counting the number of non-zero numbers in a column of a df in pandas/python

Use double sum:

print df
   a  b  c  d  e
0  0  1  2  3  5
1  1  4  0  5  2
2  5  8  9  6  0
3  4  5  0  0  0

print (df != 0).sum(1)
0    4
1    4
2    4
3    2
dtype: int64

print (df != 0).sum(1).sum()
14

If you need count only column c or d:

print (df['c'] != 0).sum()
2

print (df['d'] != 0).sum()
3

EDIT: Solution with numpy.sum:

print ((df != 0).values.sum())
14