Example - find first occurence of a number in a list:
from random import randint
l1 = [randint(1, 100) for num in range(1000)]
i = 0
num_to_search = 65
while i < len(l1):
if l1[i] == num_to_search:
print(f"{num_to_search} found at index {i}")
break
i += 1
Output:
65 found at index 147