An array is an ordered collection of elements, and the elements can be of mixed data types. Arrays themselves are considered to be a composite data type. Python uses lists as an equivalent type. One key difference between lists and arrays is how memory is allocated. Elements of an array must be saved in adjacent or contiguous memory locations. This constraint allows for quick access of an element, but slow insertion or modification. Elements of a list, in contrast, can be saved anywhere and each element is saved with a reference to the previous element’s location. This arrangement results in fast insertion or updating of a list, but relatively poor access speed.
Arrays are often created by using square brackets
 with a comma-separated list of individual elements inside:
array = [element0, element1, element2, element3]
Nested arrays (arrays within arrays) are also possible:
nested = [elementB, elementC] outer = [elementA, nested, element4]
The length of the
outer array is 3 elements-long because the inner
nested array counts as an individual element. By itself, the
nested array is 2 elements-long.
Array elements are usually referenced by an index number, which represents their position in the sequence.
The indices of most arrays start with 0:
groceryList = ["milk", "cookies", "berries", "carrots"] // index: 0 1 2 3
- The first element
"milk"is at index 0.
- The second element
"cookies"is at index 1.
- …and so on.
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