What can I improve about this code in order to be production-ready? I’m not worried about security but about errors that could occur.

What exceptions should I catch? I feel overwhelmed about exceptions because I feel that there are a lot of exceptions that one can consider.

What else should I do? Should I do unit testing for this?

The script first loads the client list from an SQL database, then takes the daily work quantity about pallet movements from a SQL database, after that it writes a .csv file with this data, and finally sends it through email.

import pyodbc
import csv
import smtplib
import os.path
from datetime import date, timedelta
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
from email.mime.application import MIMEApplication


def load_clients():
    client_list = {}
    connection_string = f'*'
    query = """
          SELECT clifor.a1_codice_clifor, anacf.ragione_soc_fiscale
            FROM anacf anacf, clifor clifor
           WHERE (clifor.a1_ditta_codice=5)
             AND (clifor.a1_tipo_cli1_for2=1)
             AND
              (anacf.a1_codice_anagrafica_generale=clifor.a2_anagrafica_codice)
    """
    cnxn = pyodbc.connect(connection_string, autocommit=True)
    with cnxn:
        cursor = cnxn.cursor()
        cursor.execute(query)
        while True:
            row = cursor.fetchone()
            if not row:
                break
            client_list[row[0]] = row[1]
    return client_list


def load_movements(clients):
    movement_list = []
    connection_string = f'*'
    query = """
          SELECT datadoc, cliente,
            SUM (@DECODE(tipodoc, 3 ,palletts)) AS inputs,
            SUM (@DECODE(tipodoc, 5 ,palletts)) AS outputs
              FROM docmagat
           WHERE ditta=5
             AND anno=2020
             AND tipodoc in (3,5)
             AND datadoc=SYSDATE-1
           GROUP BY 1,2
    """
    cnxn = pyodbc.connect(connection_string)
    with cnxn:
        cursor = cnxn.cursor()
        cursor.execute(query)
        while True:
            row = cursor.fetchone()
            if not row:
                break
            inputs = 0 if row[2] is None else row[2]
            outputs = 0 if row[3] is None else row[3]
            movement_list.append(tuple(
                (clients[row[1]], inputs, outputs, inputs
                 + outputs)))
    return movement_list


def load_file(movements, yesterday, folder):
    filename = 'pallet_movements ' + yesterday + '.csv'
    full_path = os.path.join(folder, filename)
    with open(full_path, mode='w', newline='') as pallet_movements:
        movements_writer = csv.writer(pallet_movements,
                                           delimiter=';')
        movements_writer.writerow(['Day: ' + yesterday])
        movements_writer.writerow(['Company', 'inputs', 'outputs',
                                       'Total'])
        for movement in movements:
            movements_writer.writerow(movement)
    return filename


def send_email(filename, yesterday, folder):
    sender = "*"
    destination = "*"
    msg = MIMEMultipart()
    msg['Subject'] = 'Pallet movements ' + yesterday
    msg['From'] = sender
    msg['To'] = destination
    message_text = 'Good morning,nnYou can find Pallet movements from
                      day ' + yesterday + ' attached.nnGoodbye'
    msg.attach(MIMEText(message_text))
    full_path = os.path.join(folder, filename)
    attachment = MIMEApplication(open(full_path, 'rb').read())
    attachment.add_header('Content-Disposition', 'attachment',
                        filename=filename)
    msg.attach(attachment)
    try:
        with smtplib.SMTP('*', 587) as smtpObj:
            smtpObj.ehlo()
            smtpObj.starttls()
            smtpObj.login("*", "*")
            smtpObj.sendmail(sender, destination, msg.as_string())
    except Exception as e:
        print(e)


def main():
    yesterday = date.today() - timedelta(days=1)
    yesterday = yesterday.strftime(f'%d-%m-%Y')
    local_folder = os.path.dirname(os.path.abspath(__file__))
    clients = load_clients()
    movements = load_movements(clients)
    filename = load_file(movements, yesterday, local_folder)
    send_email(filename, yesterday, local_folder)


if __name__ == "__main__":
    main()