Different types of validators in web2py

Multiple validators

The multiple validators are used when we want to validate and do multiple validations on a single value. The output of a validator is passed on to the next validator as input. If any of the validators fail, all the other validators will also fail, displaying an error message.

Custom validators

We can create custom validators and make them act similarly to pre-defined ones. We can call the validators and return the value we want when the validation is successful. If not, we can display the error message.

def valid(str):
	if (type)str == string:
		return 1
	return 0
	
str = “coding ninjas - validators”
if valid(s):
	print(“valid”)
else:
	error_message = “invalid”
	print(error_message)

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The above code validates when the given input is a string and prints ”valid” or displays an error message “invalid”.

Validators with dependencies

There are few cases when the result of the validator may depend on another validator. If we consider a registration form an example, we retype our password to confirm it. But if we leave the password field empty in the first field, we cannot validate if the password re-entered by the user is equal to the first one.  

def index():
    form = SQLFORM.factory(
        Field('username', requires=IS_NOT_EMPTY()),
        Field('password', requires=IS_NOT_EMPTY()),
        Field('password_again',
              requires=IS_EQUAL_TO(request.vars.password, error_message=”passwords are not matched”)))

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In the above code, we take the username and password values from the user and store them in the database. When we enter a password, the validator checks if the password is empty and validates if the password re-entered by the user is the same as the one entered before. If both the passwords are not matched, an error message is displayed, as shown below.

Other validators

We also have other validators that do not come under the categories mentioned above. Let’s discuss a validator CLEANUP in this section.

CLEANUP

This validator is more like a filter, so this never fails. We don’t use the error_message argument in this validator, as we don’t have a case of validation failure. This validator can be used by passing a regular expression to it. If not by default, it will remove all the characters from the expression whose ASCII values are not in the list [10, 13, 32-127]. 

CLEANUP('[^\d]')('Hello 123 world 456')

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The d in the above code represents digits, and all the characters that are not digits are removed from the above regular expression, and the output will be “123456”.

Frequently Asked Questions

What are the different types of validators?

There are different types of validators provided by web2py. They are; security, complexity, special type, text, date and time, range, set and equity, database, custom, multiple, and dependency validators. 

Does the CLEANUP validator remove whitespaces and unnecessary characters too?

The CLEANUP validator performs the initial strip and removes the leading(beginning of the line) and trailing(end of the line) whitespaces in a regular expression.

Why do we use arguments in validators?

We use arguments in validators to provide extra information and conditions to perform the validation. For example, we check if a name is alphanumeric using the IS_ALPHANUMERIC validator, to which we can add an error_message argument to display an error in case of validation failure.

Conclusion

We have discussed the concept of different types of validators in web2py in this article. You can now start coding in your preferred language.

Check out this problem - Duplicate Subtree In Binary Tree

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