import psycopg2

try:
    conn = psycopg2.connect("dbname='XXX' user='XXX' host='XXX' password='XXX'")
except:
    print("No ha sido posible conectar a la base de datos")

conn.set_client_encoding('UTF8')
cur = conn.cursor()
cur.execute("""XXX""")
rows = cur.fetchall()
...

conn = connections['XXX']
cur = conn.cursor()
cur.execute("""XXX""")
rows = cur.fetchall()
...