Useful functions to handle the class attribute of DOMNode.

useful_functions_to_handle_class_attr_of_DOMNode.py

"""Useful functions to handle the class attribute of DOMNode.

Usage:
```
>>> el = document['someid']
>>> add_class(el, 'class-one')
>>> add_class(el, 'old-class')
>>> change_class(el, 'old-class', 'new-class')
>>> remove_class(el, 'class-one')
>>> print(el.class_name)
```
"""

def add_class(el, class_):
    """Add class_ to el."""

    s = el.getAttribute('class') or ''
    if class_ in s.split():
        # already exists.
        return el

    s = '{old} {new}'.format(
        old=s,
        new=class_
    )
    el.setAttribute('class', s.strip())
    return el

def remove_class(el, class_):
    """Remove class_ from el."""

    s = el.getAttribute('class') or ''
    s = s.replace(class_, '')
    el.setAttribute('class', s)
    return el

def change_class(el, old, new_):
    """Change el's class from `old` to `new_`."""

    el = remove_class(el, old)
    el = add_class(el, new_)
    return el

Awesome! 😺