Python file write issue with Pandas - python-3.x

Question

i wrote this python script to search for unseen mail in a mailbox, download xlsx attachment, make some modification on it and then post them to another service.
All is working perfect with just one issue:
In the original xlsx file there is a column named "zona" containing the italian two letter string for the province.
If this value is "NA" (the value of the province of NAPLES) when
saving the resultant xlsx files has blank cell instead of NA.
is NA a reserved word and if yes, there is a way to quote it?
import os,email,imaplib,socket,requests
import pandas as pd
mail_user = os.environ.get('MAIL_USER')
mail_password = os.environ.get('MAIL_PASS')
mail_server = os.environ.get('MAIL_SERVER')
detach_dir = '.'
url=<removed url>
if mail_user is None or mail_password is None or mail_server is None:
print ('VARIABILI DI AMBIENTE NON DEFINITE')
exit(1)
try:
with imaplib.IMAP4_SSL(mail_server) as m:
try:
m.login(mail_user,mail_password)
m.select("INBOX")
resp, items = m.search(None, "UNSEEN")
items = items[0].split()
for emailid in items:
resp, data = m.fetch(emailid, "(RFC822)")
email_body = data[0][1] # getting the mail content
mail = email.message_from_bytes(email_body) # parsing the mail content to get a mail object
if mail.get_content_maintype() != 'multipart':
continue
for part in mail.walk():
if part.get_content_maintype() == 'multipart':
continue
if part.get('Content-Disposition') is None:
continue
filename = part.get_filename()
if filename.endswith('.xlsx'):
att_path = os.path.join(detach_dir, filename)
fp = open(att_path, 'wb')
fp.write(part.get_payload(decode=True))
fp.close()
xl = pd.ExcelFile(att_path)
df1 = xl.parse(sheet_name=0)
df1 = df1.replace({'\'':''}, regex=True)
df1.loc[df1['Prodotto'] == 'SP_TABLETA_SAMSUNG','Cod. ID.'] = 'X'
df1.loc[df1['Prodotto'] == 'AP_TLC','Cod. ID.'] = 'X'
df1.loc[df1['Prodotto'] == 'APDCMB00003','Cod. ID.'] = 'X'
df1.loc[df1['Prodotto'] == 'APDCMB03252','Cod. ID.'] = 'X'
writer = pd.ExcelWriter(att_path, engine='xlsxwriter')
df1.to_excel(writer, sheet_name='Foglio1', index=False)
writer.save()
uf = {'files': open(att_path, 'rb')}
http.client.HTTPConnection.debuglevel = 0
r = requests.post(url, files=uf)
print (r.text)
except imaplib.IMAP4_SSL.error as e:
print (e)
exit(1)
except imaplib.IMAP4.error:
print ("Errore di connessione al server")
exit(1)

Answer 1

It seems that Pandas is treating the NA value as a NaN and therefore, when you write to excel it writes this value as '' by default (see docs).
You can pass na_rep='NA' to the to_excel() function in order to write it out as a string;
df1.to_excel(writer, sheet_name='Foglio1', index=False, na_rep='NA')
But as a precaution keep an eye out as any other NaN values present in your df will also be written to the excel file as 'NA'.

Answer 2

Reading the docs link post by #Matt B. i found this solution:
df1 = xl.parse(sheet_name=0, keep_default_na=False, na_values=['_'])
If i understand well only _ are interpreted as "not avalaible"