Variables in Python can be defined locally or globally. There are two types of variables first one is a local variable that is defined inside the function and the second one are global variable that is defined outside the function.
Method 1: Checking the existence of a local variable
To check the existence of variables locally we are going to use the locals() function to get the dictionary of the current local symbol table.
Python3
def func(): # defining local variable a_variable = 0 # for checking existence in locals() function if 'a_variable' in locals(): return True# driver codefunc() |
Output:
True
Method 2: Checking the existence of a global variable
To check the existence of variables globally we are going to use the globals() function to get the dictionary of the current global symbol table.
Python3
# defining local variablea_variable = 0def func(): # for checking existence in globals() function if 'a_variable' in globals(): return True# driver codefunc() |
Output:
False
Method 3: Testing if a Variable Is Defined or not using try and except
A NameError exception is raised when attempting to access a variable that hasn’t yet been defined, you can manage this with a try/except statement
Python3
# a_variable = 0try: a_variable print("Yes")except NameError: print("Error: No value detected") |
Output:
Error: No value detected
Using the ‘in’ keyword:
Approach:
You can use the ‘in’ keyword to check if a variable is defined or not.
Python3
if 'my_variable' in locals(): print('Variable exists')else: print('Variable does not exist') |
Variable does not exist
Time complexity: O(1)
Space complexity: O(1)
