How to add command line arguments with flags in Python3?

Question

I have to input the parameters from the command line i.e username, password, and database name. I know how to do that without using flags, by using sys.argv like below:

##Test.py
hostname = str(sys.argv[1])
username = str(sys.argv[2])
password = str(sys.argv[3])

def ConnecttoDB():
    try:
        con=sql.connect(host=hostname, user= username, passwd= password)
        print ('\nConnected to Database\n')

# If we cannot connect to the database, send an error to the user and exit the program.
    except sql.Error:
        print ("Error %d: %s" % (sql.Error.args[0],sql.Error.args[1]))
        sys.exit(1)

    return con   

So, it could be run as:

$test.py DATABASE USERNAME PASWORD

But the problem is that I have to use 'flags'. So, the script could be run like this:

$test.py -db DATABSE -u USERNAME -p PASSWORD -size 20

How can I use flags to take arguments from the command line?

Answer 1

The python 3 library includes 3 modules for parsing the command line thus nothing extra to add to your setup.

The one you should use is argparse

import argparse
parser = argparse.ArgumentParser()

#-db DATABSE -u USERNAME -p PASSWORD -size 20
parser.add_argument("-db", "--hostname", help="Database name")
parser.add_argument("-u", "--username", help="User name")
parser.add_argument("-p", "--password", help="Password")
parser.add_argument("-size", "--size", help="Size", type=int)

args = parser.parse_args()

print( "Hostname {} User {} Password {} size {} ".format(
        args.hostname,
        args.username,
        args.password,
        args.size
        ))