def test1():
num = int(input('please enter a number'))
if num % 2 == 0: #Determine whether the input number is even
reture True #If it is even, the program exits and returns true
print('If it is not even, please re-enter')
return test1() #If it is not even, continue to call yourself and enter the value
print(test1()) #call test1
Recursion: a function calls itself
Disadvantages:
1. The recursion is the most recursive 999 times.
2. The efficiency of recursion is not high