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TypeScript arrays and Python lists handle many of the same everyday collection tasks, but they are not identical. TypeScript describes the element types of JavaScript arrays with annotations such as number[]; Python’s built-in list can hold objects of different types, even when a type annotation documents an intended element type.
How TypeScript arrays and Python lists differ
TypeScript uses JavaScript arrays at runtime and adds static type descriptions that help catch mistakes while code is checked. For example, number[] and Array<number> both describe an array whose elements are intended to be numbers. These annotations do not create different runtime containers.
const scores: number[] = [10, 20, 30];
const alsoScores: Array<number> = [10, 20, 30];Python’s built-in list is a mutable sequence that can contain arbitrary Python objects. An annotation can express the intended element type, but the built-in list itself is not restricted to that type.
Map common operations by intent
These pairs solve similar tasks, but they are language-specific operations rather than exact equivalents.
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| Task | TypeScript / JavaScript array | Python list |
|---|---|---|
| Add an item at the end | items.push(value) |
items.append(value) |
| Get the number of items | items.length |
len(items) |
| Check whether a value is present | items.includes(value) |
value in items |
| Take a portion of a sequence | items.slice(start, end) |
items[start:end] |
For example, the membership check changes order: TypeScript calls a method on the array, while Python places the value before in. Slicing is also expressed differently: the TypeScript call uses parentheses and the Python form uses brackets with a colon.
Account for Python methods that mutate a list
Python’s append, reverse, and sort methods modify the existing list. The methods return None, rather than returning the changed list for chaining.
values = [3, 1, 2]
values.append(4)
values.sort()
# values is now [1, 2, 3, 4]When translating code, keep the mutation separate from the value being changed. Do not assign the result of a mutating Python list method back to the list.
Use tuples when positions matter
A TypeScript tuple describes a positional shape: [string, number] means the first position is a string and the second is a number. This is useful for a fixed pair with different roles, rather than a collection where each item has the same type.
Python also has tuples, but they are not simply another spelling for a list. Lists are mutable; tuples are immutable and commonly represent fixed collections of values. As a guide, use a Python list for a sequence you intend to change, and a tuple for a fixed group. In TypeScript, use an array type for a collection and a tuple type when positions have specific meanings.
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A practical translation checklist
- Choose a TypeScript element type such as
number[]when the collection is intended to contain numbers; Python’s built-in list does not enforce a single element type by itself. - Translate the operation’s purpose, not just its spelling: use
appendfor adding to a Python list,lenfor its size, andvalue in itemsfor membership. - Check whether an operation mutates the original list, especially when using Python’s
append,reverse, orsort. - Use positional tuple types or values when the meaning depends on what each slot contains, rather than treating every sequence as interchangeable.
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