Validation

Field

from django import forms

class ContactForm(forms.Form):
    message = forms.CharField(
            widget = forms.Textarea(),
            initial = "Replace with your feedback.")

    def clean_message(self):
        message = self.cleaned_data.get('message', '')
        num_words = len(message.split())
        if num_words < 4:
            raise forms.ValidationError("Not enough words!")
        return message

Note:

• Also see Validation

• The clean_message method will be called after the default field validator.

• Because the field data has already been partially processed, we need to pull it out of the form’s clean_data dictionary.

• If the user has entered too few words, we raise a ValidationError. The string attached to this exception will be displayed to the user as an item in the error list.

• It is important that we explicitly return the value for the field at the end of the method. This allows us to modify the value (or convert it to a different Python type) within our custom validation method.

  If we forget the return statement, then None will be returned, and the original value will be lost.

Form

def clean(self):
    data = self.cleaned_data
    if there_is_a_non_field_specific_error:
        raise forms.ValidationError("I am not happy with this form.")
    return data

class ContactForm(forms.Form):
    ...

    def clean(self):
        cleaned_data = self.cleaned_data
        cc_myself = cleaned_data.get("cc_myself")
        subject = cleaned_data.get("subject")

        if cc_myself and subject and "help" not in subject:
            # (see link below for discussion)
            msg = u"Must put 'help' in subject when cc'ing yourself."
            self._errors["cc_myself"] = self.error_class([msg])
            self._errors["subject"] = self.error_class([msg])

            # These fields are no longer valid. Remove them from the
            # cleaned data.
            del cleaned_data["cc_myself"]
            del cleaned_data["subject"]

        # Always return the full collection of cleaned data.
        return cleaned_data

For details, see Cleaning and validating fields that depend on each other.

CSS

The <ul> has a class attribute of errorlist. The following CSS makes our errors stand out:

<style type="text/css">
    ul.errorlist {
        margin: 0;
        padding: 0;
    }
    .errorlist li {
        background-color: red;
        color: white;
        display: block;
        font-size: 10px;
        margin: 0 0 3px;
        padding: 4px 5px;
    }
</style>