Binary to Decimal Conversion

'''How to read a number from the user and convert to decimal'''

'''Ask user to enter an 8 digit binary number'''
import sys
binary = input ("please enter an 8 digit binary number: ")

'''Checking for binary length'''
if len(binary)>8 or len(binary)<8:
	print ('Please enter an 8-bit binary number')
	sys.exit

# checking for valid binary digits
d = 0
count = 0
for d in binary:
	if d =='0' or d == '1':
		continue
else:
	print('Binary number must contain combinations of 1s and 0s.' )
sys.exit()


# converting binary to decimal
d = 0
count = 0

for b in binary:
	d = d + int (b) * (2 ** count)
count = count + 1

# displaying the equivalent decimal number
print('The decimal equivalent of the binary number is: ' (d))