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-   -   Re: avoid the redefinition of a function (http://www.velocityreviews.com/forums/t952117-re-avoid-the-redefinition-of-a-function.html)

Jabba Laci 09-12-2012 04:56 PM

Re: avoid the redefinition of a function
 
> 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

MRAB 09-12-2012 06:33 PM

Re: avoid the redefinition of a function
 
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"


D'Arcy Cain 09-12-2012 09:49 PM

Re: avoid the redefinition of a function
 
On Wed, 12 Sep 2012 18:04:51 GMT
Alister <alister.ware@ntlworld.com> wrote:
> 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)


http://xkcd.com/327/

--
D'Arcy J.M. Cain <darcy@druid.net> | Democracy is three wolves
http://www.druid.net/darcy/ | and a sheep voting on
+1 416 425 1212 (DoD#0082) (eNTP) | what's for dinner.
IM: darcy@Vex.Net

Peter Otten 09-13-2012 08:23 AM

Re: avoid the redefinition of a function
 
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()




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