Function to check if dictionary value is occupied
Solution 1:
The issue is in the way you referenced the value of the 'key'. Use this:
XO = {'key': []}
def check_values(input_v):
value = input_v
global XO
#print(XO)
if value in XO['key']:
print("Occupied")
else:
XO['key'].append(value)
#print(XO)