Topic

For this assignment, I've written two multiple choice questions for Software Carpentry's Command-Line Programs lesson.

MCQ #1

Question

Suppose we write our own version of a line count program called my_line_count.py:

import sys

lc = 0
for line in sys.stdin:
    lc +=1

print lc, 'line(s)'

How can we get this program to return the number of lines in the file sample.txt?

1. python my_line_count.py sample.txt
2. python my_line_count.py > sample.txt
3. python my_line_count.py < sample.txt
4. python my_line_count.py | sample.txt

An alternative

After I wrote the above question, I thought that we could try to invert it so that it reads:

Suppose we write our own version of a line count program called my_line_count.py:

import sys

lc = 0
for line in sys.stdin:
    lc +=1

print lc, 'line(s)'

We have a file called sample.txt which has exactly 10 lines in it. We want to test our program with this file so we run the command

$ python my_line_count.py > sample.txt

This just moves the cursor down to the next line, which is not what we expected so we hit CTRL-D to get back to the command line. What happens next?

1. The python program prints the number of lines in sample.txt, i.e. 10 lines, to stdout.
2. The python program prints 0 lines to stdout.
3. The python program overwrites all of the data we had in sample.txt with the text 0 lines.
4. The shell gives us an error because sample.txt is not a command.

Both of these questions test the same material. In my opinion as a novice teacher, the first version is a little too simple and the second version is way too convoluted. So I'd probably err on the side of safety and use the first version, but I'd really like to get your thoughts in the comments section about how I could improve the first one by making it less leading.

MCQ #2

Question

Consider the following python program add_args.py:

import sys

print sys.argv[0] + sys.argv[1]

What should we expect as the output of the command

$ python add_args.py 5 3`

1. '53'
2. TypeError: cannot concatenate 'str' and 'int' objects
3. 8
4. 'add_args.py5'

Analysis of answers

The distractors in this question are:

1. The student understands that argv is a list of strings, but doesn't understand that argv[0] is script name.
2. The student understands that argv[0] is the script name but doesn't understand that all argv is a list of strings. So they expect the second argument to be interpreted as an int.
3. The student understands neither that argv is a list of strings, nor that argv starts with the script name.