BitString type

class pyasn1.type.univ.BitString(value=NoValue(), tagSet=TagSet(), subtypeSpec=ConstraintsIntersection(), namedValues=NamedValues(), binValue=NoValue(), hexValue=NoValue())

Create BitString schema or value object.

BitString class is based on SimpleAsn1Type, its objects are immutable and duck-type both Python tuple (as a tuple of bits) and int objects.

Keyword Arguments

  • value (int, str or BitString object) – Python int or str literal representing binary or hexadecimal number or sequence of integer bits or BitString object. If value is not given, schema object will be created.

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

  • subtypeSpec (ConstraintsIntersection) – Object representing non-default ASN.1 subtype constraint(s). Constraints verification for BitString type occurs automatically on object instantiation.

  • namedValues (NamedValues) – Object representing non-default symbolic aliases for numbers

  • binValue (str) – Binary string initializer to use instead of the value. Example: ‘10110011’.

  • hexValue (str) – Hexadecimal string initializer to use instead of the value. Example: ‘DEADBEEF’.

Raises

ValueConstraintError, PyAsn1Error – On constraint violation or bad initializer.

Examples

class Rights(BitString):
    '''
    ASN.1 specification:

    Rights ::= BIT STRING { user-read(0), user-write(1),
                            group-read(2), group-write(3),
                            other-read(4), other-write(5) }

    group1 Rights ::= { group-read, group-write }
    group2 Rights ::= '0011'B
    group3 Rights ::= '3'H
    '''
    namedValues = NamedValues(
        ('user-read', 0), ('user-write', 1),
        ('group-read', 2), ('group-write', 3),
        ('other-read', 4), ('other-write', 5)
    )

group1 = Rights(('group-read', 'group-write'))
group2 = Rights('0011')
group3 = Rights(0x3)

Note

The BitString type models an arbitrary sequence of bits.

clone(value=NoValue(), tagSet=TagSet(), subtypeSpec=ConstraintsIntersection(), namedValues=NamedValues(), binValue=NoValue(), hexValue=NoValue())

Create a modified version of BitString schema or value object.

The clone() method accepts the same set arguments as BitString 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.

Note

Due to the immutable nature of the BitString object, if no arguments are supplied, no new BitString object will be created and self will be returned instead.

subtype(value=NoValue(), implicitTag=Tag(), explicitTag=Tag(), subtypeSpec=ConstraintsIntersection(), namedValues=NamedValues(), binValue=NoValue(), hexValue=NoValue())

Create a specialization of BitString schema or value object.

The subtype relationship between ASN.1 types has no correlation with subtype relationship between Python types. ASN.1 type is mainly identified by its tag(s) (TagSet) and value range constraints (ConstraintsIntersection). These ASN.1 type properties are implemented as BitString attributes.

The subtype() method accepts the same set arguments as BitString 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 BitString 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 BitString schema or value object

Note

Due to the immutable nature of the BitString object, if no arguments are supplied, no new BitString object will be created and self will be returned instead.

tagSet = <TagSet object, tags 0:0:3>

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

subtypeSpec = <ConstraintsIntersection object>

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

asNumbers()

Get BitString value as a sequence of 8-bit integers.

If BitString object length is not a multiple of 8, result will be left-padded with zeros.

asOctets()

Get BitString value as a sequence of octets.

If BitString object length is not a multiple of 8, result will be left-padded with zeros.

asInteger()

Get BitString value as a single integer value.

asBinary()

Get BitString value as a text string of bits.

classmethod fromHexString(value, internalFormat=False, prepend=None)

Create a BitString object initialized from the hex string.

Parameters

value (str) – Text string like ‘DEADBEEF’

classmethod fromBinaryString(value, internalFormat=False, prepend=None)

Create a BitString object initialized from a string of ‘0’ and ‘1’.

Parameters

value (str) – Text string like ‘1010111’

classmethod fromOctetString(value, internalFormat=False, prepend=None, padding=0)

Create a BitString object initialized from a string.

Parameters

value (str (Py2) or bytes (Py3)) – Text string like ‘\x01\xff’ (Py2) or b’\x01\xff’ (Py3)

property isValue

Indicate that BitString 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 BitString 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 BitString type, False otherwise.

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

Examine BitString 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 BitString type, False otherwise.

property effectiveTagSet

For BitString type is equivalent to tagSet

property tagMap

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