Working with time.process_time()

Question

I'm trying to time how long a sort function takes, but I am struggling getting time.process_time() to work.

My current setup is:

start = time.process_time()
insertionsort(n)
end = time.process_time()

time = start-end

When I run this, I am getting this error:

'float' object has no attribute 'process_time'

How do I fix this problem? I want to use time.process_time().

Solution

The issue is in a part of the code that you didn't show. I assume that you imported the time module in the beginning:

import time

Which creates a name time that references the time module.

But later you create a variable named time that stores the time difference. At that point the name time references the difference and not the module. So when you try to use time.process_time() afterwards you get the Error.

This simple snippet illustrates the problem:

>>> import time
>>> time = -(time.process_time() - time.process_time())
>>> time.process_time()
AttributeError: 'float' object has no attribute 'process_time'

If you insist on using time.process_time() the best way around would be to rename the variable that stores the time difference:

measured_execution_time_insertionsort = end - start

But you could also import the process_time function from the time module directly:

from time import process_time

start = process_time()
insertionsort(n)
end = process_time()

time = end - start

Both approaches avoid the name clash. However I would recommend you use the timeit module if you want to measure executions times, it's better suited for this kind of task than the time module.

Comments

[Amit Tripathi]

This is the issue. time = start-end don't name your variable with the same name as standard library.

[Thomas S.]

To get a positive time answer will you need to make it time = end - start instead of time = start - end

[MSeifert]

@ThomasS. Yeah, I originally copied that from the question. However having a positive result seems obviously correct so I updated the answer. Thanks for pointing this out.

[Nike]

After running import time and time = -(time.process_time() - time.process_time()) I get Traceback (most recent call last): File "<stdin>", line 1, in <module>. Maybe because I'm using Python 2.7.12 (default, Mar 1 2021, 11:38:31)? If I try to do from time import process_time I get: Traceback (most recent call last): File "<stdin>", line 1, in <module> ImportError: cannot import name process_time

[MSeifert]

@user1271772 Yeah, it's because you are using Python 2. That feature isn't implemented there.