1. What is a NumPy array?
2. What is the output of the following code snippet?

import numpy as np
# input array
in_arr1 = np.array([[ 1, 2, 3], [ -1, -2, -3]] )
print ("1st Input array : 
", in_arr1) 
in_arr2 = np.array([[ 4, 5, 6], [ -4, -5, -6]] )
print ("2nd Input array : 
", in_arr2) 
# Stacking the two arrays horizontally
out_arr = np.hstack((in_arr1, in_arr2))
print ("Output stacked array :
 ", out_arr)

3. How do you sum a small array faster than np.sum? 
4. How do you delete indices, rows, or columns from a Pandas DataFrame?
5. How do you write a Pandas DataFrame to a file?
6. What is NaN in pandas ?
7. How do you remove duplicates from a pandas DataFrame ?
8. How do you change the size of figures drawn with Matplotlib?
9. What are the alternatives available for plotting graphs using Python ?