Solve simple derivative questions

Question

Built my first script and its function is to solve simple derivative questions. How can I improve this code? This is my first time posting.

#This is Simple Derivative Solver
 def derivative():
     print("This program will give you the first derivative.")
     input("Press ENTER to continue...")
     cf=int(input("Enter the coefficient of the term..."))
     exp=int(input("Enter the exponent of the term..."))
     if exp==1 and cf==1:
        print("The answer is", 1)
     elif exp<0 and cf<0:
        print("The answer is:", abs(exp*cf), "x^", (exp-1))
     elif exp>0:
        print("The answer is:", exp*cf, "x^", (exp-1))
     elif exp==0:
        print("The answer is:", 0)
     elif exp<0:
        print("The answer is:", abs(exp*cf), "x^", (exp-1))
     elif cf==0:
        print("The answer is:", 0)
     elif cf<0:
        print("THe answer is:", cf*exp, "x^", (exp-1))
derivative()

Answer 1

• Trust the math. If exp<0 and cf<0, their product will be positive, so abs is redundant. BTW, in case of elif exp < 0, call to abs leads to an incorrect answer.

• In any case, \$(ax^n)'\$ always equals to \$anx^{n-1}\$. Mathematically speaking there are no special cases. There are special cases when it comes to printing:

  • \$n = 0\$: you (correctly) print 0

  • \$n = 1\$: you print x^0, but it is better to omit it altogether

  • \$n = 2\$: you print x^1, but it is better to print just x.

  • \$n < 0\$: consider printing parenthesis around the exponent.

• Separate concerns. The derivative shall only compute the derivative. Input shall be handled separately.

• The call to derivative should be conditionalized:

  if __name__ == `__main__`:
      derivative()
  

  This enables you to import your code in another project.

Answer 2

One other thing that is generally a good thing to do is to separate such function into pure function and side-effecting one that uses it. This will simplify testing, readability, memoization etc. Consider this alternative:

def derivative(coefficient, exponent):
    if exp == 1 and cf == 1:
        return 1,
    elif exp < 0 and cf < 0:
        return abs(exp * cf), 'x^', exp - 1
    elif exp > 0:
        return exp * cf, 'x^', (exp-1)
    elif exp == 0:
        return 0
    elif exp < 0:
        return abs(exp * cf), 'x^', exp - 1
    elif cf == 0:
        return 0
    elif cf < 0:
        return cf * exp, 'x^', exp - 1


if __name__ == '__main__':
    print('This program will give you the first derivative.')
    input('Press ENTER to continue...')
    cf = int(input('Enter the coefficient of the term...'))
    exp = int(input('Enter the exponent of the term...'))
    derivative(cf, exp)