AlkantarClanX12

Your IP : 18.118.227.199

Current Path : /lib64/python2.7/Demo/metaclasses/
Upload File :
Current File : //lib64/python2.7/Demo/metaclasses/Eiffel.pyo

�
��^c@s�dZddlmZmZmZdefd��YZdefd��YZdefd��YZed	d
i�Zd
�Z	e
dkr�e	�ndS(s�Support Eiffel-style preconditions and postconditions.

For example,

class C:
    def m1(self, arg):
        require arg > 0
        return whatever
        ensure Result > arg

can be written (clumsily, I agree) as:

class C(Eiffel):
    def m1(self, arg):
        return whatever
    def m1_pre(self, arg):
        assert arg > 0
    def m1_post(self, Result, arg):
        assert Result > arg

Pre- and post-conditions for a method, being implemented as methods
themselves, are inherited independently from the method.  This gives
much of the same effect of Eiffel, where pre- and post-conditions are
inherited when a method is overridden by a derived class.  However,
when a derived class in Python needs to extend a pre- or
post-condition, it must manually merge the base class' pre- or
post-condition with that defined in the derived class', for example:

class D(C):
    def m1(self, arg):
        return arg**2
    def m1_post(self, Result, arg):
        C.m1_post(self, Result, arg)
        assert Result < 100

This gives derived classes more freedom but also more responsibility
than in Eiffel, where the compiler automatically takes care of this.

In Eiffel, pre-conditions combine using contravariance, meaning a
derived class can only make a pre-condition weaker; in Python, this is
up to the derived class.  For example, a derived class that takes away
the requirement that arg > 0 could write:

    def m1_pre(self, arg):
        pass

but one could equally write a derived class that makes a stronger
requirement:

    def m1_pre(self, arg):
        require arg > 50

It would be easy to modify the classes shown here so that pre- and
post-conditions can be disabled (separately, on a per-class basis).

A different design would have the pre- or post-condition testing
functions return true for success and false for failure.  This would
make it possible to implement automatic combination of inherited
and new pre-/post-conditions.  All this is left as an exercise to the
reader.

i����(t	MetaClasst
MetaHelpertMetaMethodWrappertEiffelMethodWrappercBseZd�Zd�ZRS(cCs�tj|||�yt||jd�|_Wntk
rLd|_nXyt||jd�|_Wntk
r�d|_nXdS(Nt_pret_post(Rt__init__tgetattrt__name__tpretAttributeErrortNonetpost(tselftfunctinst((s//usr/lib64/python2.7/Demo/metaclasses/Eiffel.pyRDs


cOsh|jrt|j||�nt|j|jf||�}|jrdt|j|f||�n|S(N(R	tapplyRRR(R
targstkwtResult((s//usr/lib64/python2.7/Demo/metaclasses/Eiffel.pyt__call__Ss		(Rt
__module__RR(((s//usr/lib64/python2.7/Demo/metaclasses/Eiffel.pyRBs	tEiffelHelpercBseZeZRS((RRRt__methodwrapper__(((s//usr/lib64/python2.7/Demo/metaclasses/Eiffel.pyR[stEiffelMetaClasscBseZeZRS((RRRt
__helper__(((s//usr/lib64/python2.7/Demo/metaclasses/Eiffel.pyR^stEiffelcCs0dtfd��Y}|�}|jd�dS(NtCcBs#eZd�Zd�Zd�ZRS(cSs|dS(Ni((R
targ((s//usr/lib64/python2.7/Demo/metaclasses/Eiffel.pytm1fscSsdS(N((R
R((s//usr/lib64/python2.7/Demo/metaclasses/Eiffel.pytm1_prehscSsdS(N((R
RR((s//usr/lib64/python2.7/Demo/metaclasses/Eiffel.pytm1_postjs(RRRRR(((s//usr/lib64/python2.7/Demo/metaclasses/Eiffel.pyRes		i(RR(Rtx((s//usr/lib64/python2.7/Demo/metaclasses/Eiffel.pyt_testds	t__main__N((t__doc__tMetaRRRRRRRR!R(((s//usr/lib64/python2.7/Demo/metaclasses/Eiffel.pyt<module>>s