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
>
> 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 ...
That's a typical case for using an OO approach; just make a class for
each validator and have a single polymorphic validate method (I would
make validators __call__able instead of naming the method 'validate'):
# Abstract Validator class; not strictly necessary but good for
documentation
class Validator(object):
def __call__(self,field,value):
'''Validate a value for this field.
Return a string representation of value on success, or None on
failure.
'''
raise NotImplementedError("Abstract method")
class DecimalValidator(Validator):
def __call__(self,name,value):
'''Test whether numeric value is a decimal.'''
class ZipCodeValidator(Validator):
def __call__(self,name,value):
'''Test if value is a US Zip Code.'''
def validateField(name, value, validators):
""" Validates field input """
results = {}
for validate in validators:
result = validate(name,value)
if result is not None:
results[name] = result
# XXX: if more than one validators succeed,
# all but the last result will be overwritten
return results
# test
validators = [DecimalValidator(), ZipCodeValidator()]
print validateField("home ZIP", "94303", validators)
Regards,
George
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