How do I make an assignment inside lambda function?

[Standard_user]

Good day,
having a brain freeze :) How do I set a boolean variable to True inside lambda function? I'm trying to set variable to True on a hotkey(using SystemHotkey lib) :

from system_hotkey import SystemHotkey

b = False
SystemHotkey().register(('control', 'e'), callback = lambda : b = True)

But this spits out a syntax error.  Also tried:

SystemHotkey().register(('control', 'e'), callback = lambda : exec('b = True'))

But it just doesn't work. Any ideas, please?