- C++14 supported compiler
- gcc 6.1+ (5+ may work)
- clang 6 (3.4+ may work)
- Visual Studio 2017+
- cmake (needed for bundled capnproto)
- ninja (macOS + Linux)
- Visual Studio 2017+
- capnproto-0.8.0 (0.7.0 will also work if linking to system libraries)
- Not necessary if using bundled capnproto
- Python development headers (i.e. Python.h)
- Distributables from python.org include these, however they are usually in a separate package on Linux distributions
32-bit Linux requires that capnproto be compiled with
-fPIC. This is usually set correctly unless you are compiling canproto yourself. This is also called
-DCMAKE_POSITION_INDEPENDENT_CODE=1 for cmake.
pycapnp has additional development dependencies, including cython and pytest. 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-8.2 pip install pycapnp.
Or you can clone the repo like so:
git clone https://github.com/capnproto/pycapnp.git cd pycapnp pip install .
If you wish to install using the latest upstream C++ Cap'n Proto:
pip install \ --install-option "--libcapnp-url" \ --install-option "https://github.com/capnproto/capnproto/archive/master.tar.gz" \ --install-option "--force-bundled-libcapnp" .
To force bundled python:
pip install --install-option "--force-bundled-libcapnp" .
Slightly more prompt error messages using distutils rather than pip.
python setup.py install --force-bundled-libcapnp
The bundling system isn't that smart so it might be necessary to clean up the bundled build when changing versions:
python setup.py clean
Python 3.7+ is supported. Earlier versions of Python have asyncio bugs that might be possible to work around, but may require significant work (3.5 and 3.6).
Git flow has been abandoned, use master.
To test, use a pipenv (or install requirements.txt and run pytest manually).
pip install pipenv pipenv install pipenv run pytest
Building a dumb binary distribution:
python setup.py bdist_dumb
Building a Python wheel distributiion:
python setup.py bdist_wheel
There is some basic documentation here.
Make sure to look at the examples. The examples are generally kept up to date with the recommended usage of the library.
The examples directory has one example that shows off pycapnp quite nicely. Here it is, reproduced:
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)