2.6/2.7 are supported as well as Python 3.2+. PyPy 2.1+ is also supported.
One oddity to note is that
Text type fields will be treated as byte strings under Python 2, and unicode strings under Python 3.
Data fields will always be treated as byte strings.
This project uses git-flow. Essentially, just make sure you do your changes in the
develop branch. You can run the tests by installing pytest with
pip install pytest, and then run
py.test from the
In order to build binary packages from this source code, you must specify the
Building a dumb binary distribution:
python setup.py bdist_dumb --disable-cython
Building a Python wheel distributiion:
python setup.py bdist_wheel --disable-cython
If it fails with an error like
clang: error: no such file or directory: 'capnp/lib/capnp.cpp', then you need to cythonize fist. This can be done with:
python setup.py build --force-cython
There is some basic documentation here.
The examples directory has one example that shows off pycapnp quite nicely. Here it is, reproduced:
from __future__ import print_function import os import capnp import addressbook_capnp def writeAddressBook(file): addresses = addressbook_capnp.AddressBook.new_message() people = addresses.init('people', 2) alice = people alice.id = 123 alice.name = 'Alice' alice.email = 'email@example.com' alicePhones = alice.init('phones', 1) alicePhones.number = "555-1212" alicePhones.type = 'mobile' alice.employment.school = "MIT" bob = people bob.id = 456 bob.name = 'Bob' bob.email = 'firstname.lastname@example.org' bobPhones = bob.init('phones', 2) bobPhones.number = "555-4567" bobPhones.type = 'home' bobPhones.number = "555-7654" bobPhones.type = 'work' bob.employment.unemployed = None addresses.write(file) def printAddressBook(file): addresses = addressbook_capnp.AddressBook.read(file) for person in addresses.people: print(person.name, ':', person.email) for phone in person.phones: print(phone.type, ':', phone.number) which = person.employment.which() print(which) if which == 'unemployed': print('unemployed') elif which == 'employer': print('employer:', person.employment.employer) elif which == 'school': print('student at:', person.employment.school) elif which == 'selfEmployed': print('self employed') print() if __name__ == '__main__': f = open('example', 'w') writeAddressBook(f) f = open('example', 'r') printAddressBook(f)
Also, pycapnp has gained RPC features that include pipelining and a promise style API. Refer to the calculator example in the examples directory for a much better demonstration:
import capnp import socket import test_capability_capnp class Server(test_capability_capnp.TestInterface.Server): def __init__(self, val=1): self.val = val def foo(self, i, j, **kwargs): return str(i * 5 + self.val) def server(write_end): server = capnp.TwoPartyServer(write_end, bootstrap=Server(100)) def client(read_end): client = capnp.TwoPartyClient(read_end) cap = client.bootstrap() cap = cap.cast_as(test_capability_capnp.TestInterface) remote = cap.foo(i=5) response = remote.wait() assert response.x == '125' if __name__ == '__main__': read_end, write_end = socket.socketpair(socket.AF_UNIX) # This is a toy example using socketpair. # In real situations, you can use any socket. server(write_end) client(read_end)
If you get an error on installation like:
... gcc-4.8: error: capnp/capnp.c: No such file or directory gcc-4.8: fatal error: no input files
Then you have too old a version of setuptools. Run
pip install -U setuptools then try again.