python中文注释问题

[wu@server python]$ cat ex4.py
#!/usr/bin/python

#中文注释
#cars_num
cars = 100
#space_car_num
space_in_a_car = 40
drivers = 30
passengers = 90
cars_not_driven = cars - drivers
cars_driven = drivers
carpool_capacity = cars_driven * space_in_a_car
average_passengers_per_car = passengers / cars_driven

print "There are", cars, "cars available."
print "There are only", drivers, "drivers available."
print "There will be", cars_not_driven, "empty cars today."
print "We can transport", carpool_capacity, "people today."
print "We have", passengers, "to carpool today."
print "We need to put about", average_passengers_per_car, "in each car."
[wu@server python]$ ./ex4.py
File "./ex4.py", line 3
SyntaxError: Non-ASCII character '\xe4' in file ./ex4.py on line 3, but no encoding declared; see http://www.python.org/peps/pep-0263.html for details

[wu@server python]$ cat ex4.py
#!/usr/bin/python
# -*- coding:utf-8 -*-

#中文注释
#cars_num
cars = 100
#space_car_num
space_in_a_car = 40
drivers = 30
passengers = 90
cars_not_driven = cars - drivers
cars_driven = drivers
carpool_capacity = cars_driven * space_in_a_car
average_passengers_per_car = passengers / cars_driven

print "There are", cars, "cars available."
print "There are only", drivers, "drivers available."
print "There will be", cars_not_driven, "empty cars today."
print "We can transport", carpool_capacity, "people today."
print "We have", passengers, "to carpool today."
print "We need to put about", average_passengers_per_car, "in each car."
[wu@server python]$ ./ex4.py
There are 100 cars available.
There are only 30 drivers available.
There will be 70 empty cars today.
We can transport 1200 people today.
We have 90 to carpool today.
We need to put about 3 in each car.
[wu@server python]$