diff --git a/calculator/expression.py b/calculator/expression.py
index 1a27f0c5c27494a971e1479b48bd5c6da9f3ae59..ab3383c284b15e5b9e412e996157a9d053a18e34 100644
--- a/calculator/expression.py
+++ b/calculator/expression.py
@@ -1,8 +1,8 @@
 """
 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]
diff --git a/calculator/operators.py b/calculator/operators.py
index f855332c2cbd379592f4dba51d8c8c66e8c1593d..5b643ab13bdad39d1d359035b72b2ba0284c7377 100644
--- a/calculator/operators.py
+++ b/calculator/operators.py
@@ -6,9 +6,9 @@ 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
-      self.evaluate_function = evaluate_function
+        self.symbol = symbol
+        self.precedence = precedence
+        self.evaluate_function = evaluate_function
 
     def __repr__(self):
         return self.symbol
diff --git a/calculator/server.py b/calculator/server.py
index e0dc49ae37812a16bb365a45c95771af16f114b5..c8dfb15704edd9b50b6f783cc554e9a5f4f3181d 100644
--- a/calculator/server.py
+++ b/calculator/server.py
@@ -1,7 +1,10 @@
-from calculator.calculator import Calculator
+"""
+Run server
+"""
 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")