Form class definition in Django - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Django form validation?

Given the following Django form class and data, what will be the value of form.is_valid() and form.errors after validation?

Django

from django import forms

class ContactForm(forms.Form):
    name = forms.CharField(max_length=50)
    email = forms.EmailField()

form = ContactForm(data={'name': 'Alice', 'email': '[e-mail]'})
valid = form.is_valid()
errors = form.errors

A valid is True, errors is an empty dictionary

B valid is True, errors contains 'email' key

C valid is False, errors contains 'name' key

D valid is False, errors contains 'email' key

💡 Hint

Check if the provided email matches the EmailField format and if all required fields are present.

The form has both required fields filled correctly. The email is valid, so form.is_valid() returns True and form.errors is empty.

📝 Syntax

intermediate

Which option correctly defines a Django form with a required integer field?

Select the code snippet that correctly defines a Django form class with a required integer field named age.

A

class AgeForm(forms.Form):
    age = forms.IntegerField(required=False)

B

class AgeForm(forms.Form):
    age = forms.IntegerField(required=True)

C

class AgeForm(forms.Form):
    age = forms.CharField(required=True)

D

class AgeForm(forms.Form):
    age = forms.FloatField(required=True)

💡 Hint

Look for the field type that accepts only integers and is required.

Option B uses IntegerField with required=True, which matches the requirement exactly. Option B makes it optional. Option B uses CharField, which accepts strings. Option B uses FloatField, which accepts floats.

❓ state_output

advanced

What is the cleaned_data content after form validation?

Given this Django form and input data, what will form.cleaned_data contain after calling form.is_valid()?

Django

from django import forms

class SignupForm(forms.Form):
    username = forms.CharField(max_length=30)
    age = forms.IntegerField()

form = SignupForm(data={'username': 'bob', 'age': '25'})
form.is_valid()
cleaned = form.cleaned_data

A {'username': 'bob', 'age': 25}

B {'username': 'bob', 'age': '25'}

C {'username': 'bob'}

D Raises ValidationError

💡 Hint

Remember that IntegerField converts input strings to integers in cleaned_data.

The form converts the 'age' string '25' to integer 25 in cleaned_data after validation.

🔧 Debug

advanced

Why does this Django form raise a TypeError?

Examine the following form class. Why does instantiating it with data cause a TypeError?

Django

from django import forms

class ProfileForm(forms.Form):
    bio = forms.CharField(max_length=100)

form = ProfileForm(data='not a dict')

A Because forms.Form cannot be instantiated with data argument

B Because CharField requires an integer max_length

C Because data must be a dictionary or QueryDict, not a string

D Because bio field is missing a required argument

💡 Hint

Check the type expected for the data parameter when creating a form instance.

The data argument must be a dictionary-like object. Passing a string causes a TypeError.

🧠 Conceptual

expert

Which statement about Django form class definition is true?

Select the correct statement about defining and using Django form classes.

A Form classes cannot have custom validation methods

B Form fields can only be defined inside the __init__ method of the form class

C Django forms automatically save data to the database when is_valid() is called

D A form class must inherit from forms.Form and define fields as class attributes

💡 Hint

Think about how Django expects form fields to be declared.

Django form classes inherit from forms.Form and define fields as class attributes. Custom validation methods are allowed. Forms do not save data automatically.