src/third_party/mozjs-45/python/pyasn1/doc/constraints.html - cobalt - Git at Google

 <html>
 <title>
 PyASN1 subtype constraints
 </title>
 <head>
 </head>
 <body>
 <center>
 <table width=60%>
 <tr>
 <td>

 <h4>
 1.4 PyASN1 subtype constraints
 </h4>

 <p>
 Most ASN.1 types can correspond to an infinite set of values. To adapt to
 particular application's data model and needs, ASN.1 provides a mechanism
 for limiting the infinite set to values, that make sense in particular case.
 </p>

 <p>
 Imposing value constraints on an ASN.1 type can also be seen as creating
 a subtype from its base type.
 </p>

 <p>
 In pyasn1, constraints take shape of immutable objects capable
 of evaluating given value against constraint-specific requirements.
 Constraint object is a property of pyasn1 type. Like TagSet property,
 associated with every pyasn1 type, constraints can never be modified
 in place. The only way to modify pyasn1 type constraint is to associate
 new constraint object to a new pyasn1 type object.
 </p>

 <p>
 A handful of different flavors of <i>constraints</i> are defined in ASN.1.
 We will discuss them one by one in the following chapters and also explain
 how to combine and apply them to types.
 </p>

 <a name="1.4.1"></a>
 <h4>
 1.4.1 Single value constraint
 </h4>

 <p>
 This kind of constraint allows for limiting type to a finite, specified set
 of values.
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 DialButton ::= OCTET STRING (
   "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
 )
 </pre>
 </td></tr></table>

 <p>
 Its pyasn1 implementation would look like:
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 >>> from pyasn1.type import constraint
 >>> c = constraint.SingleValueConstraint(
   '0','1','2','3','4','5','6','7','8','9'
 )
 >>> c
 SingleValueConstraint(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
 >>> c('0')
 >>> c('A')
 Traceback (most recent call last):
 ...
 pyasn1.type.error.ValueConstraintError:
   SingleValueConstraint(0, 1, 2, 3, 4, 5, 6, 7, 8, 9) failed at: A
 >>>
 </pre>
 </td></tr></table>

 <p>
 As can be seen in the snippet above, if a value violates the constraint, an
 exception will be thrown. A constrainted pyasn1 type object holds a
 reference to a constraint object (or their combination, as will be explained
 later) and calls it for value verification.
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 >>> from pyasn1.type import univ, constraint
 >>> class DialButton(univ.OctetString):
 ...   subtypeSpec = constraint.SingleValueConstraint(
 ...       '0','1','2','3','4','5','6','7','8','9'
 ...   )
 >>> DialButton('0')
 DialButton(b'0')
 >>> DialButton('A')
 Traceback (most recent call last):
 ...
 pyasn1.type.error.ValueConstraintError:
   SingleValueConstraint(0, 1, 2, 3, 4, 5, 6, 7, 8, 9) failed at: A
 >>>
 </pre>
 </td></tr></table>

 <p>
 Constrained pyasn1 value object can never hold a violating value.
 </p>

 <a name="1.4.2"></a>
 <h4>
 1.4.2 Value range constraint
 </h4>

 <p>
 A pair of values, compliant to a type to be constrained, denote low and upper
 bounds of allowed range of values of a type.
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 Teenagers ::= INTEGER (13..19)
 </pre>
 </td></tr></table>

 <p>
 And in pyasn1 terms:
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 >>> from pyasn1.type import univ, constraint
 >>> class Teenagers(univ.Integer):
 ...   subtypeSpec = constraint.ValueRangeConstraint(13, 19)
 >>> Teenagers(14)
 Teenagers(14)
 >>> Teenagers(20)
 Traceback (most recent call last):
 ...
 pyasn1.type.error.ValueConstraintError:
   ValueRangeConstraint(13, 19) failed at: 20
 >>>
 </pre>
 </td></tr></table>

 <p>
 Value range constraint usually applies numeric types.
 </p>

 <a name="1.4.3"></a>
 <h4>
 1.4.3 Size constraint
 </h4>

 <p>
 It is sometimes convenient to set or limit the allowed size of a data item
 to be sent from one application to another to manage bandwidth and memory
 consumption issues. Size constraint specifies the lower and upper bounds
 of the size of a valid value.
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 TwoBits ::= BIT STRING (SIZE (2))
 </pre>
 </td></tr></table>

