How to make if statement true every four loops in Python

I am not sure on how to ask this question, i have searched but no results. Please help.

How can I make an if statement which will repeat itself every four times insede a for loop:

for x in range(0,20):
     print x
     if x >= 3:
         print ","

As you can see here I want the comma to reap evry four numbers and instead i get this:

0
1
2
3
,
4
,
5
,
6
,
7
,
8
,
9
,
10
,
11
.
. 
.

Since the numbers ahead of 3 are greater than 3. I am on python. Please help me.