sql.py

from sqlalchemy.sql import text, select, join
def wrap_array_for_columns(arr):
    return map(lambda x: text(column_text(x)), arr)

def column_text(column_struct):
    _name = column_struct.get("name")
    _table = column_struct.get("table")
    _alias = column_struct.get("alias", _name)
    if _table is None:
        return "%s as %s"%(_name, _alias)
    return "%s.%s as %s"%(_table, _name, _alias)

a = 'restaurant_from_df'
b = 'restaurant_cross'
c = 'restaurant_from_json'
grade_json = 'json_array_elements(grades_json::json) grade'

s = select(wrap_array_for_columns(
    [{"name": "grade->>'score'", "alias": "score"},
     {"name": "name", "table": a}
    ]), 
    from_obj=[join(
        join(text(a),text(b),text('%s.restaurant_id=%s.restaurant_id'%(a,b))),
        text(c), text('%s.restaurant_id=%s.restaurant_id'%(a,c))
    ),text(grade_json)]) \
    .limit(text('10'))
select3 = str(s)
print(select3)