input: Write a function to convert a given SQL query into a Python equivalent using SQLite. The function should take an SQL query as input and return the result of executing the query on a SQLite database. If the database file named 'movies.db' does not exist, the function should return an error message instead. Include assertions to test the function with different SQL queries and expected outputs.
  assert sql_to_python("SELECT * FROM Movies WHERE category = 'horror'") == [expected_output_1]
  assert sql_to_python("SELECT title FROM Movies WHERE year > 2000") == [expected_output_2]
  assert sql_to_python("SELECT * FROM NonExistentTable") == "Database or table does not exist"
  assert sql_to_python("") == "Empty query provided"
output: import sqlite3
  
  def sql_to_python(query):
      if not query:
          return "Empty query provided"
      try:
          conn = sqlite3.connect('movies.db')
          cursor = conn.cursor()
          cursor.execute(query)
          result = cursor.fetchall()
          conn.close()
          return result
      except sqlite3.OperationalError as e:
          if 'no such table' in str(e) or 'no such database' in str(e):
              return "Database or table does not exist"
          else:
              return str(e)