Choice type

class pyasn1.type.univ.Choice(componentType=None, tagSet=tagSet(), subtypeSpec=ConstraintsIntersection())

Create Choice schema or value object.

Choice class is based on ConstructedAsn1Type, its objects are mutable and duck-type Python list objects.

Keyword Arguments

  • componentType (NamedType) – Object holding named ASN.1 types allowed within this collection

  • tagSet (TagSet) – Object representing non-default ASN.1 tag(s)

  • subtypeSpec (ConstraintsIntersection) – Object representing non-default ASN.1 subtype constraint(s). Constraints verification for Choice type can only occur on explicit .isInconsistent call.

Examples

class Afters(Choice):
    '''
    ASN.1 specification:

    Afters ::= CHOICE {
        cheese  [0] IA5String,
        dessert [1] IA5String
    }
    '''
    componentType = NamedTypes(
        NamedType('cheese', IA5String().subtype(
            implicitTag=Tag(tagClassContext, tagFormatSimple, 0)
        ),
        NamedType('dessert', IA5String().subtype(
            implicitTag=Tag(tagClassContext, tagFormatSimple, 1)
        )
    )

afters = Afters()
afters['cheese'] = 'Mascarpone'

Note

The Choice type can only hold a single component at a time belonging to the list of allowed types.

clone(componentType=None, tagSet=tagSet(), subtypeSpec=ConstraintsIntersection())

Create a modified version of Choice schema object.

The clone() method accepts the same set arguments as Choice class takes on instantiation except that all arguments of the clone() method are optional.

Whatever arguments are supplied, they are used to create a copy of self taking precedence over the ones used to instantiate self.

Possible values of self are never copied over thus clone() can only create a new schema object.

Returns

new instance of Choice type/value

Note

Due to the mutable nature of the Choice object, even if no arguments are supplied, a new Choice object will be created and returned.

subtype(componentType=None, implicitTag=Tag(), explicitTag=Tag(), subtypeSpec=ConstraintsIntersection())

Create a specialization of Choice schema object.

The subtype() method accepts the same set arguments as Choice class takes on instantiation except that all parameters of the subtype() method are optional.

With the exception of the arguments described below, the rest of supplied arguments they are used to create a copy of self taking precedence over the ones used to instantiate self.

The following arguments to subtype() create a ASN.1 subtype out of Choice type.

Other Parameters

  • implicitTag (Tag) – Implicitly apply given ASN.1 tag object to self’s TagSet, then use the result as new object’s ASN.1 tag(s).

  • explicitTag (Tag) – Explicitly apply given ASN.1 tag object to self’s TagSet, then use the result as new object’s ASN.1 tag(s).

  • subtypeSpec (ConstraintsIntersection) – Add ASN.1 constraints object to one of the self’s, then use the result as new object’s ASN.1 constraints.

Returns

new instance of Choice type/value

Note

Due to the mutable nature of the Choice object, even if no arguments are supplied, a new Choice object will be created and returned.

tagSet = <TagSet object, untagged>

Set (on class, not on instance) or return a TagSet object representing ASN.1 tag(s) associated with Choice type.

componentType = <NamedTypes object, types >

Default collection of ASN.1 types of component (e.g. NamedType) object representing ASN.1 type allowed within Choice type

subtypeSpec = <ConstraintsIntersection object, consts <ValueSizeConstraint object, consts 1, 1>>

Set (on class, not on instance) or return a ConstraintsIntersection object imposing constraints on Choice type initialization values.

getComponentByPosition(idx, default=<NoValue object>, instantiate=True)

Returns Choice type component by index.

Equivalent to Python sequence subscription operation (e.g. []).

Parameters

idx (int) – Component index (zero-based). Must either refer to an existing component or (if componentType is set) new ASN.1 schema object gets instantiated.

Keyword Arguments

  • default (object) – If set and requested component is a schema object, return the default object instead of the requested component.

  • instantiate (bool) – If True (default), inner component will be automatically instantiated. If False either existing component or the NoValue object will be returned.

Returns

PyAsn1Item – a PyASN1 object

Examples

# can also be Set
class MySequence(Sequence):
    componentType = NamedTypes(
        NamedType('id', OctetString())
    )

s = MySequence()

# returns component #0 with `.isValue` property False
s.getComponentByPosition(0)

# returns None
s.getComponentByPosition(0, default=None)

s.clear()

# returns noValue
s.getComponentByPosition(0, instantiate=False)

# sets component #0 to OctetString() ASN.1 schema
# object and returns it
s.getComponentByPosition(0, instantiate=True)

# sets component #0 to ASN.1 value object
s.setComponentByPosition(0, 'ABCD')

# returns OctetString('ABCD') value object
s.getComponentByPosition(0, instantiate=False)

s.clear()

# returns noValue
s.getComponentByPosition(0, instantiate=False)
setComponentByPosition(idx, value=<NoValue object>, verifyConstraints=True, matchTags=True, matchConstraints=True)

Assign Choice type component by position.

Equivalent to Python sequence item assignment operation (e.g. []).

Parameters

idx (int) – Component index (zero-based). Must either refer to existing component or to N+1 component. In the latter case a new component type gets instantiated (if componentType is set, or given ASN.1 object is taken otherwise) and appended to the Choice sequence.

