Python program to compute arithmetic operation from String

Arithmetic operations are mathematical calculations performed on numeric data types. Python supports several arithmetic operators that can be computed from string expressions.

• Addition (+)

• Subtraction ()

• Multiplication (*)

• Division (/)

• Floor Division (//)

• Modulo (%)

• Exponentiation (**)

There are several ways to compute arithmetic operations from strings. Let's explore different approaches with their advantages and limitations.

Using the eval() Function

The eval() function evaluates a string expression and returns the result. This is the simplest approach but should be used cautiously due to security risks.

Example

The eval() function directly evaluates the mathematical expression and follows proper operator precedence ?

def compute_operation(expression):
    result = eval(expression)
    return result

expression = "2 + 3 * 4 - 6 / 2"
result = compute_operation(expression)
print("The result of the given expression:", result)

The output of the above code is ?

The result of the given expression: 11.0

Using Custom Parsing (Left-to-Right Evaluation)

For more control and safety, we can implement custom parsing. This approach evaluates expressions from left to right without considering operator precedence.

Example

This method splits the expression and processes operators sequentially ?

def compute_operation(expression):
    operators = {'+': lambda x, y: x + y,
                 '-': lambda x, y: x - y,
                 '*': lambda x, y: x * y,
                 '/': lambda x, y: x / y}
    
    tokens = expression.split()
    result = float(tokens[0])
    
    for i in range(1, len(tokens), 2):
        operator = tokens[i]
        operand = float(tokens[i+1])
        result = operators[operator](result, operand)
    
    return result

expression = "2 + 3 * 4 - 6 / 2"
result = compute_operation(expression)
print("The result of given expression:", result)

The output of the above code is ?

The result of given expression: 7.0

Using the operator Module

The operator module provides functions corresponding to built-in Python operators, offering a cleaner and more readable approach.

Example

This approach maps string operators to their corresponding functions from the operator module ?

import operator

def compute_operation(expression):
    ops = {
        '+': operator.add,
        '-': operator.sub,
        '*': operator.mul,
        '/': operator.truediv,
    }
    
    tokens = expression.split()
    result = float(tokens[0])
    
    for i in range(1, len(tokens), 2):
        operator_func = ops[tokens[i]]
        operand = float(tokens[i + 1])
        result = operator_func(result, operand)
    
    return result

expression = "10 + 5 * 2"
result = compute_operation(expression)
print("The arithmetic operation result:", result)

The output of the above code is ?

The arithmetic operation result: 30.0

Comparison

Conclusion

Use eval() only with trusted input due to security risks. For safer alternatives, implement custom parsing or use the operator module. Choose based on whether you need operator precedence or prefer left-to-right evaluation.