Python List vs. Array - when to use?


Question

If you are creating a 1d array, you can implement it as a List, or else use the 'array' module in the standard library. I have always used Lists for 1d arrays.

What is the reason or circumstance where I would want to use the array module instead?

Is it for performance and memory optimization, or am I missing something obvious?

1
340
7/13/2015 2:56:12 PM

Accepted Answer

Basically, Python lists are very flexible and can hold completely heterogeneous, arbitrary data, and they can be appended to very efficiently, in amortized constant time. If you need to shrink and grow your list time-efficiently and without hassle, they are the way to go. But they use a lot more space than C arrays.

The array.array type, on the other hand, is just a thin wrapper on C arrays. It can hold only homogeneous data, all of the same type, and so it uses only sizeof(one object) * length bytes of memory. Mostly, you should use it when you need to expose a C array to an extension or a system call (for example, ioctl or fctnl).

array.array is also a reasonable way to represent a mutable string in Python 2.x (array('B', bytes)). However, Python 2.6+ and 3.x offers a mutable byte string as bytearray.

However, if you want to do math on a homogeneous array of numeric data, then you're much better off using NumPy, which can automatically vectorize operations on complex multi-dimensional arrays.

To make a long story short: array.array is useful when you need a homogeneous C array of data for reasons other than doing math.

397
12/30/2018 9:51:20 AM

For almost all cases the normal list is the right choice. The arrays module is more like a thin wrapper over C arrays, which give you kind of strongly typed containers (see docs), with access to more C-like types such as signed/unsigned short or double, which are not part of the built-in types. I'd say use the arrays module only if you really need it, in all other cases stick with lists.


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