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HHMathewChan

Posted on • Originally published at rebirthwithcode.tech

# Python Exercise 15 : Perform calculation on a string

## Question

• Create a function to perform basic arithmetic operations

• that includes additionsubtractionmultiplication 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
``````

### 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
``````

## 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
``````
• code
``````import operator

def arithmetic_operation(math_sting: str):
# split the string
splited_list = math_sting.split()
first_num = int(splited_list)
second_num = int(splited_list[-1])
operation_to_call = splited_list
# 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
``````

## 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
``````

## 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)
``````

## 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

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