Date: 2009-09-14

Tags: zope, python

Railsのbefore_filterっぽい仕組みをPythonのデコレータで実装

以前Railsで作った某アプリをPythonに移植中です。出来るだけPythonの流儀に組み直してるんですが、Railsのbefore_filterを分かりやすく組み替えるのが思いつかなかったので、Pythonで同じようなことをする仕組みを作ってみました。と言ってもzope.formlibのActionsから8割くらいコードをパクってきてます。

目的は以下のようなにコードを用意すれば、indexアクションやcreateアクションが呼ばれる前に２つの事前処理関数が実行されるようにすること。

Rubyだとこう。

class FooController < ApplicatoinController
  before_filter :setup1, :setup2

  def index
    render ...
  end

  def create
    user = User.new(params[:user])
    user.save()
    render ...
  end

  def setup1
    ...
  end

  def setup2
    ...
  end
end

Pythonでこうしたい。

class FooController(ApplicationController):
    def index(self):
        self.render(...)

    def create(self)
        user = User(self.request.get(user))
        user.put()
        render ...
    end

    @hook('before')
    def setup1(self):
        ...

    @hook('before')
    def setup2(self):
        ...

これで、呼び出したい関数にhookデコレータでマーキング出来たので、親クラスApplicationControllerに、@hook('before')で登録した関数を呼び出すための仕組みを仕込めば完成！

ってことで、hookデコレータを実装している hooks.py のソースコード。

import sys

__all__ = ['hook', 'Hooks']

class Hook(object):
    def __init__(self, timing, func):
        self.timing = timing
        self.func = func

    def __call__(self, *args, **kw):
        return self.func(self.inst, *args, **kw)

    def __get__(self, inst, class_=None):
        if inst is None:
            return self
        result = self.__class__.__new__(self.__class__)
        result.__dict__.update(self.__dict__)
        result.inst = inst
        return result


class hook:
    def __init__(self, timing=None, hooks=None):
        caller_locals = sys._getframe(1).f_locals
        if hooks is None:
            hooks = caller_locals.get('hooks')
        if hooks is None:
            hooks = caller_locals['hooks'] = Hooks()
        self.hooks = hooks
        self.timing = timing

    def __call__(self, func):
        hook = Hook(self.timing, func)
        self.hooks.append(hook)
        return hook


class Hooks(object):
    def __init__(self, *hooks):
        self._hooks = hooks

    def __iter__(self):
        return iter(self._hooks)

    def __len__(self):
        return len(self._hooks)

    def append(self, hook):
        self._hooks += (hook,)

    @classmethod
    def exec_hooks(klass, obj, timing=None):
        [x() for x in obj.hooks if timing in [None, x.timing]]

    # TODO need test
    def __add__(self, other):
        return self.__class__(*(self._hooks + other._hooks))

    def copy(self):
        return self.__class__(*self._hooks)

    def __get__(self, inst, class_):
        if inst is None:
            return self
        return self.__class__(*[a.__get__(inst) for a in self._hooks])

使い方、兼、テストコード。

import unittest
from hooks import hook, Hooks

class HooksTest(unittest.TestCase):
    def test_register_hook(self):
        class Base(object):
            @hook()
            def func1(self):
                pass
        obj = Base()
        self.assertEqual(1, len(obj.hooks))

    def test_call_func(self):
        class Base(object):
            value = 0
            @hook()
            def func1(self):
                self.value = 1
        obj = Base()
        Hooks.exec_hooks(obj)
        self.assertEqual(1, obj.value)

    def test_hooks_does_not_inherit(self):
        class Base(object):
            value1 = 0
            @hook()
            def func1(self):
                self.value1 = 1
        class Derive(Base):
            value2 = 0
            @hook()
            def func2(self):
                self.value2 = 2
        obj = Derive()
        Hooks.exec_hooks(obj)
        self.assertEqual(0, obj.value1) # value1 was inherited, but not hooked
        self.assertEqual(2, obj.value2)

