def add(n1, n2):
  return n1 + n2

def subtract(n1, n2):
  return n1 - n2

def multiply(n1, n2):
  return n1 * n2

def divide(n1, n2):
  return n1 / n2

operations = {
  "+": "add",
  "-": "subtract",
  "*": "multiply",
  "/": "divide"
}

num1 = int(input("What's the first number?: "))
num2 = int(input("What's the second number?: "))

for operation in operations:
  print(operation)

operation_symbol = input("Pick an operation from the line above: ")

calculation_function = operations[operation_symbol]
answer = calculation_function(num1, num2)

print(f"{num1} {operation_symbol} {num2} = {answer}")

它给出了以下错误：

Traceback (most recent call last):
  File "main.py", line 34, in <module>
    answer = calculation_function(num1, num2)
TypeError: 'str' object is not callable

我认为它给出了错误，因为我使用的字符串从字典，但不知道如何修复它。