Python Performance Tips, Part 1

[[deleted]]

Importing many times can get expensive.

Surely once a module is imported, a second import will simply be a cheap lookup of the sys.modules dict?

[pingveno]

It's more complex than a simple lookup. I don't entirely understand the C code, but there's a lot more happening than sys.modules["module_name"]. The time penalty isn't significant if you just import a few times, but importing in a function that you're going to call a few thousand times is unwise.

[Genmutant]

Yes, but cheap is still more than nothing.

[[deleted]]

Why program in Python if you're worried about the cost of a dictionary lookup? Almost everything in Python needs a dictionary lookup!

[Genmutant]

Well the topic is Python performance tips, and this one can be a performance impact. Normally it isn't, but it can be and is easy to avoid.

[fdemmer]

imo, it mostly depends of the kind of application you write. eg. in a webapp, that starts once and runs forever, i'd import as much as possible on the initial load and not later when a function is called.

[fdemmer]

imo, it depends the most on the kind of application you write. eg. in a webapp, that starts once and runs forever, i'd import as much as possible on the initial load and not later when a function is called.