Form Validation
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Checking Validity
is_valid() runs all field validators and returns True only if every field passes.
Example: Checking Validity
is_valid() runs all field validators and returns True only if every field passes.
form = ContactForm(request.POST)
if form.is_valid():
print(form.cleaned_data['email'])Reading Cleaned Data
cleaned_data is a dictionary of validated, type-converted values, only available after is_valid() succeeds.
Example: Reading Cleaned Data
cleaned_data is a dictionary of validated, type-converted values, only available after is_valid() succeeds.
form = ContactForm(request.POST)
if form.is_valid():
name = form.cleaned_data['name']
email = form.cleaned_data['email']Displaying Errors
When validation fails, form.errors holds a dictionary of field names to error messages, shown automatically by {{ form.as_p }}.
Example: Displaying Errors
When validation fails, form.errors holds a dictionary of field names to error messages, shown automatically by {{ form.as_p }}.
<form method="post">
{% csrf_token %}
{{ form.as_p }}
<button type="submit">Send</button>
</form>- Reading request.POST values directly instead of calling form.is_valid() first, skipping validation entirely.
- Accessing form.cleaned_data before calling is_valid(), which raises an error because cleaning hasn't run yet.
- Assuming client-side HTML5 validation (like required) is enough, ignoring that the server must always re-validate.
- Calling form.is_valid() runs every field's validation and populates form.cleaned_data on success.
- Invalid submissions automatically attach error messages to form.errors for each bad field.
- Never trust data straight from request.POST — always validate through the form first.
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