def filter_field(key, fields, func=None):
"""
Run a field through the given filter, or default if none is provided. If
field doesn't exist, it will attempt to return the default value for that
field.
:param key: the field name to use
:param fields: a dictionary of available fields in the form ``name: value``
:returns: Filtered value
:raises: KeyError in the event the field can't be found among the provided
ones or the defaults
"""
try:
val = fields[key]
except KeyError:
default_fields = getattr(settings, 'PUBLISH_FIELD_DEFAULTS', {})
FIELD_DEFAULTS.update(default_fields)
try:
val = FIELD_DEFAULTS[key]
except KeyError:
raise ConfigurationError('You must supply the `%s` field in the'
' article, via settings.PUBLISH_FIELD_DEFAULTS, or'
' via command line (where applicable)' % key)
default_filters = getattr(settings, 'PUBLISH_FILTER_DEFAULTS', {})
FILTER_DEFAULTS.update(default_filters)
f = func or FILTER_DEFAULTS[key]
return f(val)
