Type-safe versions of Python's builtin iterables
Project description
TypedIter
The Type-Safe Versions of Python Built-in Iterables
This package aims to provide type-safe versions of some python built-in iterables ( list
, tuple
, set
, frozenset
), those can be used exactly in the same way as their built-in equivalents, except that a type of item is provided at instance creation (i_type
), and breaking that type restriction will raise a custom TypeRestrictionError
.
(The type-checking is executed at runtime.)
Two Flavours of Type Safety
For each built-in iterable, this package provides 2 type-safe versions.
Built-in class | Light version | Complete version |
---|---|---|
list |
TypedList_lt |
TypedList |
tuple |
TypedTuple_lt |
TypedTuple |
set |
TypedSet_lt |
TypedSet |
frozenset |
TypedFrozenset_lt |
TypedFrozenset |
Note: The 'complete' versions inherits from their 'light' version equivalents.
Light
The "light" version (class name ending in _lt) only ensures the type safety of the current instance.
- Mutating methods that could insert incompatible items are overridden, they perform type checks, and will fail instead of inserting an incompatible item.
- Non-Mutating methods are all handled by the built-in class the typed iterable is based on.
So for example, a
TypedList_lt
addition, is not type-checked, and will return a built-inlist
. The only exception being thecopy()
method, which is overridden to return a new instance of the current typed iterable class.
The aim is to provide type safety for the current instance only, while avoiding slowing down operations that don't directly affect it. This makes those operations faster, and more permissive, but their results are downgraded to built-in iterables.
Complete
The "complete" version ensures the type safety of the current instance, and type safety of new instances generated from it.
- Mutating methods that could insert incompatible items are overridden, they perform type checks, and will fail instead of inserting an incompatible item.
- Non-Mutating methods that used to return an instance of the same class are overridden to return an instance of the current typed iterable, for example,
list
addition returns a newlist
, soTypedList
addition returns a newTypedList
. So those operations will perform type checks and fail instead of inserting an incompatible item in the operation result.
The aim is to be coherent with the built-in iterables the classes are based on. The downside is that it makes those operations heavier and less permissive.
Installation
pip install typediter
Instance Creation
from typediter import (
TypedList,
TypedSet,
)
# Creating a list that allows only int items
# -> Any iterable can be used as initialisation value
int_list = TypedList( (1, 2, 3), i_type=int )
# Creating an empty set that allows only str items
# -> Without initialisation value, we create an empty iterable
str_set = TypedSet( i_type=str )
- If one of the given items isn't an instance of the expected
i_type
the initialisation will fail withTypeRestrictionError
. - If a non-iterable initial value is given, the initialisation will fail with
IterableExpectedError
. - If
i_type
is not an instance oftype
, the initialisation will fail with anInvalidTypeRestrictionError
. - For
set
/frozenset
based classes, ifi_type
is not a hashable type, the initialisation will fail with anInvalidTypeRestrictionError
.
Operations
All operations and methods defined in the built-in version are supported, and can be used in the same way.
Mutating Operations
For both 'light' and 'complete' versions, any operation directly modifying the instance, that could insert an incompatible item is type-checked.
from typediter import (
TypedList,
TypedSet,
)
# Creating type-restricted iterables
int_list = TypedList( (1, 2, 3), i_type=int )
int_set = TypedSet( (1, 2, 3), i_type=int )
# Same operations and methods as the built-in equivalent
int_list.append( 4 )
int_list[2] = 42
print( int_list ) # -> List[int]:[1, 2, 42, 4]
int_set.add( 4 )
int_set.update({ 5, 6 })
print( int_set ) # -> Set[int]:{1, 2, 3, 4, 5, 6}
- Trying to insert an incompatible item will fail with
TypeRestrictionError
. - Type-checked operations expecting an iterable, but called with something else, will fail with
IterableExpectedError
. - Exceptions that are usually raised for a given operation (such as
TypeError
) can still be raised by the underlying built-in class.
