How to use variables in SQL statement in Python?


Question

Ok so I'm not that experienced in Python.

I have the following Python code:

cursor.execute("INSERT INTO table VALUES var1, var2, var3,")

where var1 is an integer, var2 & var3 are strings.

How can I write the variable names without python including them as part of the query text?

1
78
10/16/2015 9:22:11 AM

Accepted Answer

cursor.execute("INSERT INTO table VALUES (%s, %s, %s)", (var1, var2, var3))

Note that the parameters are passed as a tuple.

The database API does proper escaping and quoting of variables. Be careful not to use the string formatting operator (%), because

  1. it does not do any escaping or quoting.
  2. it is prone to Uncontrolled string format attacks e.g. SQL injection.
81
3/19/2015 2:17:03 PM

Different implementations of the Python DB-API are allowed to use different placeholders, so you'll need to find out which one you're using -- it could be (e.g. with MySQLdb):

cursor.execute("INSERT INTO table VALUES (%s, %s, %s)", (var1, var2, var3))

or (e.g. with sqlite3 from the Python standard library):

cursor.execute("INSERT INTO table VALUES (?, ?, ?)", (var1, var2, var3))

or others yet (after VALUES you could have (:1, :2, :3) , or "named styles" (:fee, :fie, :fo) or (%(fee)s, %(fie)s, %(fo)s) where you pass a dict instead of a map as the second argument to execute). Check the paramstyle string constant in the DB API module you're using, and look for paramstyle at http://www.python.org/dev/peps/pep-0249/ to see what all the parameter-passing styles are!


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