Alterando atributos do widget no Form

forms.py

from django import forms

class MeuForm(forms.Form):
    
    campo1 = forms.CharField(label="Campo 1")
    
    def __init__(self, *args, **kwargs):
        super(MeuForm, self).__init__(*args, **kwargs)
        self.fields["campo1"].widget.attrs["class"] = "classe_css1"