Server IP : 103.119.228.120 / Your IP : 3.15.186.56 Web Server : Apache System : Linux v8.techscape8.com 3.10.0-1160.119.1.el7.tuxcare.els2.x86_64 #1 SMP Mon Jul 15 12:09:18 UTC 2024 x86_64 User : nobody ( 99) PHP Version : 5.6.40 Disable Function : shell_exec,symlink,system,exec,proc_get_status,proc_nice,proc_terminate,define_syslog_variables,syslog,openlog,closelog,escapeshellcmd,passthru,ocinum cols,ini_alter,leak,listen,chgrp,apache_note,apache_setenv,debugger_on,debugger_off,ftp_exec,dl,dll,myshellexec,proc_open,socket_bind,proc_close,escapeshellarg,parse_ini_filepopen,fpassthru,exec,passthru,escapeshellarg,escapeshellcmd,proc_close,proc_open,ini_alter,popen,show_source,proc_nice,proc_terminate,proc_get_status,proc_close,pfsockopen,leak,apache_child_terminate,posix_kill,posix_mkfifo,posix_setpgid,posix_setsid,posix_setuid,dl,symlink,shell_exec,system,dl,passthru,escapeshellarg,escapeshellcmd,myshellexec,c99_buff_prepare,c99_sess_put,fpassthru,getdisfunc,fx29exec,fx29exec2,is_windows,disp_freespace,fx29sh_getupdate,fx29_buff_prepare,fx29_sess_put,fx29shexit,fx29fsearch,fx29ftpbrutecheck,fx29sh_tools,fx29sh_about,milw0rm,imagez,sh_name,myshellexec,checkproxyhost,dosyayicek,c99_buff_prepare,c99_sess_put,c99getsource,c99sh_getupdate,c99fsearch,c99shexit,view_perms,posix_getpwuid,posix_getgrgid,posix_kill,parse_perms,parsesort,view_perms_color,set_encoder_input,ls_setcheckboxall,ls_reverse_all,rsg_read,rsg_glob,selfURL,dispsecinfo,unix2DosTime,addFile,system,get_users,view_size,DirFiles,DirFilesWide,DirPrintHTMLHeaders,GetFilesTotal,GetTitles,GetTimeTotal,GetMatchesCount,GetFileMatchesCount,GetResultFiles,fs_copy_dir,fs_copy_obj,fs_move_dir,fs_move_obj,fs_rmdir,SearchText,getmicrotime MySQL : ON | cURL : ON | WGET : ON | Perl : ON | Python : ON | Sudo : ON | Pkexec : ON Directory : /usr/local/ssl/local/ssl/local/ssl/local/ssl/lib64/python2.7/Demo/metaclasses/ |
Upload File : |
"""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. """ from Meta import MetaClass, MetaHelper, MetaMethodWrapper class EiffelMethodWrapper(MetaMethodWrapper): def __init__(self, func, inst): MetaMethodWrapper.__init__(self, func, inst) # Note that the following causes recursive wrappers around # the pre-/post-condition testing methods. These are harmless # but inefficient; to avoid them, the lookup must be done # using the class. try: self.pre = getattr(inst, self.__name__ + "_pre") except AttributeError: self.pre = None try: self.post = getattr(inst, self.__name__ + "_post") except AttributeError: self.post = None def __call__(self, *args, **kw): if self.pre: apply(self.pre, args, kw) Result = apply(self.func, (self.inst,) + args, kw) if self.post: apply(self.post, (Result,) + args, kw) return Result class EiffelHelper(MetaHelper): __methodwrapper__ = EiffelMethodWrapper class EiffelMetaClass(MetaClass): __helper__ = EiffelHelper Eiffel = EiffelMetaClass('Eiffel', (), {}) def _test(): class C(Eiffel): def m1(self, arg): return arg+1 def m1_pre(self, arg): assert arg > 0, "precondition for m1 failed" def m1_post(self, Result, arg): assert Result > arg x = C() x.m1(12) ## x.m1(-1) if __name__ == '__main__': _test()