Python MySQLdb substituting strings into mysql conn

Question

I have a connection line as below and I want to substitute in variables, but cannot get it to work:

db = MySQLdb.connect(host="localhost", user="root", passwd="password", db="database")

I change this to use a variable:

db = MySQLdb.connect(host="localhost", user="%s", passwd="password", db="database") % "root"

Error: mysql_exceptions.OperationalError: (1045, "Access denied for user '%s'@'localhost' (using password: YES)")

So, it is not substituting and tries to run the query with %s. I also tried with a .format (instead of %s) and got the same issue.

To get around this, I was going to substitute the line beforehand and then add in the connection line as one argument, however even a basic version of this doesn't work for me. Here is a trial run, but it fails even without any substituation:

variable = '''MySQLdb.connect(host="localhost", user="root", passwd="password", db="database")''' 
db = MySQLdb.connect(variable)

This results in mysql trying to pass the entire variable as the first argument (the host): _mysql_exceptions.OperationalError: (2005, 'Unknown MySQL server host \'host="localhost", user="root", passwd="password", db="database"\' (2)')

While Daniel's answer is definitely correct and to be preferred, the actual mistake you made here is this: You're dealing with 4 strings here (used as keyword arguments). You would need to apply the substitution to the individual string(s) for your approach to work, like this: MySQLdb.connect(host="localhost", user="%s" % "root", passwd="password", db="database-%s" % n) — Lukas Graf
– Lukas Graf, Commented Sep 30, 2015 at 12:32
@LukasGraf thanks for the clarification. I had considered that but didn't try it since it looked like something that would throw an error fi I had % "root" in the middle of the command. Guess not. — derpy
– derpy, Commented Sep 30, 2015 at 12:39

Daniel Roseman · Accepted Answer · 2015-09-30 12:17:53Z

4

I think you're over thinking this. This is a standard function call, and has nothing at all that is specific to MySQLdb. As with any call, if you want to use a variable, you just do so:

user = 'root'
MySQLdb.connect(host="localhost", user=user, passwd="password", db="database")

answered Sep 30, 2015 at 12:17

Daniel Roseman

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