Write a function, `persistence`, that takes in a positive parameter `num` and returns its multiplicative persistence, which is the number of times you must multiply the digits in `num` until you reach a single digit.
For example:
```python
 persistence(39) => 3  # Because 3*9 = 27, 2*7 = 14, 1*4=4
                       # and 4 has only one digit.
 persistence(999) => 4 # Because 9*9*9 = 729, 7*2*9 = 126,
                       # 1*2*6 = 12, and finally 1*2 = 2.
 persistence(4) => 0   # Because 4 is already a one-digit number.
```
```python
 persistence(39) # returns 3, because 3*9=27, 2*7=14, 1*4=4
                 # and 4 has only one digit
 persistence(999) # returns 4, because 9*9*9=729, 7*2*9=126,
                  # 1*2*6=12, and finally 1*2=2
 persistence(4) # returns 0, because 4 is already a one-digit number
```
def persistence(n):
    n = str(n)
    count = 0
    while len(n) > 1:
        p = 1
        for i in n:
            p *= int(i)
        n = str(p)
        count += 1
    return count
    # your code

def persistence(n):
    n = str(n)
    count = 0
    while len(n) > 1:
        p = 1
        for i in n:
            p *= int(i)
        n = str(p)
        count += 1
    return count
    # your code
