(Python) working out the mean of a column in a 2d array

  arrays, multidimensional-array, python-3.x

i cant figure out how to calculate the mean for the values of the individual columns, for the rows its easy enough. the code should work for any amount of columns and rows no matter if data is removed or added to the array. it should also work if the ranges of the rows are different.

thank you in advance.

Source: Python-3x Questions