![]() Guaranteed to be of type int, the last element is guaranteed to be This enables us to specify types such as Tuple, str] - a tuple type where the first element is That is, *Tuple remains *Tuple there’s no Unpacking an unbounded tuple preserves the unbounded tuple as it is. Unpacking a concrete tuple type is analogous to unpacking a tuple of Since we can unpack a TypeVarTuple, for consistency, we alsoĪllow unpacking a tuple type. We mentioned that a TypeVarTuple stands for a tuple of types. z = prefix_tuple ( x = 0, y = ( True, 'a' )) # Inferred type of z is Tuple Unpacking Tuple Types T = TypeVar ( 'T' ) Ts = TypeVarTuple ( 'Ts' ) def prefix_tuple ( x : T, y : Tuple ) -> Tuple. Operator that can be used in place of the star operator: Variable tuples in older versions of Python, we introduce the Unpack type Note that the use of the star operator in this context requires a grammar change,Īnd is therefore available only in new versions of Python. Indicator that the type variable tuple is not a normal type variable. To improve readability: the star also functions as an explicit visual.In a packed or unpacked form (“Hmm, should I write ‘ -> Shape’, To avoid potential confusion about whether to use a type variable tuple.This is, in fact, deliberately not possible: type variable tuples mustĪlways be used unpacked (that is, prefixed by the star operator). Why is this necessary - if Shapeīehaves like Tuple, couldn’t we have annotated the shape Note that in the previous example, the shape argument to _init_ is Array Type Variable Tuples Must Always be Unpacked ![]() _shape shape = ( Height ( 480 ), Width ( 640 )) x : Array = Array ( shape ) y = abs ( x ) # Inferred type is Array z = x + x #. _shape : Tuple = shape def get_shape ( self ) -> Tuple : return self. Type such as int, a type variable tuple is a stand-in for a tuple type such asĬlass Array ( Generic ): def _init_ ( self, shape : Tuple ): self. In the same way that a normal type variable is a stand-in for a single Unpacking a TypeVarTuple or tuple type is the typingĮquivalent of unpacking a variable or a tuple of values. TypeVarTuple instances and tuple types such as Tuple. In addition, we introduce a new use for the star operator: to ‘unpack’ This serves as a placeholder not for a single type In order to support the above use cases, we introduce (Note also that for the rest of this PEP, for conciseness of example, we useĪ simpler version of Array which is generic only in the shape - not the Ways of using Array is preferable that decision is left to library authors. In this PEP, but this PEP is agnostic about which of these two (or possibly other) The shape of variables is often just as important as the variable type.įor example, consider the following function which converts a batch įrom typing import Literal as L x : Array, L ] = Array ()įor consistency, we use semantic axis annotations as the basis of the examples In the context of numerical computation with libraries such as NumPy and TensorFlow, Large impact, and the main case this PEP targets - concerns typing in One particular use case - a use case with potentially Variadic generics have long been a requested feature, for a myriad of This gives individual type checkers some leeway, but can be tightened Multiple unpackings in a type expression aren’t specified precisely. This PEP was accepted for Python 3.11, with the caveat that details around To catch shape-related bugs in code that uses these libraries. Parameterised with the array shape, enabling static type checkers In numerical computing libraries such as NumPy and TensorFlow to be In particular, it allows the type of array-like structures This enables a wide variety of use cases. With an arbitrary number of types - that is, a variadic type variable,Įnabling variadic generics. In this PEP, we introduce TypeVarTuple, enabling parameterisation PEP 484 introduced TypeVar, enabling creation of generics parameterised Alternatives (Why Not Just Use Unpack?).Unspecified Type Parameters: Tuple vs TypeVarTuple.Overloads for Accessing Individual Types.Aliases with Both TypeVars and TypeVarTuples.Variadic Arguments Require Variadic Aliases. ![]()
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