django tempalte filter for french contraction for "à les", "à le", "à la"

french_grammar_tags.py

from django import template

register = template.Library()


@register.filter(is_safe=False)
def à(value, upper=False, capitalize=False):
    """
    French contraction for "à les", "à le", "à la"

    if string starts with le or Le, replace it with "au"
    if string starts with les or Les, replace it with "aux"
    if string starts with la, replace it with "à la"
    if strings starts with l', replace it with "à l'" and
        hopes for the best ( this is not sexist, this is
        statistically correct )
    if string starts with à, do nothing
    if string starts with au, do nothing
    if strings start with aux , do nothing

    upper = upper(value)
    capitalize = capitalize(value)
    """
    def capital(value):
        if upper:
            return value.upper()
        if capitalize:
            return value.capitalize()
        return value

    if value.startswith(('à ', 'au ', 'aux ')):
        return capital(value)

    if value.startswith(('le ', 'Le ', 'Au ')):
        return capital('au ' + value[3:])

    if value.startswith(('les ', 'Les ', 'Aux')):
        return capital('aux ' + value[4:])

    if value.startswith('À '):
        return capital('à ' + value[2:])

    return capital('au ' + value)