# (A) LOAD CSV MODULE
import csv

# (B) READ EXISTING ROWS INTO A LIST
with open("demo.csv", "r", newline="") as csvfile:
  rows = list(csv.reader(csvfile))

# (C) PREPEND NEW ROWS
rows = [["G", "H"], ["I", "J"]] + rows

# (D) SAVE UPDATED CSV
with open("demo.csv", "w", newline="") as csvfile:
  writer = csv.writer(csvfile)
  writer.writerows(rows)