What if you want to specify a different price floor every time you run the search? What if you didn't want to use a floor but specify the price exactly? What if you wanted to reuse part of the statement and automate queries by fish name instead of retrieving all of them at once? Under such circumstances, you need to be able to handle variables in your SELECT statements.

MySQL for Python passes variables to MySQL in the same way that Python formats other kinds of output. If we wanted to specify just the floor of the search, we would assign the variable as any other and pass it to the execute() method as a string. Consider the following snippet from a Python terminal session:

>>> value = "7.50"
>>> command = cur.execute("""SELECT * FROM menu WHERE price = %s""" %(value))
>>> results = cur.fetchall()
>>> for record in results:
... print record[0], ". ", record[1], "(%s)" %record[2]
... 
1 . tuna (7.50)

If we wanted the user to have the option of specifying the price precisely or using comparative expressions, we can add in that option along with making the previous variable user-defined.

>>> operation = input("operation: ")
operation: '='
>>> value = input("value: ")
value: 7.50
>>> command = cur.execute("""SELECT * FROM menu WHERE price %s %s""" %(operation, value))
>>> results = cur.fetchall()
>>> for record in results:
... print record[0], ". ", record[1], "(%s)" %record[2]
... 
1 . tuna (7.50)

As you may have surmised by now, the execute() method is simply passing the MySQL statement as a string to _mysql, which in turn passes it to the C database API, which in turn passes it to MySQL. This being the case, we can define the statement separately and pass it to execute() as a variable. Consider the following replacement for the latter half of the preceding code.

>>> statement = """SELECT * FROM menu WHERE price %s %s""" %(operation, value)
>>> command = cur.execute(statement)
>>> results = cur.fetchall()
>>> for record in results:
... print record[0], ". ", record[1], "(%s)" %record[2]
... 
1 . tuna (7.50)