    def test_hooks_can_inherit(self):
        class Base(object):
            value1 = 0
            @hook()
            def func1(self):
                self.value1 = 1
        class Derive(Base):
            hooks = Base.hooks.copy()
            value2 = 0
            @hook()
            def func2(self):
                self.value2 = 2
        obj = Derive()
        Hooks.exec_hooks(obj)
        self.assertEqual(1, obj.value1)
        self.assertEqual(2, obj.value2)

        obj = Base()
        Hooks.exec_hooks(obj)
        self.assertEqual(1, obj.value1)
        self.assert_(not hasattr(obj, 'value2'))


    def test_inherited_brother_hooks_must_not_pollution(self):
        class Base(object):
            value1 = 0
            @hook()
            def func1(self):
                self.value1 = 1
        class DeriveA(Base):
            value2 = 0
            @hook()
            def func2(self):
                self.value2 = 2
        class DeriveB(Base):
            value3 = 0
            @hook()
            def func3(self):
                self.value3 = 3

        obj = Base()
        Hooks.exec_hooks(obj)
        self.assertEqual(1, obj.value1)
        self.assert_(not hasattr(obj, 'value2'))
        self.assert_(not hasattr(obj, 'value3'))

        obj = DeriveA()
        Hooks.exec_hooks(obj)
        self.assertEqual(0, obj.value1) # value1 was inherited, but not hooked
        self.assertEqual(2, obj.value2)
        self.assert_(not hasattr(obj, 'value3'))

        obj = DeriveB()
        Hooks.exec_hooks(obj)
        self.assertEqual(0, obj.value1) # value1 was inherited, but not hooked
        self.assert_(not hasattr(obj, 'value2'))
        self.assertEqual(3, obj.value3)

    def test_inherit_hooks_must_not_pollution(self):
        class Base(object):
            value1 = 0
            @hook()
            def func1(self):
                self.value1 = 1
        class DeriveA(Base):
            hooks = Base.hooks.copy()
            value2 = 0
            @hook()
            def func2(self):
                self.value2 = 2
        class DeriveB(Base):
            value3 = 0
            @hook()
            def func3(self):
                self.value3 = 3

        obj = DeriveB()
        Hooks.exec_hooks(obj)
        self.assertEqual(0, obj.value1) # value1 was inherited, but not hooked
        self.assertEqual(3, obj.value3)
        self.assert_(not hasattr(obj, 'value2'))

    def test_register_named_hooks(self):
        class Base(object):
            value1 = 0
            value2 = 0
            value3 = 0
            @hook()
            def func1(self):
                self.value1 = 1
            @hook('foo')
            def func2(self):
                self.value2 = 2
            @hook('bar')
            def func3(self):
                self.value3 = 3

        obj = Base()
        Hooks.exec_hooks(obj)
        self.assertEqual(1, obj.value1)
        self.assertEqual(2, obj.value2)
        self.assertEqual(3, obj.value3)

        obj = Base()
        Hooks.exec_hooks(obj, 'foo')
        self.assertEqual(0, obj.value1)
        self.assertEqual(2, obj.value2)
        self.assertEqual(0, obj.value3)

        obj = Base()
        Hooks.exec_hooks(obj, 'bar')
        self.assertEqual(0, obj.value1)
        self.assertEqual(0, obj.value2)
        self.assertEqual(3, obj.value3)

        obj = Base()
        Hooks.exec_hooks(obj, 'baz')
        self.assertEqual(0, obj.value1)
        self.assertEqual(0, obj.value2)
        self.assertEqual(0, obj.value3)


def test_suite():
    return unittest.TestSuite((
        TestSuite(HooksTest),
    ))

if __name__ == '__main__':
    unittest.main()

@hook デコレータを使うと、使ったクラスのクラス変数に勝手にhooksを追加します。あしからず。

今回、このコードを理解するために、frameと__get__の仕組みを勉強しました。先人のコード(今回はzope.formlib)は勉強になるね。