What are the key differences between using list() and []?

The most obvious and visible key difference between [python]list()[/python] and [python][][/python] is the syntax. Putting the syntax aside for a minute here, someone whose new or intermediately exposed to python might argue that they’re both lists or derive from the same class; that is true. Which furthermore increases the importance of understanding the key differences of both, most of which are outlined below.

[python]list()[/python] is a function and [python][][/python] is literal syntax.

Let’s take a look at what happens when we call [python]list()[/python] and [python][][/python] respectively through the disassembler.

[python]>>> import dis >>> print(dis.dis(lambda: list())) 1 0 LOAD_GLOBAL 0 (list) 3 CALL_FUNCTION 0 (0 positional, 0 keyword pair) 6 RETURN_VALUE None >>> print(dis.dis(lambda: [])) 1 0 BUILD_LIST 0 3 RETURN_VALUE None[/python] The output from the disassembler above shows that the literal syntax version doesn’t require a global lookup, denoted by the op code LOAD_GLOBAL or a function call, denoted by the op code CALL_FUNCTION.

As a result, literal syntax is faster than it’s counterpart. – Let’s take a second and look at the timings below.

[python]import timeit >>> timeit.timeit(‘[]’, number=10**4) 0.0014592369552701712 >>> timeit.timeit(‘list()’, number=10**4) 0.0033833282068371773[/python] On another note it’s equally important and worth pointing out that literal syntax, [python][][/python] does not unpack values. An example of unpacking is shown below.

[python] >>> list(‘abc’) # unpacks value [‘a’, ‘b’, ‘c’] >>> [‘abc’] # value remains packed [‘abc’] [/python]

What’s a literal in python? ¶

Literals are notations or a way of writing constant or raw variable values which python recognises as built-in types.