numpy.ndarray
allHoldingsFund = pd.DataFrame({'ratioBest':[np.array(4.12), '']})
print (allHoldingsFund)
ratioBest
0 4.12
1
list
1d array
arr = np.array(allHoldingsFund['ratioBest'].tolist())
allHoldingsFund['ratioBest'] = (pd.to_numeric(arr, errors='coerce'))
print (allHoldingsFund)
ratioBest
0 4.12
1 NaN
print (allHoldingsFund['ratioBest'].dtype)
float64