How to delete last N rows from Numpy array?

# importing numpy module
import numpy as np
# create an array with 6 rows and 3 columns
a = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9], 
              [10, 11, 12], [13, 14, 15], [16, 17, 18]])
print(a)
# delete last 1 st row
print("data after deleting last one row ", a[:-1])
# delete last 2 nd  row
print("data after deleting last two  rows ", a[:-2])
# delete last 3 rd  row
print("data after deleting last theww  rows ", a[:-3])
# delete last 4 th  row
print("data after deleting last four  rows ", a[:-4])
# delete last 5 th  row
print("data after deleting last five  rows ", a[:-5])
# delete last 6 th  row
print("data after deleting last six  rows ", a[:-6])

# importing numpy module
import numpy as np
# create an array with 5 rows and 
# 4 columns
a = np.array([[21, 7, 8, 9], [34, 10, 11, 12], 
              [1, 3, 14, 15], [1, 6, 17, 18], 
              [4, 5, 6, 7]])
# use for loop to iterate over the
# elements
for i in range(1, len(a)+1):
    print("Iteration No", i, "deleted", i, "Rows")
    print("Remaining data present in the array is\n ", a[:-i])

# importing numpy module
import numpy as np
# create an array with 5 rows and 
# 4 columns
a = np.array([[21, 7, 8, 9], [34, 10, 11, 12], 
              [1, 3, 14, 15], [1, 6, 17, 18],
              [4, 5, 6, 7]])
# place first 2 rows in b variable 
# using slice operator
b = a[:2]
print(b)

# importing numpy module
import numpy as np
# create an array with 5 rows and 
# 4 columns
a = np.array([[21, 7, 8, 9], [34, 10, 11, 12], 
              [1, 3, 14, 15], [1, 6, 17, 18], 
              [4, 5, 6, 7]])
# delete last three rows
# using numpy.delete
a = np.delete(a, [2, 3, 4], 0)
print(a)

# importing numpy module
import numpy as np
# create an array with 5 rows and 4 columns
a = np.array([[21, 7, 8, 9], [34, 10, 11, 12], 
              [1, 3, 14, 15], [1, 6, 17, 18], 
              [4, 5, 6, 7]])
# delete last three rows
# using numpy.delete
a = np.delete(a, [0, 1, 2, 3, 4], 0)
print(a)