Keyword Arguments

  • value (object or PyAsn1Item derivative) – A Python value to initialize Choice component with (if componentType is set) or ASN.1 value object to assign to Choice component. Once a new value is set to idx component, previous value is dropped. If value is not given, schema object will be set as a component.

  • verifyConstraints (bool) – If False, skip constraints validation

  • matchTags (bool) – If False, skip component tags matching

  • matchConstraints (bool) – If False, skip component constraints matching

Returns

self

property effectiveTagSet

Return a TagSet object of the currently initialized component or self (if Choice is tagged).

property tagMap

“Return a TagMap object mapping ASN.1 tags to ASN.1 objects contained within callee.

getComponent(innerFlag=False)

Return currently assigned component of the Choice object.

Returns

PyAsn1Item – a PyASN1 object

getName(innerFlag=False)

Return the name of currently assigned component of the Choice object.

Returns

str – Choice component name

property isValue

Indicate that Choice object represents ASN.1 value.

If isValue is False then this object represents just ASN.1 schema.

If isValue is True then, in addition to its ASN.1 schema features, this object can also be used like a Python built-in object (e.g. int, str, dict etc.).

Returns

bool – False if object represents just ASN.1 schema. True if object represents ASN.1 schema and can be used as a normal value.

Note

There is an important distinction between PyASN1 schema and value objects. The PyASN1 schema objects can only participate in ASN.1 schema-related operations (e.g. defining or testing the structure of the data). Most obvious uses of ASN.1 schema is to guide serialisation codecs whilst encoding/decoding serialised ASN.1 contents.

The PyASN1 value objects can additionally participate in many operations involving regular Python objects (e.g. arithmetic, comprehension etc).

isSameTypeWith(other, matchTags=True, matchConstraints=True)

Examine Choice type for equality with other ASN.1 type.

ASN.1 tags (tag) and constraints (constraint) are examined when carrying out ASN.1 types comparison.

Python class inheritance relationship is NOT considered.

Parameters

other (a pyasn1 type object) – Class instance representing ASN.1 type.

Returns

bool – True if other is Choice type, False otherwise.

isSuperTypeOf(other, matchTags=True, matchConstraints=True)

Examine Choice type for subtype relationship with other ASN.1 type.

ASN.1 tags (tag) and constraints (constraint) are examined when carrying out ASN.1 types comparison.

Python class inheritance relationship is NOT considered.

Parameters

other (a pyasn1 type object) – Class instance representing ASN.1 type.

Returns

bool – True if other is a subtype of Choice type, False otherwise.

getComponentByName(name, default=<NoValue object>, instantiate=True)

Returns Choice type component by name.

Equivalent to Python dict subscription operation (e.g. []).

Parameters

name (str) – Choice type component name

Keyword Arguments

  • default (object) – If set and requested component is a schema object, return the default object instead of the requested component.

  • instantiate (bool) – If True (default), inner component will be automatically instantiated. If False either existing component or the NoValue object will be returned.

Returns

PyAsn1Item – Instantiate Choice component type or return existing component value

setComponentByName(name, value=<NoValue object>, verifyConstraints=True, matchTags=True, matchConstraints=True)

Assign Choice type component by name.

Equivalent to Python dict item assignment operation (e.g. []).

Parameters

name (str) – Choice type component name

Keyword Arguments

  • value (object or PyAsn1Item derivative) – A Python value to initialize Choice component with (if componentType is set) or ASN.1 value object to assign to Choice component. If value is not given, schema object will be set as a component.

  • verifyConstraints (bool) – If False, skip constraints validation

  • matchTags (bool) – If False, skip component tags matching

  • matchConstraints (bool) – If False, skip component constraints matching

Returns

self

getComponentByType(tagSet, default=<NoValue object>, instantiate=True, innerFlag=False)

Returns Choice type component by ASN.1 tag.

Parameters

tagSet (TagSet) – Object representing ASN.1 tags to identify one of Choice object component

Keyword Arguments

  • default (object) – If set and requested component is a schema object, return the default object instead of the requested component.

  • instantiate (bool) – If True (default), inner component will be automatically instantiated. If False either existing component or the noValue object will be returned.

Returns

PyAsn1Item – a pyasn1 object

setComponentByType(tagSet, value=<NoValue object>, verifyConstraints=True, matchTags=True, matchConstraints=True, innerFlag=False)

Assign Choice type component by ASN.1 tag.

Parameters

tagSet (TagSet) – Object representing ASN.1 tags to identify one of Choice object component

Keyword Arguments

  • value (object or PyAsn1Item derivative) – A Python value to initialize Choice component with (if componentType is set) or ASN.1 value object to assign to Choice component. If value is not given, schema object will be set as a component.

  • verifyConstraints (bool) – If False, skip constraints validation

  • matchTags (bool) – If False, skip component tags matching

  • matchConstraints (bool) – If False, skip component constraints matching

  • innerFlag (bool) – If True, search for matching tagSet recursively.

Returns

self

property isInconsistent

Run necessary checks to ensure Choice object consistency.

Default action is to verify Choice object against constraints imposed by subtypeSpec.

Raises

PyAsn1tError –