Fixing some errors

calculator/expression.py

 """
 Expression module defines the structure of an expression.
 """
-from calculator.operators import Operator
 from typing import Union
+from calculator.operators import Operator
 
 Term: type = int
 Token: type = Union[Operator, Term]
@@ -12,6 +12,7 @@ class OperatorExpression:
     """
     OperatorExpression class is an expression that contains an operator and two sub-expressions.
     """
+
     def __init__(self, operator: Operator, left, right):
         self.operator = operator
         self.left = left
@@ -28,6 +29,7 @@ class TermExpression:
     """
     TermExpression class is an expression that contains a single term.
     """
+
     def __init__(self, value: Term):
         self.value = value
 

calculator/operators.py

 """
 Operator module contains the Operator class and a list of standard operators.
 """
+
+
 class Operator:
     """
     Operator class is a binary operator with a symbol, a precedence and an evaluation function.
     """
+
     def __init__(self, symbol, precedence, evaluate_function):
         self.symbol = symbol
         self.precedence = precedence
@@ -17,4 +20,8 @@ class Operator:
         return self.evaluate_function(left, right)
 
 
-STANDARD_OPERATORS = { '+': Operator('+', 1, lambda a, b: a + b),'-': Operator('-', 1, lambda a, b: a - b),'*': Operator('×', 2, lambda a, b: a * b),'/': Operator('/', 2, lambda a, b: a / b)}
+STANDARD_OPERATORS = {
+    '+': Operator('+', 1, lambda a, b: a + b),
+    '-': Operator('-', 1, lambda a, b: a - b),
+    '*': Operator('×', 2, lambda a, b: a * b),
+    '/': Operator('/', 2, lambda a, b: a / b)}

calculator/server.py

-from calculator.calculator import Calculator
 from fastapi import FastAPI
 from fastapi.requests import Request
 from fastapi.templating import Jinja2Templates
+from calculator.calculator import Calculator
 
 app = FastAPI()
 templates = Jinja2Templates(directory="calculator/templates")
 calc = Calculator()
 
+
 @app.get("/")
 async def root(request: Request):
     """