def multiply(a, b): a * b

Question

Problem:

I recently started learning python programming. This is my very first attempt to write a code run the program. I tried to compile my program but it throwing me back an error.

def multiply(a, b):
  a * b

What should I do now?

Answer 1

As per your question, I understand that you want to make a function in your program that will multiply two different numbers. You need to keep in mind if you define a function it has to have a return value otherwise, it doesn’t make any sense.

So you have to have a return value in your function right this way:

def multiply(a, b):
  return a * b

Now, this should compile and run error-free. Thanks.

Answer 2

In case it is a function, it requires to return something. Else, running it is kind of useless.

So you possibly require to say:

def multiply(a, b):
  return a * b

You possibly want to read more about functions in Python and at the time this would make sense (passing by reference, for example). This can be a good starting point: Python functions.

There is no return value, the code will be OK

def multiply(a, b):
   return a * b

For example 111 x 101 gives:

 111
  x101
------
   111
  000
 111
 -----
 11011
 =====

We can illustrate 101 as x2+1x2+1 and 110 as x2+xx2+x

In next move we multiple them together to give:

(x2+1)×(x2+x)(x2+1)×(x2+x)

(x4+x3+x2+x)(x4+x3+x2+x)

which can be illustrated as 11110

For example in case we exercise the example on Page 6 [here] of 84 x 13 (and where ** represents "to the power of")

84x13 = ((2**6+ 2**4+ 2**2)x(2**3+ 2**2+ 2**0)) (mod 2)
      = (2**9+ 2**8+ 2**7+2**1+ 2**6+ 2**5+ 2**1 + 2**4+ 2**2) (mod 2)
      = (2**9+ 2**8+ 2**7+ 2**5+ 2**2) (mod 2)

which is 1110100100 [Calc]

The performing out in its proper form is:

84x13 = ((26+24+22)×(23+22+20))(mod2)
=(29+28+26+27+26+24+25+24+22)(mod2)
=(29+28+27+25+22)(mod2)

I have exercise a simple bit-shift operation and X-OR to implement the method:

import struct
import sys

val1=1
val2=1


if (len(sys.argv)>1):
        val1=str(sys.argv[1])

if (len(sys.argv)>2):
        val2=str(sys.argv[2])

def reverse(text):

    lst = []
    count = 1

    for i in range(0,len(text)):

        lst.append(text[len(text)-count])
        count += 1

    lst = ''.join(lst)
    return lst


def showpoly(a):
	str1 = ""
	nobits = len(a)


    	for x in range (0,nobits-2):
		if (a[x] == '1'):
			if (len(str1)==0):
				str1 +="x**"+str(nobits-x-1)	
			else: 
				str1 +="+x**"+str(nobits-x-1)

	if (a[nobits-2] == '1'):
		if (len(str1)==0):
			str1 +="x"
		else:
			str1 +="+x"

	if (a[nobits-1] == '1'):
		str1 +="+1"

	print str1;
	
def multiply(a,b):
	bit1 = int(a,2)
	bit2 = int(b,2)
	g = []
	nobits = len(b)	

	print a.rjust(len(a)+len(b)-1)
	str = "x"+b;
	print str.rjust(len(a)+len(b)-1)

	print "-" * (len(a)+len(b)-1)

	b=reverse(b)
	for i in range (0,nobits):
		if (b[i]=='0'):
			g.append(0)
		else:
			g.append(int((bit1<<i)))
		print bin(g[i])[2:].rjust(len(a)+len(b)-1)
	res=int(g[0])
	for i in range (1,nobits):
		res = int(res) ^ int(g[i])
	print "-" * (len(a)+len(b)-1)
	print bin(res)[2:].zfill(len(a)+len(b)-1)
	print "=" * (len(a)+len(b)-1)


	return res  


print "Binary form:\t",val1,"x",val2
print "Decimal form:\t",int(val1,2),"x",int(val2,2)
print ""
showpoly(val1)

showpoly(val2)

print "\nWorking out:\n"
res=multiply(val1,val2)

print "\nResult: ",res