What happens if we don't declare variables before using them in Python?

[SubhanUllah]

>>> existing_variable=8 
>>> print(f"{existing_variable=}") 
existing_variable=8 
>>> print(f"{non_existing_variable=}") 
Traceback (most recent call last): 
  File "<pyshell#7>", line 1, in <module> 
    print(f"{non_existing_variable=}") 
NameError: name 'non_existing_variable' is not defined 
>>>