I have been attempting to create a vacation filter using the add_to_filterset function, as per the following example. I have reduced the actual parameters for the purpose of this issue, but the error is still replicated:

    from sievelib import factory
    
    filter_set = factory.FiltersSet
    
    filter_set.addfilter(
        "test_autoresponder", [(
            "Subject", ":matches", "*"
        )], [(
            "vacation",
            ":subject", "Example Autoresponder Subject",
            ":days", 7,
            ":mime",
            "Example Autoresponder Body"
        )]
    )

This gives an AttributeError: AttributeError: 'int' object has no attribute 'startswith'

The offending code appears to be this line (https://github.com/tonioo/sievelib/blob/1.2.1/sievelib/factory.py#L260):

if arg.startswith(":"):

Obviously the startswith method is not present on Python integers. In addition, attempting to cast the int to a string results in a commands.BadValue Exception being raised.

Delving into the commands.py module, it is clear the VacationCommand definition is accepting a argument of type "number" (https://github.com/tonioo/sievelib/blob/1.2.1/sievelib/commands.py#L1026), which according to the above code reference, seems as if it can never be passed in via the factory.

I believe the factory.py method should be updated to check for numeric arguments, and pass in the appropriate "number" type via atype = "number".

I have only just started to use sievelib so please forgive any ignorance in this issue, but I would be happy to submit a pull request if required.