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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _construct_qs_filter(self, field_name):
 """ Using a field name optionnaly prefixed by `^`, `=`, `@`, return a case-insensitive filter condition name usable as a queryset `filter()` keyword argument. """

        if field_name.startswith('^'):
            return "%s__istartswith" % field_name[1:]
        elif field_name.startswith('='):
            return "%s__iexact" % field_name[1:]
        elif field_name.startswith('@'):
            return "%s__search" % field_name[1:]
        else:
            return "%s__icontains" % field_name