Typing system for places (and transitions guards). Types are contraint checkers to verify whether a value is in the type or not. For instance:

>>> 5 in tInteger
True
>>> 4.3 in tInteger
False

The typechecking of several values is possible using the type as a function. It fails if one value is not in the type.

>>> tInteger(5, 4, 6)
True
>>> tInteger(5, 4, 6.0)
False

Types can be composed in order to build more complexe types. For example:

>>> 8 in (tInteger & ~Range(1, 5))
True
>>> 3 in (tInteger & ~Range(1, 5))
False

The various compositions are the same as sets operations, plus the complement: &, |, -, ^ and ~ (complement).

Various types are predefined (like tInteger) the others can be constructed using the various classes in the module. Prefefined types are:

• tAll: any value is in the type
• tNothing: empty type
• tString: string values
• tList: lists values
• tInteger: integer values
• tNatural: non-negative integers
• tPositive: strictly positive integers
• tFloat: float values
• tNumber: integers or float values
• tDict: Python's dict values
• tNone: the single value None
• tBoolean: True or False
• tTuple: tuple values
• tPair: tuples of length two

Types with finitely many elements can be iterated over:

>>> list(sorted(iter(CrossProduct(Range(0, 10, 2), tBoolean) & ~OneOf((4, True), (6, False)))))
[(0, False), (0, True), (2, False), (2, True), (4, False), (6, True), (8, False), (8, True)]
>>> list(iter(OneOf(1, 2, 3)))
[1, 2, 3]
>>> iter(tInteger)
Traceback (most recent call last):
...
TypeError: ... not iterable
>>> iter(~OneOf(1, 2, 3))
Traceback (most recent call last):
...
TypeError: ... not iterable

Class Type

class Type (object) :

Base class for all types. Implements operations &, |, -, ^ and ~ to build new types. Also implement the typechecking of several values. All the subclasses should implement the method __contains__ to typecheck a single object.

This class is abstract and should not be instantiated.

Method Type.__and__

def __and__ (self, other) :

Intersection type.

>>> Instance(int) & Greater(0)
(Instance(int) & Greater(0))

Call API

• Type other: the other type in the intersection
• return Type: the intersection of both types

Method Type.__or__

def __or__ (self, other) :

Union type.

>>> Instance(int) | Instance(bool)
(Instance(int) | Instance(bool))

Call API

• Type other: the other type in the union
• return Type: the union of both types

Method Type.__sub__

def __sub__ (self, other) :

Substraction type.

>>> Instance(int) - OneOf([0, 1, 2])
(Instance(int) - OneOf([0, 1, 2]))

Call API

• Type other: the other type in the substraction
• return Type: the type self minus the type other

Method Type.__xor__

def __xor__ (self, other) :

Disjoint union type.

>>> Greater(0) ^ Instance(float)
(Greater(0) ^ Instance(float))

Call API

• Type other: the other type in the disjoint union
• return Type: the disjoint union of both types

Method Type.__invert__

def __invert__ (self) :

Complementary type.

>>> ~ Instance(int)
(~Instance(int))

Call API

• return Type: the complementary type

Method Type.__call__

def __call__ (self, *values) :

Typecheck values.

>>> Instance(int)(3, 4, 5)
True
>>> Instance(int)(3, 4, 5.0)
False

Call API

• object values: values that have to be checked
• return bool: True if all the values are in the types, False otherwise

Class Instance

class Instance (Type) :

A type whose values are all instances of one class.

>>> [1, 2] in Instance(list)
True
>>> (1, 2) in Instance(list)
False

Method Instance.__init__

def __init__ (self, _class) :

Initialize the type

>>> Instance(int)
Instance(int)

Call API

• class _class: the class of instance
• return Instance: initialized object

Class TypeCheck

class TypeCheck (Type) :

A type whose values are accepted by a given function.

>>> def odd (val) :
...     return type(val) is int and (val % 2) == 1
>>> 3 in TypeCheck(odd)
True
>>> 4 in TypeCheck(odd)
False
>>> 3.0 in TypeCheck(odd)
False

Method TypeCheck.__init__

def __init__ (self, checker, iterate=None) :

Initialize the type, optionally, a function to iterate over the elements may be provided.

>>> import operator
>>> TypeCheck(operator.truth)
TypeCheck(...truth)
>>> list(TypeCheck(operator.truth))
Traceback (most recent call last):
  ...
ValueError: type not iterable
>>> def true_values () : # enumerates only choosen values
...     yield True
...     yield 42
...     yield '42'
...     yield [42]
...     yield (42,)
...     yield {True: 42}
>>> TypeCheck(operator.truth, true_values)
TypeCheck(...truth, snakes.typing.true_values)
>>> list(TypeCheck(operator.truth, true_values))
[True, 42, '42', [42], (42,), {True: 42}]

Call API

• callable checker: a function that checks one value and returns True if it is in te type and False otherwise
• generator iterate: None or an iterator over the values of the type

Class OneOf

class OneOf (Type) :

A type whose values are explicitely enumerated.

>>> 3 in OneOf(1, 2, 3, 4, 5)
True
>>> 0 in OneOf(1, 2, 3, 4, 5)
False

Class Collection

class Collection (Type) :

A type whose values are a given container, holding items of a given type and ranging in a given interval.

