which column of sql table is equal to a variable

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i want to find the value of 'vazn' (one column of sql table) where 'id' column is equal to f1.
f1 is a variable as following:
f1=int(enter3.get())
enter3 is an entry.
i entered the variable in enter3 that is equal to one of the existing 'id's in the sql table('bills')
this is my code:

Output:
[self.cur.execute("SELECT vazn FROM billse WHERE id1='f1'")
                vaznp = self.cur.fetchall()
                print(vaznp)][/python]

i get 'null' when it prints vaznp

why?????
please helpppp