Python extension and './configure'

Recently I have been working on python-rrdtool Python binding to rrdtool utility.

On PyPI there has already existed py-rrdtool package, but it did not work at all.

It turned out, that rrdtool sources had a nice looking rrdtoolmodule.c, all I needed was to compile it.

Long story short: rrdtoolmodule.c includes a non-existent header, which is created during ./configure run. So I had to figure out how to call ./configure from inside setup.py script.

(You may take a look at actual setup.py instead of reading this blog post.)

from distutils.core import setup, Command
from distutils.command.build_ext import build_ext
...
setup(
    ...
    cmdclass={"build_configure": BuildConfigure, "build_ext": BuildExtension},
    ...
)

In order to run ./configure at specific moment before your module is being built, you have to use distutils command extensions: build_configure and build_ext.

class BuildConfigure(Command):
    def run(self):
        # run `./configure` here, I did it using subprocess module
        ...

BuildConfigure class has to call the configure executable. But this class is not enough, distutils requires special building extension.

class BuildExtension(build_ext):
    def run(self):
        for cmd_name in self.get_sub_commands():
            self.run_command(cmd_name)

        build_ext.run(self)

    sub_commands = [("build_configure", None)] + build_ext.sub_commands

I override run method to explicitly run our commands. In sub_commands list of 2-element tuples, first element stays for command extension, and second for usage circumstances (None == always, function == depending on it’s boolean output).

Note: if you happen to see “permission error” somewhere, make sure that you set chmods for configure executable:

os.chmod(executable, 0777)