How can I prevent the TypeError list indices must be integers not tuple when copying a python list to a numpy array

Question

I want to create 3 numpy arrays/lists using data from another array called mean_data as follows:

--  39 R = np.array(mean_data[:,0])
     40 P = np.array(mean_data[:,1])
     41 Z = np.array(mean_data[:,2])

I get this error when I run this code:

TypeError: list indices must be integers, not tuple

 I have tried creating mean_data as an np.array and using np.append to add values to it but that doesn't solve the problem either.

Here's the traceback:

Traceback (most recent call last):
  File "polarplot.py", line 36, in <module>
    R = np.array(mean_data[:,0])
TypeError: list indices must be integers, not tuple

This is how I tried creating an array:

mean_data = np.array([])

for ur, ua in it.product(uradius, uangle):
    samepoints = (data[:,0]==ur) & (data[:,1]==ua)
    if samepoints.sum() > 1:  # check if there is more than one match
        np.append(mean_data[ur, ua, np.mean(data[samepoints,-1])])
    elif samepoints.sum() == 1:
        np.append(mean_data, [ur, ua, data[samepoints,-1]])

This is the the traceback on that :

IndexError                                Traceback (most recent call last)
<ipython-input-3-5268bc25e75e> in <module>()
     31     samepoints = (data[:,0]==ur) & (data[:,1]==ua)
     32     if samepoints.sum() > 1:  # check if there is more than one match
---> 33         np.append(mean_data[ur, ua, np.mean(data[samepoints,-1])])
     34     elif samepoints.sum() == 1:
     35         np.append(mean_data, [ur, ua, data[samepoints,-1]])

IndexError: invalid index

Can someone guide me in solving this?