 <p>
 Express the same grammar in pyasn1:
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 >>> from pyasn1.type import univ, constraint
 >>> class TwoBits(univ.BitString):
 ...   subtypeSpec = constraint.ValueSizeConstraint(2, 2)
 >>> TwoBits((1,1))
 TwoBits("'11'B")
 >>> TwoBits((1,1,0))
 Traceback (most recent call last):
 ...
 pyasn1.type.error.ValueConstraintError:
   ValueSizeConstraint(2, 2) failed at: (1, 1, 0)
 >>>
 </pre>
 </td></tr></table>

 <p>
 Size constraint can be applied to potentially massive values - bit or octet
 strings, SEQUENCE OF/SET OF values.
 </p>

 <a name="1.4.4"></a>
 <h4>
 1.4.4 Alphabet constraint
 </h4>

 <p>
 The permitted alphabet constraint is similar to Single value constraint
 but constraint applies to individual characters of a value.
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 MorseCode ::= PrintableString (FROM ("."|"-"|" "))
 </pre>
 </td></tr></table>

 <p>
 And in pyasn1:
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 >>> from pyasn1.type import char, constraint
 >>> class MorseCode(char.PrintableString):
 ...   subtypeSpec = constraint.PermittedAlphabetConstraint(".", "-", " ")
 >>> MorseCode("...---...")
 MorseCode('...---...')
 >>> MorseCode("?")
 Traceback (most recent call last):
 ...
 pyasn1.type.error.ValueConstraintError:
   PermittedAlphabetConstraint(".", "-", " ") failed at: "?"
 >>>
 </pre>
 </td></tr></table>

 <p>
 Current implementation does not handle ranges of characters in constraint
 (FROM "A".."Z" syntax), one has to list the whole set in a range.
 </p>

 <a name="1.4.5"></a>
 <h4>
 1.4.5 Constraint combinations
 </h4>

 <p>
 Up to this moment, we used a single constraint per ASN.1 type. The standard,
 however, allows for combining multiple individual constraints into
 intersections, unions and exclusions.
 </p>

 <p>
 In pyasn1 data model, all of these methods of constraint combinations are
 implemented as constraint-like objects holding individual constraint (or
 combination) objects. Like terminal constraint objects, combination objects
 are capable to perform value verification at its set of enclosed constraints
 according to the logic of particular combination.
 </p>

 <p>
 Constraints intersection verification succeeds only if a value is
 compliant to each constraint in a set. To begin with, the following
 specification will constitute a valid telephone number:
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 PhoneNumber ::= NumericString (FROM ("0".."9")) (SIZE 11)
 </pre>
 </td></tr></table>

 <p>
 Constraint intersection object serves the logic above:
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 >>> from pyasn1.type import char, constraint
 >>> class PhoneNumber(char.NumericString):
 ...   subtypeSpec = constraint.ConstraintsIntersection(
 ...     constraint.PermittedAlphabetConstraint('0','1','2','3','4','5','6','7','8','9'),
 ...     constraint.ValueSizeConstraint(11, 11)
 ...   )
 >>> PhoneNumber('79039343212')
 PhoneNumber('79039343212')
 >>> PhoneNumber('?9039343212')
 Traceback (most recent call last):
 ...
 pyasn1.type.error.ValueConstraintError:
   ConstraintsIntersection(
     PermittedAlphabetConstraint('0','1','2','3','4','5','6','7','8','9'),
       ValueSizeConstraint(11, 11)) failed at:
    PermittedAlphabetConstraint('0','1','2','3','4','5','6','7','8','9') failed at: "?039343212"
 >>> PhoneNumber('9343212')
 Traceback (most recent call last):
 ...
 pyasn1.type.error.ValueConstraintError:
   ConstraintsIntersection(
     PermittedAlphabetConstraint('0','1','2','3','4','5','6','7','8','9'),
       ValueSizeConstraint(11, 11)) failed at:
   ValueSizeConstraint(10, 10) failed at: "9343212"
 >>>
 </pre>
 </td></tr></table>

