ASN.1 String Types

ASN.1 defines a variety of string types used to represent textual data. All generated Python classes for these string types will wrap the native Python str type. This applies to the following ASN.1 string types:

  • IA5String

  • PrintableString

  • VisibleString

  • ISO646String

  • NumericString

  • UniversalString

  • BMPString

  • UTF8String

  • GeneralString

  • GraphicString

  • TeletexString (T61String)

  • VideotexString

  • ObjectDescriptor

  • UTCTime

  • GeneralizedTime

Example ASN.1 definition:

MyUTF8String ::= UTF8String
MyPrintable ::= PrintableString

which generate Python classes roughly equivalent to:

class MyUTF8String(_Asn1BasicType[str]):
    pass

class MyPrintable(_Asn1BasicType[str]):
    pass

Conceptual Representation

class _Asn1BasicType[str]

Represents an ASN.1 string type.

__init__(self, value: str | None = None) → None

Initializes the string type instance with an optional initial value.

The value must be a Python str or None.

property value: str

Gets or sets the string value.

Setting the value accepts any Python object coercible to str, such as string literals or other string-like objects.

Important

The string is expected to conform to the ASN.1 string type’s character repertoire and constraints; however, validation is performed by the constraint checking methods.

Character Sets and Constraints

Each ASN.1 string type restricts the allowed characters differently. For example:

  • PrintableString allows a limited set of printable characters.

  • IA5String corresponds roughly to ASCII.

  • UTF8String supports the full Unicode set.

The generated classes enforce these constraints via validation and raise exceptions if invalid data is assigned and packed.

Note

Mutating the returned string is not possible since Python strings are immutable. To change the value, assign a new string explicitly.