For starters, it is probably best for security purposes to use os.getlogin() to determine the user's login name rather than prompting the user to type their username. This will at least guarantee that the user logged in via some authentication mechanism to get onto the system, meaning that they have a known & consistent username.
So if you wanted to turn this into a function you could write:
def is_valid_user(username):
fp = open("users", "r")
for line in fp.readlines():
if username in line:
fp.close()
return True
fp.close()
return False
You could then call the function using:
import os
is_valid = is_valid_user(os.getlogin())
if is_valid:
print("valid user")
else:
print("invalid user")
Some suggestions for added security now and in the future:
- Modify your "users" file to contain names surrounded by delimiters such as ":jonesj:" rather than "jonesj" and search for
":" + username + ":" in line which will avoid false positives in situations where a user "jones" is currently logged in and a username "jonesj" is in your "users" file but "jones" is not, and you incorrectly identify "jones" as being an authorized user (since "jones" is a subset of the string "jonesj").
- Make sure the permissions on your "users" file is set to read-only so that users can't go add their username to the file to grant permissions to themselves.
- Sometime in the future you may want to consider using LDAP or Kerberos server or some other more formal authentication mechanism rather than a "users" file. There are good python client libraries for quite a number of authentication backend servers.
