Declaring a variable in postgres from python

I have a variable whose value is set by the user each time the person runs a query. I am running this script in python which then makes a call to a postgres database. I am hoping to first assigning a value to the variable in one piece of sql code and then I am hoping to call that variable in a second piece of sql code.

Here is my current code:

First my code to set the postgres variable:

sql_stateVar=(""" 
                  tempState VARCHAR:= %s
              """
              ,(stateVar,))
cur.execute(*sql_stateVar)

Then with this variable set in postgres, I am going to call this stored variable:

sqlquery=("""
    SELECT UPPER(b.state) AS state,
    FROM opentable_full b
    WHERE UPPER(b.state)=UPPER(tempState)
    GROUP BY UPPER(b.state)
""")

Then I have the following code:

    outputquery = "COPY({0}) TO STDOUT WITH CSV HEADER".format(sqlquery)

    with open('resultsfile', 'w') as f:
        cur.copy_expert(outputquery, file=f)

I have seen several answers regarding the limitations of setting variables in postgres, but as I am new to postgres, I am not sure if these answers are what I need.

For example: Is there a way to define a named constant in a PostgreSQL query?
AND
How to declare local variables in postgresql?