DEV Community

HHMathewChan
HHMathewChan

Posted on • Originally published at rebirthwithcode.tech

Python Exercise 15 : Perform calculation on a string

#beginners #python #challenge

Question

  • Create a function to perform basic arithmetic operations

    • that includes addition, subtraction, multiplication and division 
    • on a string number

  • For the challenge, we are going to have only two numbers and 1 valid operator in between.

  • The return value should be a number.

Restriction

  • eval() is not allowed.

  • In case of division, whenever the second number equals "0" return -1.

"15 // 0" ➞ -1
Enter fullscreen mode Exit fullscreen mode

Example 

arithmetic_operation("12 + 12") ➞ 24 // 12 + 12 = 24 arithmetic_operation("12 - 12") ➞ 24 // 12 - 12 = 0 arithmetic_operation("12 * 12") ➞ 144 // 12 * 12 = 144 arithmetic_operation("12 // 0") ➞ -1 // 12 / 0 = -1
Enter fullscreen mode Exit fullscreen mode

My attempt

  • algorithm 
>>separate the number and operator in the string by space call split() method >>perfrom action based whether it is a number or valid operator import operator module build a dictionary with key=the operator string, value = the equivent function check the second separated part, which must be operator, to call the equivent function from the dictionary pass the first and thrid element as argument to the function >>return the result
Enter fullscreen mode Exit fullscreen mode
  • code 
import operator def arithmetic_operation(math_sting: str): # split the string  splited_list = math_sting.split() first_num = int(splited_list[0]) second_num = int(splited_list[-1]) operation_to_call = splited_list[1] # In case of division, whenever the second number equals "0" return`-1`.  if operation_to_call == "//" and second_num == 0: return -1 # setup dictionary to call the maths operation  math_dictionary = {"+": operator.add(first_num, second_num), "-": operator.sub(first_num, second_num), "*": operator.mul(first_num, second_num), "//": operator.floordiv(first_num, second_num)} # find the equivalent operation from the dictionary and store the result  result = math_dictionary[operation_to_call] return result
Enter fullscreen mode Exit fullscreen mode

Other solution 

def arithmetic_operation(equation): ''' Returns the result of evaluating the string equation ''' from operator import add, sub, floordiv, mul operator_dict = {'+': add, '-': sub, '*': mul, '//': floordiv} # split the equation into three part  first_num, operation, second_num = equation.split() try: # call the operation from the dictionary and perform the calculation  return operator_dict[operation](int(first_num), int(second_num)) # In case of division, whenever the second number equals "0" return`-1`.  except ZeroDivisionError: return -1
Enter fullscreen mode Exit fullscreen mode

Easiest understand method 

def arithmetic_operation(equation): first_num, operation, second_num = equation.split() if operation == '+': return int(first_num) + int(second_num) if operation == '-': return int(first_num) - int(second_num) if operation == '*': return int(first_num) * int(second_num) if operation == '//' and second_num == '0': return -1 return int(first_num) // int(second_num)
Enter fullscreen mode Exit fullscreen mode

My reflection

  • I have learned that import statement can be exist inside a function. When you expect an error would occur, should use exceptional handling to deal with it.

Credit

challenge on edabit

Top comments (0)