Count occurrences of items in Series in each row of a DataFrame

Question

I have a pandas.DataFrame that looks like this.

COL1    COL2    COL3
C1      None    None
C1      C2      None
C1      C1      None
C1      C2           


        

Answer 1

Andy's answer is spot on.

I'm adding this answer, if C1,C2...Cn list is huge and we want to view only subset of them.

dff = df.copy()
dff['C1']=(df == 'C1').T.sum()
dff['C2']=(df == 'C2').T.sum()
dff['C3']=(df == 'C3').T.sum()
dff
  COL1  COL2  COL3  C1  C2  C3
0   C1  None  None   1   0   0
1   C1    C2  None   1   1   0
2   C1    C1  None   2   0   0
3   C1    C2    C3   1   1   1