# (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) INSERT BEFORE "JON DOE"
at = 0
for i, r in enumerate(rows):
  if "Jon Doe" in r:
    at = i
    break

# (D) INSERT NEW ROWS
rows.insert(at, ["M", "N"])

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