avoid the redefinition of a function

[Peter Otten]

MRAB wrote:

> On 12/09/2012 19:04, Alister wrote:
>> On Wed, 12 Sep 2012 18:56:46 +0200, Jabba Laci wrote:
>>
>>>> For example:
>>>>
>>>> def install_java():
>>>>    pass
>>>>
>>>> def install_tomcat():
>>>>    pass
>>>
>>> Thanks for the answers. I decided to use numbers in the name of the
>>> functions to facilitate function calls. Now if you have this menu option
>>> for instance:
>>>
>>> (5) install mc
>>>
>>> You can type just "5" as user input and step_5() is called
>>> automatically. If I use descriptive names like install_java() then
>>> selecting a menu point would be more difficult. And I don't want users
>>> to type "java", I want to stick to simple numbers.
>>>
>>> Laszlo
>>
>> No No NO!
>> you cant just pass user input to system calls without validating it first
>> (google sql injection for examples of the damage unsanitised input can
>> cause, it is not just as SQL problem)
>>
>> it is just as easy so select a reasonably named function as a bad one
>>
>> option=raw_input('select your option :')
>>
>> if option =="1": install_java()
>> if option =="2": install_other()
>>
>> alternatively you cold add your functions into a dictionary an call them
>> from that
>>
>> opts={'1':install java,'2':install_other}
>>
>> option=raw_input('select your option :')
>> opts[option]
>>
>> Poorly named functions are a major example of poor programming style.
>>
>> one of the fundamental pillars for python is readability!
>>
> Or you could do this:
> 
> 
> def install_java():
>      "Install Java"
>      print "Installing Java"
> 
> def install_tomcat():
>      "Install Tomcat"
>      print "Installing Tomcat"
> 
> menu = [install_java, install_tomcat]
> 
> for index, func in enumerate(menu, start=1):
>      print "{0}) {1}".format(index, func.__doc__)
> 
> option = raw_input("Select your option : ")
> 
> try:
>      opt = int(option)
> except ValueError:
>      print "Not a valid option"
> else:
>      if 1 <= opt < len(menu):
>          menu[opt - 1]()
>      else:
>          print "Not a valid option"

I'd still argue that a function index is the wrong approach. You can use tab 
completion to make entering descriptive names more convenient:

import cmd

class Cmd(cmd.Cmd):
    prompt = "Enter a command (? for help): "

    def do_EOF(self, args):
        return True
    def do_quit(self, args):
        return True

    @classmethod
    def install_command(class_, f):
        def wrapped(self, arg):
            if arg:
                print "Discarding argument {!r}".format(arg)
            return f()

        wrapped.__doc__ = f.__doc__
        wrapped.__name__ = f.__name__
        class_._add_method("do_" + f.__name__, wrapped)
        return f

    @classmethod
    def _add_method(class_, methodname, method):
        if hasattr(class_, methodname):
            raise ValueError("Duplicate command {!r}".format(methodname))
        setattr(class_, methodname, method)

command = Cmd.install_command

@command
def install_java():
     "Install Java"
     print "Installing Java"

@command
def install_tomcat():
     "Install Tomcat"
     print "Installing Tomcat"

if __name__ == "__main__":
    Cmd().cmdloop()