# Draw a Koch snowflake
from turtle import *
def koch(a, order):
if order > 0:
for t in [60, -120, 60, 0]:
forward(a/3)
left(t)
else:
forward(a)
# Test
koch(100, 0)
pensize(3)
koch(100, 1)

Now, we make a small change to the function koch:

for t in [60, -120, 60, 0]:
koch(a/3, order-1)
left(t)

Completed code:

# Choose colours and size
color("sky blue", "white")
bgcolor("black")
size = 400
order = 0
# Ensure snowflake is centred
penup()
backward(size/1.732)
left(30)
pendown()
# Make it fast
tracer(100)
hideturtle()
begin_fill()
# Three Koch curves
for i in range(3):
koch(size, order)
right(120)
end_fill()
# Make the last parts appear
update()

Source.