>>> [0, 1.1, 2, 3.3, 4] in Collection(Instance(list), tNumber, 3, 10)
True
>>> [0, 1.1] in Collection(Instance(list), tNumber, 3, 10) #too short
False
>>> [0, '1.1', 2, 3.3, 4] in Collection(Instance(list), tNumber, 3, 10) #wrong item
False

Method Collection.__init__

def __init__ (self, collection, items, min=None, max=None) :

Initialise the type

>>> Collection(Instance(list), tNumber, 3, 10)
Collection(Instance(list), (Instance(int) | Instance(float)), min=3, max=10)

Call API

• Type collection: the collection type
• Type items: the type of the items
• object min: the smallest allowed value
• object max: the greatest allowed value

Function List

def List (items, min=None, max=None) :

Shorthand for instantiating Collection

>>> List(tNumber, min=3, max=10)
Collection(Instance(list), (Instance(int) | Instance(float)), min=3, max=10)

Call API

• Type items: the type of the elements in the collection
• int min: the minimum number of elements in the collection or None
• int max: the maximum number of elements in the collection or None
• return Collection: a type that checks the given constraints

Function Tuple

def Tuple (items, min=None, max=None) :

Shorthand for instantiating Collection

>>> Tuple(tNumber, min=3, max=10)
Collection(Instance(tuple), (Instance(int) | Instance(float)), min=3, max=10)

Call API

• Type items: the type of the elements in the collection
• int min: the minimum number of elements in the collection or None
• int max: the maximum number of elements in the collection or None
• return Collection: a type that checks the given constraints

Function Set

def Set (items, min=None, max=None) :

Shorthand for instantiating Collection

>>> Set(tNumber, min=3, max=10)
Collection(Instance(set), (Instance(int) | Instance(float)), min=3, max=10)

Call API

• Type items: the type of the elements in the collection
• int min: the minimum number of elements in the collection or None
• int max: the maximum number of elements in the collection or None
• return Collection: a type that checks the given constraints

Class Mapping

class Mapping (Type) :

A type whose values are mapping (eg, dict)

>>> {'Yes': True, 'No': False} in Mapping(tString, tAll)
True
>>> {True: 1, False: 0} in Mapping(tString, tAll)
False

Method Mapping.__init__

def __init__ (self, keys, items, _dict=Instance(dict)) :

Initialise a mapping type

>>> Mapping(tInteger, tFloat)
Mapping(Instance(int), Instance(float), Instance(dict))
>>> from snakes.data import hdict
>>> Mapping(tInteger, tFloat, Instance(hdict))
Mapping(Instance(int), Instance(float), Instance(hdict))

Call API

• Type keys: the type for the keys
• Type items: the type for the items
• dict _dict: the class that mapping must be instances of

Class Range

class Range (Type) :

A type whose values are in a given range

Notice that ranges are not built into the memory so that huge values can be used.

>>> 3 in Range(1, 2**128, 2)
True
>>> 4 in Range(1, 2**128, 2)
False

Method Range.__init__

def __init__ (self, first, last, step=1) :

The values are those that the builtin range(first, last, step) would return.

>>> Range(1, 10)
Range(1, 10)
>>> Range(1, 10, 2)
Range(1, 10, 2)

Call API

• int first: first element in the range
• int last: upper bound of the range, not belonging to it
• int step: step between elements in the range

Class Greater

class Greater (Type) :

A type whose values are greater than a minimum.

The minimum and the checked values can be of any type as soon as they can be compared with >.

>>> 6 in Greater(3)
True
>>> 3 in Greater(3)
False

Method Greater.__init__

def __init__ (self, min) :

Initialises the type

>>> Greater(5)
Greater(5)

Call API

• object min: the greatest value not included in the type

Class GreaterOrEqual

class GreaterOrEqual (Type) :

A type whose values are greater or equal than a minimum.

See the description of Greater

Method GreaterOrEqual.__init__

def __init__ (self, min) :

Initialises the type

>>> GreaterOrEqual(5)
GreaterOrEqual(5)

Call API

• object min: the minimal allowed value

Class Less

class Less (Type) :

A type whose values are less than a maximum.

See the description of Greater

Method Less.__init__

def __init__ (self, max) :

Initialises the type

>>> Less(5)
Less(5)

Call API

• object max

Class LessOrEqual

class LessOrEqual (Type) :

A type whose values are less than or equal to a maximum.

See the description of Greater

Method LessOrEqual.__init__

def __init__ (self, max) :

Initialises the type

>>> LessOrEqual(5)
LessOrEqual(5)

Call API

• object max

Class CrossProduct

class CrossProduct (Type) :

A type whose values are tuples, each component of them being in given types. The resulting type is the cartesian cross product of the compound types.

>>> (1, 3, 5) in CrossProduct(Range(1, 10), Range(1, 10, 2), Range(1, 10))
True
>>> (2, 4, 6) in CrossProduct(Range(1, 10), Range(1, 10, 2), Range(1, 10))
False

Method CrossProduct.__init__

def __init__ (self, *types) :

Initialise the type

>>> CrossProduct(Instance(int), Instance(float))
CrossProduct(Instance(int), Instance(float))

Call API

• Type types: the types of each component of the allowed tuples