[ Python 常見問題 ] Python speed testing - Time Difference - milliseconds

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Question 
What is the proper way to compare 2 times in Python in order to speed test a section of code? I tried reading the API docs. I'm not sure I understand thetimedelta thing. So far I have this code: 

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1. from datetime import datetime  
2.   
3. tstart = datetime.now()  
4. print t1  
5.   
6. # code to speed test  
7.   
8. tend = datetime.now()  
9. print t2  
10. # what am I missing?  
11. # I'd like to print the time diff here  

How-To 
datetime.timedelta is just the difference between two datetimes ... so it's like a period of time, in days / seconds / microseconds: 

>>> import datetime
>>> a = datetime.datetime.now()
>>> b = datetime.datetime.now()
>>> c = b - a

>>> c
datetime.timedelta(0, 4, 316543)
>>> c.days
0
>>> c.seconds
4
>>> c.microseconds
316543

Be aware that c.microseconds only returns the microseconds portion of the timedelta! For timing purposes always use c.total_seconds(). You can do all sorts of maths with datetime.timedelta, eg: 

>>> c / 10
datetime.timedelta(0, 0, 431654)

It might be more useful to look at CPU time instead of wallclock time though ... that's operating system dependant though ... under Unix-like systems, check out the 'time' command.