 <p>
 Union of constraints works by making sure that a value is compliant
 to any of the constraint in a set. For instance:
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 CapitalOrSmall ::= IA5String (FROM ('A','B','C') | FROM ('a','b','c'))
 </pre>
 </td></tr></table>

 <p>
 It's important to note, that a value must fully comply to any single
 constraint in a set. In the specification above, a value of all small or
 all capital letters is compliant, but a mix of small&capitals is not.
 Here's its pyasn1 analogue:
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 >>> from pyasn1.type import char, constraint
 >>> class CapitalOrSmall(char.IA5String):
 ...   subtypeSpec = constraint.ConstraintsUnion(
 ...     constraint.PermittedAlphabetConstraint('A','B','C'),
 ...     constraint.PermittedAlphabetConstraint('a','b','c')
 ...   )
 >>> CapitalOrSmall('ABBA')
 CapitalOrSmall('ABBA')
 >>> CapitalOrSmall('abba')
 CapitalOrSmall('abba')
 >>> CapitalOrSmall('Abba')
 Traceback (most recent call last):
 ...
 pyasn1.type.error.ValueConstraintError:
   ConstraintsUnion(PermittedAlphabetConstraint('A', 'B', 'C'),
     PermittedAlphabetConstraint('a', 'b', 'c')) failed at: failed for "Abba"
 >>>
 </pre>
 </td></tr></table>

 <p>
 Finally, the exclusion constraint simply negates the logic of value
 verification at a constraint. In the following example, any integer value
 is allowed in a type but not zero.
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 NoZero ::= INTEGER (ALL EXCEPT 0)
 </pre>
 </td></tr></table>

 <p>
 In pyasn1 the above definition would read:
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 >>> from pyasn1.type import univ, constraint
 >>> class NoZero(univ.Integer):
 ...   subtypeSpec = constraint.ConstraintsExclusion(
 ...     constraint.SingleValueConstraint(0)
 ...   )
 >>> NoZero(1)
 NoZero(1)
 >>> NoZero(0)
 Traceback (most recent call last):
 ...
 pyasn1.type.error.ValueConstraintError:
   ConstraintsExclusion(SingleValueConstraint(0)) failed at: 0
 >>>
 </pre>
 </td></tr></table>

 <p>
 The depth of such a constraints tree, built with constraint combination objects
 at its nodes, has not explicit limit. Value verification is performed in a
 recursive manner till a definite solution is found.
 </p>

 <a name="1.5"></a>
 <h4>
 1.5 Types relationships
 </h4>

 <p>
 In the course of data processing in an application, it is sometimes
 convenient to figure out the type relationships between pyasn1 type or
 value objects. Formally, two things influence pyasn1 types relationship:
 <i>tag set</i> and <i>subtype constraints</i>. One pyasn1 type is considered
 to be a derivative of another if their TagSet and Constraint objects are
 a derivation of one another.
 </p>

 <p>
 The following example illustrates the concept (we use the same tagset but
 different constraints for simplicity):
 </p>

 <table bgcolor="lightgray" border=0 width=100%><TR><TD>
 <pre>
 >>> from pyasn1.type import univ, constraint
 >>> i1 = univ.Integer(subtypeSpec=constraint.ValueRangeConstraint(3,8))
 >>> i2 = univ.Integer(subtypeSpec=constraint.ConstraintsIntersection(
 ...    constraint.ValueRangeConstraint(3,8),
 ...    constraint.ValueRangeConstraint(4,7)
 ... ) )
 >>> i1.isSameTypeWith(i2)
 False
 >>> i1.isSuperTypeOf(i2)
 True
 >>> i1.isSuperTypeOf(i1)
 True
 >>> i2.isSuperTypeOf(i1)
 False
 >>>
 </pre>
 </td></tr></table>

 <p>
 As can be seen in the above code snippet, there are two methods of any pyasn1
 type/value object that test types for their relationship:
 <b>isSameTypeWith</b>() and <b>isSuperTypeOf</b>(). The former is
 self-descriptive while the latter yields true if the argument appears
 to be a pyasn1 object which has tagset and constraints derived from those
 of the object being called.
 </p>

