SET OF / SEQUENCE OF

The ASN.1 SET OF and SEQUENCE OF types represent an ordered or unordered collection of elements, respectively. Both contain zero or more elements of the same type.

  • SEQUENCE OF preserves the order of elements.

  • SET OF does not guarantee ordering in ASN.1 semantics, but in Python, both are represented in the same way using an ordered list interface for convenience.

Example ASN.1 definitions:

MySeqOfInts ::= SEQUENCE OF INTEGER
MySetOfStrings ::= SET OF UTF8String

generate the following Python classes:

class MySeqOfInts(_Asn1ListType[int]):
    pass

class MySetOfStrings(_Asn1ListType[str]):
    pass

Generated Python classes for SET OF and SEQUENCE OF behave like Python lists with type restrictions. All elements must be of the specified ASN.1 type (or compatible Python type).

The concept of the list type is described in _Asn1ListType.

Behavior

  • Both SET OF and SEQUENCE OF use the same list-like Python API.

  • Python’s ordering is preserved for both, even though ASN.1 SET OF does not define ordering.

  • Elements can be iterated over directly:

seq = MySeqOfInts([1, 2, 3])
for value in list(seq): # direct iterator not implemented
    print(value)

  • Elements can be added via add() or extend():

seq.add(4)
seq.extend([5, 6])

  • Conversion to a standard Python list is simple:

values = list(seq)

  • del can be used to remove items by index:

del seq[1]  # removes the second element