SET

The ASN.1 SET type represents an unordered collection of fields, similar to SEQUENCE, but without guaranteed ordering.

Like SEQUENCE, each field can be mandatory or optional, and may have default values. However, encoding rules for SET allow fields to appear in any order.

Attention

Default values are still in development!

Example ASN.1 definition:

Preferences ::= SET {
    color           UTF8String OPTIONAL,
    notifications   BOOLEAN DEFAULT TRUE,
    timezone        INTEGER
}

generates the following Python class:

class Preferences(_Asn1Type):
    color: str | None
    notifications: bool
    timezone: int

    def __init__(
        self,
        color: str | None = ...,
        notifications: bool = ...,
        timezone: int = ...
    ) -> None: ...

In Python, each ASN.1 SET generates a class similar to a SEQUENCE class, but with the following key differences:

  • Explicit Assignment Required: All fields must be explicitly assigned valid values before encoding; internally, the class tracks which fields have been set.

  • Default Return of None: Accessing any unset field returns None by default, regardless of whether it is optional or has a default value.

  • The order of fields does not affect the encoding.

Conceptual Representation

class _Asn1SetType

Represents an ASN.1 SET.

__init__(self, *, field1: Any = ..., field2: Any = ..., ...) → None

Initializes a new SET instance.

  • All fields are initialized as unset (None).

  • Fields must be explicitly assigned before encoding.

  • Fields are passed as keyword arguments only.

field_name

Access or set the value of the field named field_name.

  • Getting a field returns None if it has not been explicitly assigned.

  • Setting a field marks it as assigned and stores the given value.

Example Usage in Python:

prefs = Preferences()
prefs.color = "blue"
prefs.timezone = 5
print(prefs.notifications)  # None, since not assigned explicitly
encoded = prefs.ber_encode()