 <hr>

 </td>
 </tr>
 </table>
 </center>
 </body>
 </html>
	<html>
	<title>
	PyASN1 subtype constraints
	</title>
	<head>
	</head>
	<body>
	<center>
	<table width=60%>
	<tr>
	<td>

	<h4>
	1.4 PyASN1 subtype constraints
	</h4>

	<p>
	Most ASN.1 types can correspond to an infinite set of values. To adapt to
	particular application's data model and needs, ASN.1 provides a mechanism
	for limiting the infinite set to values, that make sense in particular case.
	</p>

	<p>
	Imposing value constraints on an ASN.1 type can also be seen as creating
	a subtype from its base type.
	</p>

	<p>
	In pyasn1, constraints take shape of immutable objects capable
	of evaluating given value against constraint-specific requirements.
	Constraint object is a property of pyasn1 type. Like TagSet property,
	associated with every pyasn1 type, constraints can never be modified
	in place. The only way to modify pyasn1 type constraint is to associate
	new constraint object to a new pyasn1 type object.
	</p>

	<p>
	A handful of different flavors of <i>constraints</i> are defined in ASN.1.
	We will discuss them one by one in the following chapters and also explain
	how to combine and apply them to types.
	</p>

	<a name="1.4.1"></a>
	<h4>
	1.4.1 Single value constraint
	</h4>

	<p>
	This kind of constraint allows for limiting type to a finite, specified set
	of values.
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	DialButton ::= OCTET STRING (
	"0" \| "1" \| "2" \| "3" \| "4" \| "5" \| "6" \| "7" \| "8" \| "9"
	)
	</pre>
	</td></tr></table>

	<p>
	Its pyasn1 implementation would look like:
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	>>> from pyasn1.type import constraint
	>>> c = constraint.SingleValueConstraint(
	'0','1','2','3','4','5','6','7','8','9'
	)
	>>> c
	SingleValueConstraint(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
	>>> c('0')
	>>> c('A')
	Traceback (most recent call last):
	...
	pyasn1.type.error.ValueConstraintError:
	SingleValueConstraint(0, 1, 2, 3, 4, 5, 6, 7, 8, 9) failed at: A
	>>>
	</pre>
	</td></tr></table>

	<p>
	As can be seen in the snippet above, if a value violates the constraint, an
	exception will be thrown. A constrainted pyasn1 type object holds a
	reference to a constraint object (or their combination, as will be explained
	later) and calls it for value verification.
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	>>> from pyasn1.type import univ, constraint
	>>> class DialButton(univ.OctetString):
	... subtypeSpec = constraint.SingleValueConstraint(
	... '0','1','2','3','4','5','6','7','8','9'
	... )
	>>> DialButton('0')
	DialButton(b'0')
	>>> DialButton('A')
	Traceback (most recent call last):
	...
	pyasn1.type.error.ValueConstraintError:
	SingleValueConstraint(0, 1, 2, 3, 4, 5, 6, 7, 8, 9) failed at: A
	>>>
	</pre>
	</td></tr></table>

	<p>
	Constrained pyasn1 value object can never hold a violating value.
	</p>

	<a name="1.4.2"></a>
	<h4>
	1.4.2 Value range constraint
	</h4>

	<p>
	A pair of values, compliant to a type to be constrained, denote low and upper
	bounds of allowed range of values of a type.
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	Teenagers ::= INTEGER (13..19)
	</pre>
	</td></tr></table>

	<p>
	And in pyasn1 terms:
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	>>> from pyasn1.type import univ, constraint
	>>> class Teenagers(univ.Integer):
	... subtypeSpec = constraint.ValueRangeConstraint(13, 19)
	>>> Teenagers(14)
	Teenagers(14)
	>>> Teenagers(20)
	Traceback (most recent call last):
	...
	pyasn1.type.error.ValueConstraintError:
	ValueRangeConstraint(13, 19) failed at: 20
	>>>
	</pre>
	</td></tr></table>

	<p>
	Value range constraint usually applies numeric types.
	</p>

	<a name="1.4.3"></a>
	<h4>
	1.4.3 Size constraint
	</h4>

	<p>
	It is sometimes convenient to set or limit the allowed size of a data item
	to be sent from one application to another to manage bandwidth and memory
	consumption issues. Size constraint specifies the lower and upper bounds
	of the size of a valid value.
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	TwoBits ::= BIT STRING (SIZE (2))
	</pre>
	</td></tr></table>

