While Loop With Yes/No Input (Python)

问题

I am building a script to plot smooth and plot values. However, I am having trouble getting the yes/no function to control the while loop.

I am setting the while condition equal to "N" and waiting for the user to say they like the plotting (input of Y) before exiting.

I am getting a "NameError: name 'reply' is not defined."

import matplotlib.pyplot as plt
import numpy

while True:
    reply[0] = 'n'
    def yes_or_no(question):
        reply = str(input(question+' (y/n): ')).lower().strip()
        if reply[0] == 'y':
            return 1
        if reply[0] == 'n':
            return 0
        else:
            return yes_or_no("Please Enter (y/n) ")

# a bunch of math
# plots for the user

yes_or_no('Do you like the plot')
break
print("done")

When I adjusted reply[0] to reply the program hangs (see below)

print("started")
while True:
    reply = 'n'
    def yes_or_no(question):
        reply = str(input(question+' (y/n): ')).lower().strip()
        if reply[0] == 'y':
            return 1
        if reply[0] == 'n':
            return 0
        else:
            return yes_or_no("Please Enter (y/n) ")

yes_or_no('Do you like the plot')
print("done")

回答1:

Try:

def yes_or_no(question):
    reply = str(input(question+' (y/n): ')).lower().strip()
    if reply[0] == 'y':
        return 1
    elif reply[0] == 'n':
        return 0
    else:
        return yes_or_no("Please Enter (y/n) ")

print("started")
while True:
    # DRAW PLOT HERE;
    print("See plot....")
    if(yes_or_no('Do you like the plot')):
        break
print("done")

Best to keep function definition separate from loop for clarity. Also, otherwise it will be read in every loop wasting resources.

Output:

$ python ynquestion.py 
started
See plot....
Do you like the plot (y/n): n
See plot....
Do you like the plot (y/n): N 
See plot....
Do you like the plot (y/n): NO
See plot....
Do you like the plot (y/n): No
See plot....
Do you like the plot (y/n): no
See plot....
Do you like the plot (y/n): yes
done
$

回答2:

You should definitely look at some tutorials about "how to code" in general. There are several "misconceptions". However, here is a cleaner version:

import matplotlib.pyplot as plt
import numpy

def bunch_of_math():
    ...

def plotting():
    ...

# move this into the loop in case you want to calc and plot
# new stuff every iteration
bunch_of_math()
plotting()

print("start")

while True:
    reply = str(input(question+' (y/n): ')).lower().strip()
    if reply == 'y':
        break
    elif reply == 'n':
        break
    else:
        print("please select (y/n) only")
        continue

print("done")

It is bad style to declare a function inside a loop, especially if you do not need this. Your code would re-create the function at each iteration, which you would only need if you somehow alter your function in each iteration.

reply[0] = 'n' means that you want to access the list or array (a container data structure) reply with the index 0 and write 'n' there. You have not initialized such a container. Additionally, you do not need a container at all, because you do not store each user input. You just care for the most recent answer of you user -> a variable is enough.

if reply[0] == 'y':
    return 1
if reply[0] == 'n':
    return 0
else:
    return yes_or_no("Please Enter (y/n) ")

You have two if conditions after another: Python would check for == 'y' and then always check again for == 'n'. You need to use elif to declare an else-if condition, otherwise you waste resources or ran into unexpected behavior. Additionally, you are never using the return values. The while-loop just exits with a break statement, because it is a loop. Thus, your return statements are pointless.

回答3:

def yes_or_no(question):
    while True:
        answer = input(question + ' (y/n): ').lower().strip()
        if answer in ('y', 'yes', 'n', 'no'):
            return answer in ('y', 'yes')
        else:
            print('You must answer yes or no.')

yes_or_no('Do you like the plot?')

回答4:

you can't intialize an index of an array.

change reply[0] = 'n' to reply = 'n'

回答5:

First error - You never defined reply, so how do you index that string?

while True:
    reply[0] = 'n'  # What is reply??

Also break is outside the loop, which should be a SyntaxError.

Second error - You defined a loop, but never changed the value reply in the loop itself. Plus, yes_or_no() is called outside of the loop (but it never breaks the loop, only returns from the function).

You're having some misunderstanding about how functions work. They are separate code blocks, not intended to be nested within your other logic.

def yes_or_no(question):
    while True:
        reply = input(question + ' (y/n): ')).lower().strip()
        if reply.startswith('y'):
            break 

print("started")
yes_or_no('Do you like the plot')
print("done")

Or, probably a more readable version

def yes_or_no(question):
    return input(question + ' (y/n): ')).lower().strip()

print("started")
question = 'Do you like the plot?'
like_plot = yes_or_no(question).startswith('y')
while not like_plot:
    like_plot = yes_or_no(question).startswith('y')
print("done")

来源：https://stackoverflow.com/questions/47735267/while-loop-with-yes-no-input-python

标签

python

while-loop