My code neither produces output nor an error, code looks correct, how to troubleshoot with no output?

Question

I'm trying to solve Ex 41 from Zed Shaw's "Learn Python the Hard Way". I have created the file for it. The exercise retrieves a text file from the author's website. When I run it on the command line (Ubuntu) it just kicks me back to the prompt with no visible output.

I'm not sure how to identify what the problem is. I have tried:

• Checking the code carefully. The code looks identical to the book as far as I can tell.

• Running it in IDLE instead, produces no output, just returns to the prompt

• Running python with -v (which didn't produce anything)

• Changing the URL to https, and

• Verifying that the word list is available at that URL (it is).

Any other python exercise I have still runs fine. Is there a way to see more output (like a log file, or a method of forcing more output) where I can try to figure out what is going on?

import random
from urllib import urlopen
import sys

WORD_URL = "https://learncodethehardway.org/words.txt"
WORDS = []

PHRASES = {
    "class %%%(%%):":
      "Make a class named %% that is-a %%.",
    "class %%(object):\n\tdef_init_(self, ***)" :
      "class %% has-a _init_ that takes self and *** parameters.",
    "class %%(object):\n\tdef ***(self, @@@)":
      "class %%% has-a function named *** that takes self and @@@ parameters.",
    "*** = @@@()":
      "Set *** to an instance of class %%%.",
    "***.***(@@@)":
      "From *** get the *** function, and call it with parameters self, @@@.",
    "***.*** = '***'":
      "From *** get the *** attribute and set it to '***'."
}

#do they want to drill phrases first
PHRASE_FIRST = False
if len(sys.argv) == 2 and sys.argv[1] == "english":
    PHRASE_FIRST = True

#load up words from the website
for word in urlopen(WORD_URL).readlines():
    WORDS.append(word.strip())


def convert(snippet, phrase):
    class_names = [w.capitalize() for w in
                    random.sample(WORDS, snippet.count("%%"))]
    other_names = random.sample(WORDS, snippet.count("***"))
    results = []
    param_names = []

    for i in range(0, snippet.count("@@")):
        param_count = random.randint(1,3)
        param_names.append(', '.join(random.sample(WORDS, param_count)))

    for sentence in snippet, phrase:
        result = sentence[:]

        #fake class class_names
        for word in class_names:
            result = result.replace("%%%", word, 1)

        #fake other names
        for word in other_names:
            result = result.replace("***", word, 1)

        #fake parameter lists
        for word in param_names:
            result = result.replace("@@@", word, 1)

            results.append(results)

        return results


    # keep going until they hit ctrl-D
    try:
        while True:
            snippets = PHRASES.keys()
            random.shuffle(snippets)

            for snippet in snippets:
                phrase = PHRASES[snippet]
                question, answer = convert(snippet, phrase)
                if PHRASE_FIRST:
                    question, answer = answer, question

                print question

                raw_input("> ")
                print "ANSWER: %s\n\n" % answer
    except EOFError:
        print "\nBye"

Answer 1

As jasonharper has mentioned, your prints are called inside convert which is not called at all.

If you're looking for a more general method of debugging for something not happening (let's imagine that you have some really big and complicated script), I can suggest you the following one:

• put print "start" in the beginning of your script and print "end" before the instruction that doesn't seem to be handled
• run the script to check whether it's ok with your environment (you should see "start" in the output – but if you, say output into a file, then you'll have to change that or monitor the file instead) and whether python doesn't actually come to the instruction of interest (you shouldn't see "end" – otherwise something's wrong with the instruction itself)
• now start moving print "end": once at a time, move it out of conditional block or loop or move to first line of function definition or from the function definition to the place where it's called. At some point you'll either see that the "end" output appear (in that case check the condition of the block or return statements inside the function other things that can prevent you from getting to the position where you had print "end" previously); or, like in your example, you'll notice that the call is not in your program at all
• in some cases, it can be useful to move print "start" instead or besides print "end" – but idea is the same: you moving those closer to each other and look for a moment when "start is shown, end is not" situation changes