	<p>
	Express the same grammar in pyasn1:
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	>>> from pyasn1.type import univ, constraint
	>>> class TwoBits(univ.BitString):
	... subtypeSpec = constraint.ValueSizeConstraint(2, 2)
	>>> TwoBits((1,1))
	TwoBits("'11'B")
	>>> TwoBits((1,1,0))
	Traceback (most recent call last):
	...
	pyasn1.type.error.ValueConstraintError:
	ValueSizeConstraint(2, 2) failed at: (1, 1, 0)
	>>>
	</pre>
	</td></tr></table>

	<p>
	Size constraint can be applied to potentially massive values - bit or octet
	strings, SEQUENCE OF/SET OF values.
	</p>

	<a name="1.4.4"></a>
	<h4>
	1.4.4 Alphabet constraint
	</h4>

	<p>
	The permitted alphabet constraint is similar to Single value constraint
	but constraint applies to individual characters of a value.
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	MorseCode ::= PrintableString (FROM ("."\|"-"\|" "))
	</pre>
	</td></tr></table>

	<p>
	And in pyasn1:
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	>>> from pyasn1.type import char, constraint
	>>> class MorseCode(char.PrintableString):
	... subtypeSpec = constraint.PermittedAlphabetConstraint(".", "-", " ")
	>>> MorseCode("...---...")
	MorseCode('...---...')
	>>> MorseCode("?")
	Traceback (most recent call last):
	...
	pyasn1.type.error.ValueConstraintError:
	PermittedAlphabetConstraint(".", "-", " ") failed at: "?"
	>>>
	</pre>
	</td></tr></table>

	<p>
	Current implementation does not handle ranges of characters in constraint
	(FROM "A".."Z" syntax), one has to list the whole set in a range.
	</p>

	<a name="1.4.5"></a>
	<h4>
	1.4.5 Constraint combinations
	</h4>

	<p>
	Up to this moment, we used a single constraint per ASN.1 type. The standard,
	however, allows for combining multiple individual constraints into
	intersections, unions and exclusions.
	</p>

	<p>
	In pyasn1 data model, all of these methods of constraint combinations are
	implemented as constraint-like objects holding individual constraint (or
	combination) objects. Like terminal constraint objects, combination objects
	are capable to perform value verification at its set of enclosed constraints
	according to the logic of particular combination.
	</p>

	<p>
	Constraints intersection verification succeeds only if a value is
	compliant to each constraint in a set. To begin with, the following
	specification will constitute a valid telephone number:
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	PhoneNumber ::= NumericString (FROM ("0".."9")) (SIZE 11)
	</pre>
	</td></tr></table>

	<p>
	Constraint intersection object serves the logic above:
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	>>> from pyasn1.type import char, constraint
	>>> class PhoneNumber(char.NumericString):
	... subtypeSpec = constraint.ConstraintsIntersection(
	... constraint.PermittedAlphabetConstraint('0','1','2','3','4','5','6','7','8','9'),
	... constraint.ValueSizeConstraint(11, 11)
	... )
	>>> PhoneNumber('79039343212')
	PhoneNumber('79039343212')
	>>> PhoneNumber('?9039343212')
	Traceback (most recent call last):
	...
	pyasn1.type.error.ValueConstraintError:
	ConstraintsIntersection(
	PermittedAlphabetConstraint('0','1','2','3','4','5','6','7','8','9'),
	ValueSizeConstraint(11, 11)) failed at:
	PermittedAlphabetConstraint('0','1','2','3','4','5','6','7','8','9') failed at: "?039343212"
	>>> PhoneNumber('9343212')
	Traceback (most recent call last):
	...
	pyasn1.type.error.ValueConstraintError:
	ConstraintsIntersection(
	PermittedAlphabetConstraint('0','1','2','3','4','5','6','7','8','9'),
	ValueSizeConstraint(11, 11)) failed at:
	ValueSizeConstraint(10, 10) failed at: "9343212"
	>>>
	</pre>
	</td></tr></table>

