Because From is in FROZEN, it'll be signed twice (related to: https://bugs.launchpad.net/dkimpy/+bug/799175). If implementations don't want to sign From twice, they have to remove it from frozen_sign and add it to should_sign which seems like an oversight in the API.
For example dkim_obj.frozen_sign = set([]) dkim_obj.should_sign.add('from')
Otherwise signing will fail, because From is not included.
Because From is in FROZEN, it'll be signed twice (related to: https:/ /bugs.launchpad .net/dkimpy/ +bug/799175). If implementations don't want to sign From twice, they have to remove it from frozen_sign and add it to should_sign which seems like an oversight in the API.
For example
dkim_obj. frozen_ sign = set([])
dkim_obj. should_ sign.add( 'from')
Otherwise signing will fail, because From is not included.