explained if name main python

1# Suppose this is foo.py.
2
3print("before import")
4import math
5
6print("before functionA")
7def functionA():
8    print("Function A")
9
10print("before functionB")
11def functionB():
12    print("Function B {}".format(math.sqrt(100)))
13
14print("before __name__ guard")
15if __name__ == '__main__':
16    functionA()
17    functionB()
18print("after __name__ guard")