	<p>
	Union of constraints works by making sure that a value is compliant
	to any of the constraint in a set. For instance:
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	CapitalOrSmall ::= IA5String (FROM ('A','B','C') \| FROM ('a','b','c'))
	</pre>
	</td></tr></table>

	<p>
	It's important to note, that a value must fully comply to any single
	constraint in a set. In the specification above, a value of all small or
	all capital letters is compliant, but a mix of small&capitals is not.
	Here's its pyasn1 analogue:
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	>>> from pyasn1.type import char, constraint
	>>> class CapitalOrSmall(char.IA5String):
	... subtypeSpec = constraint.ConstraintsUnion(
	... constraint.PermittedAlphabetConstraint('A','B','C'),
	... constraint.PermittedAlphabetConstraint('a','b','c')
	... )
	>>> CapitalOrSmall('ABBA')
	CapitalOrSmall('ABBA')
	>>> CapitalOrSmall('abba')
	CapitalOrSmall('abba')
	>>> CapitalOrSmall('Abba')
	Traceback (most recent call last):
	...
	pyasn1.type.error.ValueConstraintError:
	ConstraintsUnion(PermittedAlphabetConstraint('A', 'B', 'C'),
	PermittedAlphabetConstraint('a', 'b', 'c')) failed at: failed for "Abba"
	>>>
	</pre>
	</td></tr></table>

	<p>
	Finally, the exclusion constraint simply negates the logic of value
	verification at a constraint. In the following example, any integer value
	is allowed in a type but not zero.
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	NoZero ::= INTEGER (ALL EXCEPT 0)
	</pre>
	</td></tr></table>

	<p>
	In pyasn1 the above definition would read:
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	>>> from pyasn1.type import univ, constraint
	>>> class NoZero(univ.Integer):
	... subtypeSpec = constraint.ConstraintsExclusion(
	... constraint.SingleValueConstraint(0)
	... )
	>>> NoZero(1)
	NoZero(1)
	>>> NoZero(0)
	Traceback (most recent call last):
	...
	pyasn1.type.error.ValueConstraintError:
	ConstraintsExclusion(SingleValueConstraint(0)) failed at: 0
	>>>
	</pre>
	</td></tr></table>

	<p>
	The depth of such a constraints tree, built with constraint combination objects
	at its nodes, has not explicit limit. Value verification is performed in a
	recursive manner till a definite solution is found.
	</p>

	<a name="1.5"></a>
	<h4>
	1.5 Types relationships
	</h4>

	<p>
	In the course of data processing in an application, it is sometimes
	convenient to figure out the type relationships between pyasn1 type or
	value objects. Formally, two things influence pyasn1 types relationship:
	<i>tag set</i> and <i>subtype constraints</i>. One pyasn1 type is considered
	to be a derivative of another if their TagSet and Constraint objects are
	a derivation of one another.
	</p>

	<p>
	The following example illustrates the concept (we use the same tagset but
	different constraints for simplicity):
	</p>

	<table bgcolor="lightgray" border=0 width=100%><TR><TD>
	<pre>
	>>> from pyasn1.type import univ, constraint
	>>> i1 = univ.Integer(subtypeSpec=constraint.ValueRangeConstraint(3,8))
	>>> i2 = univ.Integer(subtypeSpec=constraint.ConstraintsIntersection(
	... constraint.ValueRangeConstraint(3,8),
	... constraint.ValueRangeConstraint(4,7)
	... ) )
	>>> i1.isSameTypeWith(i2)
	False
	>>> i1.isSuperTypeOf(i2)
	True
	>>> i1.isSuperTypeOf(i1)
	True
	>>> i2.isSuperTypeOf(i1)
	False
	>>>
	</pre>
	</td></tr></table>

	<p>
	As can be seen in the above code snippet, there are two methods of any pyasn1
	type/value object that test types for their relationship:
	<b>isSameTypeWith</b>() and <b>isSuperTypeOf</b>(). The former is
	self-descriptive while the latter yields true if the argument appears
	to be a pyasn1 object which has tagset and constraints derived from those
	of the object being called.
	</p>

	<hr>

	</td>
	</tr>
	</table>
	</center>
	</body>
	</html>