Non-mutating operations: Light vs Complete versions
Operations that return a new instance and don't directly affect the current instance are handled differently between the 'light' and 'complete' versions of typed iterables:
- light versions: all non-mutating operations are handled by the base built-in iterable (except
copy()
which is overridden to return a new instance of the current typed iterable class). - complete versions: non-mutating operations that return a new instance of the same class are overridden to return a new instance of the current typed iterable (for example,
list
addition returns a newlist
, soTypedList
addition returns a newTypedList
)
# Importing both 'complete' and 'light' versions of typed list
from typediter import TypedList_lt, TypedList
# Creating instances
light_str_list = TypedList_lt( ('A', 'B', 'C'), i_type=str )
complete_str_list = TypedList( ('A', 'B', 'C'), i_type=str )
# Operation handled by the light version:
# (Not type-restricted, returns a new built-in list)
light_result = light_str_list + [ 1, 2, 3 ]
type( light_result ) # -> list
# Operation handled by the complete version:
# (Type-restricted, returns a new typed iterable)
complete_result = complete_str_list + [ 'D', 'E', 'F' ]
type( complete_result ) # -> TypedList
complete_result = complete_str_list + [ 1, 2, 3 ] # -> Fails with TypeRestrictionError
for both versions:
- Type-checked operations expecting an iterable, but called with something else, will fail with
IterableExpectedError
. - Exceptions that are usually raised for a given operation (such as
TypeError
) can still be raised by the underlying built-in class.
for the complete version:
- Trying to insert an incompatible item in the resulting instance will fail with
TypeRestrictionError
. - Order matters in operations using operators ( + - ^ | ...), the first object has priority to handle the operation, if the 'complete' typed iterable is not first, the operation will be handled by the other object and type safety isn't enforced, for example:
[1,2,3]+complete_str_list
will return a built-in list and will not fail. - Operations are type-restricted only if the operation is about to introduce an incompatible item in the result, operations that cannot introduce an item of the wrong type in the result aren't checked at all (like
set
difference()
method).
Utility Functions
All utility functions can be imported from typediter.utils
from typediter.utils import get_converter_func
get_converter_func( typed_iterable_cls, *, i_type )
Returns a function converting an iterable to an instance of the given typed iterable class, restricted to the specified type (i_type
).
Remark: if we create a converter for something else than a typed iterable class, or with an invalid i_type
, it will only fail when trying to convert a value, not when creating the converter.
from typediter import TypedList
from typediter.utils import get_converter_func
# Getting a function converting an iterable to a TypedList[str]
to_str_list = get_converter_func( TypedList, i_type=str )
# Converting an iterable to a typed list
str_list = to_str_list( ['A', 'B', 'C'] )
type( str_list ) # -> TypedList
- The converter getter function is only meant to be used with typed iterable classes.
- If the iterable we are trying to convert, contains items that are not instances of
i_type
, the conversion will fail withTypeRestrictionError
. - If the value being converted is not an iterable, the conversion will fail with
IterableExpectedError
. - If
i_type
is not an instance oftype
, the conversion will fail with anInvalidTypeRestrictionError
. - When converting to
set
/frozenset
based classes, ifi_type
is not a hashable type, the conversion will fail with anInvalidTypeRestrictionError
.
get_typesafe_tuple_converter_func( i_type )
Returns a function converting an iterable to a built-in tuple
, restricted to the specified type (i_type
).
Remark: if we create a converter with an invalid i_type
, it will only fail when trying to convert a value, not when creating the converter.
from typediter.utils import get_typesafe_tuple_converter_func
# Getting the converter functions
to_str_builtin_tuple = get_typesafe_tuple_converter_func( str )
# Converting iterables to type-safe tuple
str_builtin_tuple = to_str_builtin_tuple( ['A', 'B', 'C'] )
type( str_builtin_tuple ) # -> tuple
- If the iterable we are trying to convert, contains items that are not instances of
i_type
, the conversion will fail withTypeRestrictionError
. - If the value being converted is not an iterable, the conversion will fail with
IterableExpectedError
. - If
i_type
is not an instance oftype
, the conversion will fail with anInvalidTypeRestrictionError
.
get_typesafe_frozenset_converter_func( i_type )
Returns a function converting an iterable to a built-in frozenset
, restricted to the specified type (i_type
).
