**To write a Python Program to perform binary search. **

def binary_search(alist, key):

“””Search key in alist[start… end – 1].”””

start = 0

end = len(alist)

while start < end:

mid = (start + end)//2

if alist[mid] > key:

end = mid

elif alist[mid] < key:

start = mid + 1

else:

return mid

return -1

alist = input(‘Enter the sorted list of numbers: ‘)

alist = alist.split()

alist = [int(x) for x in alist]

key = int(input(‘The number to search for: ‘))

index = binary_search(alist, key)

if index < 0:

print(‘{} was not found.’.format(key))

else:

print(‘{} was found at index {}.’.format(key, index))

**OUTPUT:**

Enter the sorted list of numbers: 1 2 3 4 5 6 7 8 9

The number to search for: 4

4 was found at index 3.