Iterate through a list calling functions

[Kent Johnson]

David Pratt wrote:
> Hi.  I am creating methods for form validation. Each validator has its 
> own method and there quite a number of these.  For each field, I want to 
> evaluate errors using one or more  validators so I want to execute the 
> appropriate validator methods from those available.  I am iterating over 
> each validator using validateField method to gather my results. It works 
> but it ugly and inefficient.  Can someone advise whether there is a 
> better way of doing this.  I realize that the validator variable in my 
> iteration is only a string so question is how can I make the validator 
> string reference a function so I may be able to shorten validateField to 
> something similar to this (instead of my long list of ifs which I am not 
> very happy with):
> 
>     for validator in validators_list:
>         result = validator(name, value)
>         if type (result) in StringTypes:
>         results[name] = result

Actually you can do exactly that by putting references to the validator functions in your list instead of (string) name. For example if you have
validators = [ 'isDecimal', 'isFoo', 'isBar' ]

just change it to
validators = [ isDecimal, isFoo, isBar ]

and your loop above will work.

Python makes data-driven programming easy :-)
Kent

> 
> Many thanks
> David
> 
> My current situation below:
> 
> # A large list of validators
> def isDecimal(name, value):
>     """ Test whether numeric value is a decimal """
>     result = validateRegex(name,
>         value,
>         r'^([+-]?)(?=\d|\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?$',
>         errmsg='is not a decimal number.',
>         ignore=None)
>     return result
> 
> def isZipCode(name, value):
>     """ Tests if field value is a US Zip Code """
>     result = validateRegex(name,
>         value,
>         r'^(\d{5}|\d{9})$',
>         errmsg='is not a valid zip code.',
>         ignore=None)
>     return result
> 
> ... more validators
> 
> # Iterating over validators to gather field errors
> def validateField(name, value, validators_list, range=None, 
> valid_values=None):
>     """ Validates field input """
>     results={}   
>     for validator in validators_list:
>         if validator == 'isContainedIn':
>             result = isContainedIn(name, value)
>             if type (result) in StringTypes:
>                 more...
>         if validator == 'isDate':
>             result = isDate(name, value)
>             if type (result) in StringTypes:
>                 more...
>         if validator == 'isDecimal':
>             result = isDecimal(name, value)
>             if type (result) in StringTypes:
>                 more...
> 
>                  more validators ...
>