Counting non zero values in each column of a DataFrame in python

My favorite way of getting number of nonzeros in each column is

df.astype(bool).sum(axis=0)

For the number of non-zeros in each row use

df.astype(bool).sum(axis=1)

(Thanks to Skulas)

If you have nans in your df you should make these zero first, otherwise they will be counted as 1.

df.fillna(0).astype(bool).sum(axis=1)

(Thanks to SirC)