(simple) problem with changing type and key error in Pandas

Question

DataFrame

x	y	num
0	0	7
1	0	8
1	1	9
1	2	10

def my_function(x,y):
    print(df["num"][(df["x"] == x) & (df["y"] == y + 1)])

x = my_function(1,1)
print(x)
print(type(x))

Out:
3    10
Name: num, dtype: int64
None
<class 'NoneType'>

I don't know why its becoming NoneType instead of pandas.series and how can i get "num" value here ("10")

x[0] gives key error :<