Using system.date.now() as default parameter

Ignition
,
1

It seems to me like using system.date.now() as a default parameter in a function is bad practice because...

This is easy to see within the script console, but when you apply this concept to the script library, you could call a function much later than a few seconds and it will use the an earlier value. Saving your project will cause this variable to be re-evaluated. See this example in the script console.

from time import sleep

def test(date=system.date.now()):
	return date

for i in range(10):
	sleep(1)
	test()
2

This is not a bug, it's working as intended.

Python named parameter values are evaluated once, when the function is defined, not every time the function is called.

2 Likes
3

Is the garbage collector the only condition that causes this value to need to be reevaluated?

4

No, GC is not relevant.

As far as Ignition goes, saving your project will cause it be re-evaluated because that's when all the script modules get loaded/executed and the function is defined.

1 Like
5

Try this if you really want a named parameter with a default value that is "live" each time:

def test(date=None):
	if not date:
		date = system.date.now()
5 Likes