pymongo specify variable in connection string
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I am using pymongo to connect to my mongodb database. I am trying to call the database name and collection name in the connection string but I can't figure it out. 

If I have a database name (mydb) and a collection named (mycol) this example works:

    con = Connection('mymongodbhost')
    d = con.mydb.mycol.find_one()
    print (d)

That works fine but lets say I am defining mydb and mycol as variables, how do I call them in the connection string. So lets say I have:

    db = parser.get('some_conf_file', 'db_name')
    col = parser.get('some_conf_file', 'col_name')

How do I specify the db and col variables (which work that is just a code snippit) in my connection string? I've tried all sorts of combinations, and this certainly doesn't work:

    d = con.db.col.find_one()
    print (d)

This basically is calling the db (db) and the collection (col). But I want the variable values replaced by db and col in the example above. 

Thanks.