Tutorial Moodle VPL Gremlins -- Python

--D. Thiebaut (talk) 12:33, 11 June 2014 (EDT)

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This tutorial builds on the first one in the series, which should be done first, as the present tutorial skips some steps. In this tutorial we setup a VPL activity that tests a Python program that is supposed to

1. ask the user for the name of a file (that must exists)
2. open the file, read it, and replace all g- and G-letters with gremlin or Gremlin, and
3. save the new content in the original file.

We perform the evaluation and automatic grading of the program by using a second Python program that creates the sample text file and feeds its name via a redirected stdin to the student program.

VPL Activity Description: Version 1

runGremlin.py

This program is provided and should NOT be modified by the student.

#runGremlin.py
# students, do not modify this file.  It will be used to test
# your program.  Instead, copy/paste or enter your code in 
# gremlin.py (next tab over)
import sys

#--- create a sample text file to use in the test ---
file = open( "sample.txt", "w" )
file.write( """Great news!
The eggs are greatly reduced today.
Good day!
""" )
file.close()

#--- put the name of the sample file into another text file that
#--- will serve as stdin for the program to test
file = open( "fakestdin.txt", "w" )
file.write( "sample.txt\n" )
file.close()

#--- make stdin read information from the text file
file = open( "fakestdin.txt", "r" )
sys.stdin = file

#--- capture the stdout of the program to test into a file
saveStdOut = sys.stdout
sys.stdout = open( "fakestdout.txt", "w" )

#--- run the program to test ---
import gremlin

#--- get rid of whatever it printed on the stdout ---
sys.stdout = saveStdOut

#--- display the contents of the sample.txt file which should 
#--- have been modified by the program under test.
file = open( "sample.txt", "r" )
print( file.read(), end="" )
file.close()

gremlin.py

This is the program that the student must complete.

# Enter your code below (and remove this line!)

Execution files

vpl_run.sh

#! /bin/bash
 
echo "#! /bin/bash"  > vpl_execution
echo "python3.4 runGremlin.py" >> vpl_execution
chmod +x vpl_execution

vpl_evaluate.cases

case = Test 1

output = "Gremlinreat news!
The egremlingremlins are gremlinreatly reduced today.
Gremlinood day!
"

Testing

• In the VPL Administration box, click on Test activity, Edit, and enter this code for gremlin.py:

# Enter your code below (and remove this line!)
fileName=input( "File name? " )
file = open( fileName, "r" )
text = file.read()
file.close()

text = text.replace( 'g', 'gremlin' )
text = text.replace( 'G', 'Gremlin' )

file = open( fileName, "w" )
file.write( text )
file.close()

• Click on Evaluate and verify that the program passes the test.

VPL Activity Description: Version 2

In this version the runGremlin.py program is hidden from the student and included in the Execution files of the VPL maintenance module.

• Set the number of files the student has to upload to 1, and make the file name gremlin.py. In the Execution files window of the VPL maintenance module, add a new file along with vpl_run.sh, vpl_debug.sh, vpl_evaluate.sh, and vpl_evaluate.cases: runGremlin.py.
• Set its contents to the same contents as in Version 1 above.
• The vpl_run.sh does not change, and still reads:

#! /bin/bash
 
echo "#! /bin/bash" > vpl_execution
echo "python3.4 runGremlin.py" >> vpl_execution
chmod +x vpl_execution

The adventage of this method is that the student is unaware that there is a second python program, and therefore has fewer chances of getting confused.

This concludes this tutorial