Experiments with Pexpect

The Pexpect python module is used to start up and control new processes from python code.  For the Manchester CoderDojo I needed to incrementally get output from a spawned process over the course of a long run.  To test this I created a simple module that counted to 20 slowly:

"""
Count to 20 in one second steps
"""
from time import sleep

for i in range(1,21):
    print(str(i))
    sleep(1)

Next I created a python module to spawn off a process to call the counter and print the output.

"""
Call the slow-running counter and print the results.
"""

import pexpect

output = pexpect.run('python count-slow.py')
print(output)

The problem of course is that the run command blocks until all the output is produced.  The solution allowing you to  see the output as it appears is to use the pexpect.spawn() function.  This function to creates a sub-process object from which you can read one line at a time.  Pyexpect.readline() will block until it receives a line.  An empty string indicates the process has completed.

"""
Call the slow-running counter and print the results.
"""

import pexpect

child = pexpect.spawn('python count-slow.py')
next_line = child.readline()
while next_line != '':
    print(next_line.strip())
    next_line = child.readline()

Formatting Python Code for the Web with Pygments

I've been unsatisfied with Blogger's lack of easy handling for code formatting.  To fix this I installed Pygments.  I can now type,

pygmentize -f html -O noclasses count-slow.py

...and end up with output that I can paste into the Blogger HTML editor window.

The result is something like this:

"""
Count to 20 in one second steps
"""
from time import sleep

for i in range(1,20):
    print(str(i))
    sleep(1)

Vagrant Working for the Manchester CoderDojo Minecraft Server Build

I've got a basic vagrant setup working for the Manchester CoderDojo Minecraft server build.  Instructions on the GitHub page.

Next task is to get the chunked responses working so that you can see the python output appear in the browser as the code is running.

Tip: Copying Large Files from Remote Desktop Sessions

I just had the problem of having to grab a large file from a Windows remote desktop session.  The usual cut-remote-paste-local magic wasn't going to manage the file size.  It turns out that RDP maps "\\TSCLIENT\" on the remote server to your local PC.  You can therefore use robocopy to bring the large file over locally using the restart mode in case of problems. 

For example to grab "big file.zip" from the current folder on the remote box to the c:\tmp folder locally run this:

robocopy /z /eta .  \\TSCLIENT\C\tmp "big file.zip"