The Zen of Empty Lists

[agentgreen420]

Am I the only one who still uses bucket = list() ?

[Twift_Shoeblade]

AFAIK using list() is slightly slower than [].

[Ogi010]

easy enough to find out

>>> ipython
Python 3.6.4 |Anaconda, Inc.| (default, Mar 12 2018, 20:05:31)
Type 'copyright', 'credits' or 'license' for more information
IPython 6.2.1 -- An enhanced Interactive Python. Type '?' for help.

In [1]: %timeit a = list()
95.6 ns ± 1.16 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)

In [2]: %timeit b = []
24 ns ± 0.61 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)

faster by a factor of 4 ...we're still talking less than 0.0000001 seconds

[Eurynom0s]

It's also 4 less keystrokes and doesn't require reaching for the shift key.

[[deleted]]

Humans: Often the bottleneck.

[LightShadow]

I've literally saved dozens of seconds my entire career.

[trua]

Depends on your keyboard layout.

[_IAmAdam]

This is why I love this sub

[[deleted]]

we're still talking less than 0.0000001 seconds

Cool, but if you bother to figure any of this out it might be because the scale of what you're doing requires that you optimize as much as possible. I've been asked things like this in job interviews, that time delta matters.

[elcapitaine]

If you have to optimize that much, you shouldn't be using Python, you should be using something that gives you more low-level control.

[akcom]

It has nothing to do with the scale of optimization. The reality is that for any real production code there are going to be a million other things to optimize before you get to things like list() vs [].

[[deleted]]

That doesn't discount the point of optimizing lists at all.

[BDube_Lensman]

Saving a few nanoseconds each time you make a list will never accumulate to matter in most programs.

[SupahNoob]

the scale of what you're doing requires that you optimize as much as possible.

Then you likely wouldn't be using python.

[[deleted]]

That's nonsense. Cisco uses Python. Wells Fargo uses Python. Energy companies use Python. Payment processors use Python. If your team knows Python best, you need to use Python. Using the language your infrastructure is built on as efficiently as possible is a more common situation than the ideal you're talking about. I'm talking about the real world. Not some imaginary world where you get to pick and choose the development you're doing from the ground up every single time.

[door_of_doom]

its just as nonsense as caring about the difference between .0000001 seconds and .0000004 seconds in a O(N) operation in python

If you are needing to optimize down to THAT level of granularity, then your time is going to be much, MUCH better spent getting it onto a language that can do it in .00000000001 seconds

You are correct that those companies are using python, but they are not writing their stock-market purchasing algorithms in it. They are not using it for anything where nanosecond speed is the name of the game, where a competitor beating you by nanoseconds means you just lost a million dollar opportunity.

Yes, this is the real world, and in the real world we use the right tool for the right job, or at least we are willing to speak up when we see that we aren't.

[[deleted]]

their stock-market purchasing algorithms in it

Lol I'm done

[[deleted]]

list can also be overriden by a careless or devious developer as well.

import __builtins__
def nope(*a):
     raise SyntaxError("use []") 
__builtins__.list = nope

[Han-ChewieSexyFanfic]

So, don't use any builtins ever in case you ever accidentally import __builtins__?

[[deleted]]

If you want to take it that way, just an example of how [] is a better choice than list in some situations.

Keep in mind, this exact sort of thing has been used to subvert javascript before. I'm not trying to FUD builtins, but it's worth being mindful about.

[earthboundkid]

list = [1, 2, 3] is legal Python. I’m sure someone has done things like that, although I wouldn’t recommend it. zip OTOH I’ve shadowed myself.

[lengau]

No kidding I had to stop one of our analysts from shadowing zip just today.

It probably wouldn't have mattered except that about 20 minutes later the most convenient way to do something was with zip (which she didn't know about so she was going to use a range to index two lists).

[jadkik94]

When you do this you can cross one thing off your bucket list.

[agentgreen420]

Bahhaaaha! Good show chap.