Why isn't this code returning these lists? Does this have to do with using 'return' rather than 'print'?

问题

So this is my code, when I had everything set to 'print' things, the code worked, but now with 'return' the program terminates after I select a Subject, Topic, and the questions/answers. I made this program to enter in my flash card questions and answers, and then be able to select the subject, then select a topic, and then select whether to see only questions, answers, or see both. I noticed at the end of each list the word 'None' would appear, I tried to fix this by replacing 'print', with 'return', but that has brought up even more problems, I would really appreciate some input on what I should do.

Code is below

--Ethan, 13

import sys
subjects = ["History", "Science"]
topics_science = ["Light", "X-mas Exam Review"]
topics_history = ["Italian Renaissance"]
science_xmasreview = ["Q. What do we use to catogorize a habitat?", \
"A. Damp or Dry, Hot or Cold, Windy or Calm, Dim or Bright.", \
"Q. What is something that only eats plants?", \
"A. Herbivore", \
"Q. What are the properties of oxygen?"]

science_light = [
"Q. What is an object the gives out light?", \
"A. Light source", \
"Q. What is the speed of light?", \
"A. 300 million meters per second.", \
"Q. What does transparent mean?", \
"A. Light can pass completely through a transparent material."]

history_renaissance = [
"Q. What did Lorenzo do differently from Cosimo?", \
"A. Lorenzo made no effort to conceal his power", \
"Q. Why did the Pope want Lorenzo dead?", \
"A. Because the Pope wanted more power and saw Lorenzo as a threat.", \
"Q. Who did the Pazzi plot with to kill Lorenzo?", \
"A. Pope Sixtus IV"]

def qanda(x):
    print
    print "Enter 1 for just questions"
    print "Enter 2 for just answers"
    print "Enter 3 for both"
    qa = raw_input("Enter number: ")
    qa = str(qa)
    if qa == '1':
        printer(x[::2])
    elif qa == '2':
       printer(x[1::2])
    elif qa == '3':
        printer(x)
    else:
        print "Not recognized"
def newline():
    raw_input()
    print
def printer(list):
    n = 0
    l = len(list)
    print
    while n < l:
        return list[n]
        newline()
        n += 1
    while n == l:
        n += 1
def subjectchoice():
    if subject == "1":
        print
        history()
    elif subject == "2":
        print
        science()
        else:
        print 'Not recognized.'
def science():
    print topics_science
    print "Enter 1 for Light"
    print "Enter 2 for X-mas Exam Review"
    topicchoice = raw_input("Enter number: ")
    topicchoice = str(topicchoice)
    if topicchoice == "1":
        qanda(science_light)
    elif topicchoice == "2":
          qanda(science_xmasreview)
    else:
        print "Not recognized"
        sys.exit
def history():
    print topics_history
    print "Enter 1 for Italian Renaissance"
    topicchoice = raw_input("Enter number: ")
    topicchoice = str(topicchoice)
    if topicchoice == "1":
       return qanda(history_renaissance)
    else:
        print "Not recognized"
        sys.exit()
print subjects
print "Enter 1 for History"
print "Enter 2 for Science"
subject = raw_input("Enter number: ")
subject = str(subject)
subjectchoice()

回答1:

I believe this will work, you didn't need the return statement in your printer() function:

import sys
subjects = ["History", "Science"]
topics_science = ["Light", "X-mas Exam Review"]
topics_history = ["Italian Renaissance"]
science_xmasreview = ["Q. What do we use to catogorize a habitat?",
                      "A. Damp or Dry, Hot or Cold, Windy or Calm, Dim or Bright.",
                      "Q. What is something that only eats plants?",
                      "A. Herbivore",
                      "Q. What are the properties of oxygen?"]

science_light = [
    "Q. What is an object the gives out light?",
    "A. Light source",
    "Q. What is the speed of light?",
    "A. 300 million meters per second.",
    "Q. What does transparent mean?",
    "A. Light can pass completely through a transparent material."]

history_renaissance = [
    "Q. What did Lorenzo do differently from Cosimo?",
    "A. Lorenzo made no effort to conceal his power",
    "Q. Why did the Pope want Lorenzo dead?",
    "A. Because the Pope wanted more power and saw Lorenzo as a threat.",
    "Q. Who did the Pazzi plot with to kill Lorenzo?",
    "A. Pope Sixtus IV"]

def printer(list):
    n = 0
    l = len(list)
    print
    while n < l:
        print list[n]  # <-- Changed this from a return to a print statement
        newline()
        n += 1
    while n == l:
        n += 1

def qanda(x):
    print
    print "Enter 1 for just questions"
    print "Enter 2 for just answers"
    print "Enter 3 for both"
    qa = raw_input("Enter number: ")
    qa = str(qa)
    if qa == '1':
        printer(x[::2])
    elif qa == '2':
        printer(x[1::2])
    elif qa == '3':
        printer(x)
    else:
        print "Not recognized"

def newline():
    raw_input()
    print



def subjectchoice():
    if subject == "1":
        print
        history()
    elif subject == "2":
        print
        science()
    else:
        print 'Not recognized.'
def science():
    print topics_science
    print "Enter 1 for Light"
    print "Enter 2 for X-mas Exam Review"
    topicchoice = raw_input("Enter number: ")
    topicchoice = str(topicchoice)
    if topicchoice == "1":
        qanda(science_light)
    elif topicchoice == "2":
        qanda(science_xmasreview)
    else:
        print "Not recognized"
        sys.exit
def history():
    print topics_history
    print "Enter 1 for Italian Renaissance"
    topicchoice = raw_input("Enter number: ")
    topicchoice = str(topicchoice)
    if topicchoice == "1":
        return qanda(history_renaissance)
    else:
        print "Not recognized"
        sys.exit()
print subjects
print "Enter 1 for History"
print "Enter 2 for Science"
subject = raw_input("Enter number: ")
subject = str(subject)
subjectchoice()

来源：https://stackoverflow.com/questions/15465412/why-isnt-this-code-returning-these-lists-does-this-have-to-do-with-using-retu