Passing arguments with lambda functions

[laserir]

Hi all,

I create buttons dynamically after loading a json file like so:

i = 0
for users in settings["users"]:
     user_buttons[i] = ui.button(users['name'], on_click=lambda: set_userto(users['id']))
     i = i+1

Problem is ALL buttons call set_userto(4)

Any ideas?

[rodja]

You need to capture the value of users at the time each button is created:

for i, user in enumerate(settings["users"]):
     user_buttons[i] = ui.button(user['name'], on_click=lambda e, user=user: set_userto(user['id']))

[falkoschindler]

Note that this is independent of NiceGUI. Lambda statements don't capture the current value of variables in a for loop:

callbacks = []
for letter in ['A', 'B', 'C']:
    callbacks.append(lambda: print(letter))

for callback in callbacks:
    callback() # output: C C C

Like @rodja says you need to capture the current letter:

callbacks = []
for letter in ['A', 'B', 'C']:
    callbacks.append(lambda letter=letter: print(letter))

for callback in callbacks:
    callback() # output: A B C

[laserir]

Thanks! Anyhow... now it throws me this exception when the on_click is triggered (creation of the buttons still works fine):
TypeError: 'ClickEventArguments' object is not subscriptable

[falkoschindler]

Oh, there's a little mistake in @rodja's code: lambda user=user: overwrites the optional event arguments a button click handler expects. Replace it with something like lambda e, user=user: and it should work.

It's sometimes difficult to help with incomplete code examples because we can't easily try them out.

Edit: I fixed Rodja's code.

[laserir]

Thank you guys so much!!! Really appreciate your work!