Remark: if we create a converter with an invalid i_type
, it will only fail when trying to convert a value, not when creating the converter.
from typediter.utils import get_typesafe_frozenset_converter_func
# Getting the converter functions
to_str_builtin_frozenset = get_typesafe_frozenset_converter_func( str )
# Converting iterables to type-safe frozenset
str_builtin_frozenset = to_str_builtin_frozenset( ['A', 'B', 'C'] )
type( str_builtin_frozenset ) # -> frozenset
- If the iterable we are trying to convert, contains items that are not instances of
i_type
, the conversion will fail withTypeRestrictionError
. - If the value being converted is not an iterable, the conversion will fail with
IterableExpectedError
. - If
i_type
is not an instance oftype
or if it's not a hashable type, the conversion will fail with anInvalidTypeRestrictionError
.
filter_items( items, *, i_type )
Function taking an iterable and a type, and returning a tuple containing only the items that are instances of that type.
from typediter.utils import filter_items
filtered_items = filter_items( [1, 'A', 2, 'B'], i_type=int )
print( filtered_items ) # -> ( 1, 2 )
is_typediter_instance( obj )
Function returning True if the given argument is an instance of a typed iterable
from typediter import TypedList, TypedTuple
from typediter.utils import is_typediter_instance
# Creating typed iterable instances
str_list = TypedList( ('A', 'B', 'C'), i_type=str )
str_tuple = TypedTuple( ('A', 'B', 'C'), i_type=str )
is_typediter_instance( str_list ) # -> True
is_typediter_instance( str_tuple ) # -> True
is_typediter_instance( TypedList ) # -> False
is_typediter_instance( ['A', 'B', 'C'] ) # -> False
is_typediter_subclass( cls )
Function returning True if the given argument is a typed iterable class
from typediter import TypedList, TypedTuple
from typediter.utils import is_typediter_subclass
is_typediter_subclass( TypedList ) # -> True
is_typediter_subclass( TypedTuple ) # -> True
is_typediter_subclass( list ) # -> False
Custom Exceptions
All exceptions can be imported from typediter.exceptions
.
from typediter.exceptions import TypeRestrictionError
TypeRestrictionError
Inherits from Exception
Exception raised to prevent operations from breaking type restriction.
OperationError
Inherits from Exception
Base exception for errors related to mishandled type-checked operations.
InvalidTypeRestrictionError
Inherits from OperationError
Exception raised if the type restriction (i_type
) is invalid.
Either because it's not a type,
or because the type restriction is applied to a set
/frozenset
based class
and the provided i_type
is not hashable.
IterableExpectedError
Inherits from OperationError
Exception raised when a type-checked operation expecting an iterable instance receives something else.
Type hinting utils
Some utility types are made available for type hinting and can be imported from typediter.types
from typediter.types import TypedIterable_T
foo: TypedIterable_T = ...
bar: TypedIterable_T[str] = ...
TypedIterable_T
Any instance of a typed iterable class:
TypedList_lt
/TypedList
TypedTuple_lt
/TypedTuple
TypedSet_lt
/TypedSet
TypedFrozenset_lt
/TypedFrozenset
MutableTypedIterable_T
An instance of a mutable typed iterable class:
TypedList_lt
/TypedList
TypedSet_lt
/TypedSet
FrozenTypedIterable_T
An instance of an immutable typed iterable class:
TypedTuple_lt
/TypedTuple
TypedFrozenset_lt
/TypedFrozenset
Tests
This package was tested with python 3.11.2, 3.11.9 and 3.12.5, on Debian 12.
It won't work with any version below 3.11.
Running Tests
- Download the repo
cd
to the root package directory- run following command
python -m unittest tests
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