import pandas as pd
df = pd.read_csv("filename1.csv")

df
    column1  column2   column3
0        10       A          1
1        15       A          1
2        19       B          1
3      5071       B          0
4      5891       B          0
5      3210       B          0
6        12       B          2
7        13       C          2
8        20       C          0
9         5       C          3
10        9       C          3

df.column3.value_counts()

1   3
2   2
3   2

df
    column1  column2   column3
0        10       A          1
1        15       A          1
2        19       B          1