Lesson Learned #269: Unable to connect - Is unavailable or does not exist - Connection Time out

Getting Same error while trying to connect Sql Server Database MS Community Could you please take a look I have shared  code snap and exception:
My Code:

import pymssql

def readdata_pymssql():
print('conn details of pymssql')
connectionString = f'SERVER={SERVER};DATABASE={DATABASE};UID={USERNAME};PWD={PASSWORD}'
#conn = pymssql.connect(connectionString,as_dict=True)
print(pymssql)
conn = pymssql.connect(server='.\SQLEXPRESS',user='sa',password=PASSWORD,database=DATABASE, as_dict=True)
print('Connected..')
SQL_QUERY = """
SELECT
* from books;
"""
cursor = conn.cursor()
cursor.execute(SQL_QUERY)

records = cursor.fetchall()
print(records)

DB_Conn.readdata_pymssql()

Exception:

Traceback (most recent call last):
File "C:\RND\pythonRND\DB_Conn.py", line 44, in <module>
DB_Conn.readdata_pymssql()
File "C:\RND\pythonRND\DB_Conn.py", line 30, in readdata_pymssql
conn = pymssql.connect(server='.\SQLEXPRESS',user='sa',password=PASSWORD,database=DATABASE, as_dict=True)
File "src\\pymssql\\_pymssql.pyx", line 653, in pymssql._pymssql.connect
pymssql._pymssql.OperationalError: (20009, b'DB-Lib error message 20009, severity 9:\nUnable to connect: Adaptive Server is unavailable or does not exist (localhost)\nDB-Lib error message 20009, severity 9:\nUnable to connect: Adaptive Server is unavailable or does not exist (localhost)\n')