Python嵌入式Linux命令

Question

I am testing sorting algorithms and therefore I would like to compine in my Python code, the linux command "time", because it takes some interesting arguments and for example the call of quicksort.

from subprocess import Popen
import quicksort
import rand

time=Popen("time quicksort.main(rand.main())")

This is tottaly wrong, but it is the closest I managed to get. I haven't grasped the idea of subprocess class, is it possible to combine method calls with linux commands, or only add commands in python like "grep..." and send the output to a variable??

Answer 1

If you use Popen from subprocess you need to do a lot of things differently.

I believe what you are looking for is check_output, another function belonging to the subprocess module.

But in order to further your understanding, since you are sort-of close, here is what you need to change to get it to work:

The command string "time quicksort.main(rand.main())" is not going to mean anything to bash. That is python. BUT in the case that it was valid bash language, it would need to be split on word boundaries (like bash WOULD normally do) so you would make it into a list:

['time', '...','...']

The only time you can pass Popen a command STRING (not a list) is when you set shell=True in the keywords to Popen.

But let's just leave shell at False, do some word-splitting for bash, and pass in a list. On to the next part.

Popen returns something you can communicate to/at/with. Not the result of the process' stdout. Use subprocess.PIPE for stdin and stdout keywords to Popen.

Once you have made a Popen object as described, you can call it's communicate method.

The result is two things, stdout and stderr.

You're after the first one. One use case for Popen is for when you need to keep errors and output seperate. Obviously this isn't turning out to be the best option for inline but oh well. Lets deal with stdout.

sdtout will probably need to be decoded:

stdout.decode()

or perhaps even have newlines stripped as well:

stdout.decode().rstrip()

So as you can see, Popen does not fit the use case you have in mind. There is no need to use subprocess and make system calls in order to time python. Look into timeit .