Python 3.x What's the best way to do this code?

Question

I am writing a code where the user inputs as many numbers as they want until they input Stop. Each input gets added to a list. I want the input to be integer so the inputs are able to be sorted correctly but then when 'Stop' is inputted an error message will be created. But if I make the input string then the numbers will be sorted incorrectly.

Here is the code:

Num_List = list()
Numbers = input('Enter a number: ')
Num_List.append(Numbers)
Num_B = False
while Num_B == False:
    Numbers = input('Enter a number: ')
    Num_List.append(Numbers)
    if Numbers == 'Stop':
        Num_List.remove('Stop')
        Num_List = [i for i in Num_List if i is not '']      
        Num_List.sort(reverse=False)
        sorted(Num_List)
        print(Num_List)
        Num_B = True

_"when 'Stop' is inputted an error message will be created."_ What is the error message? — Kevin, Dec 01 '15 at 13:43
@Cyrbil, agreed, but only if OP is using 2.7 or lower. I think he may not actually be using 3.X, but is not aware of that fact. — Kevin, Dec 01 '15 at 13:50
@Jaxt65, add your error traceback, also `sorted(Num_List)` is doing nothing in your code — Padraic Cunningham, Dec 01 '15 at 14:09
@jaxt65,the traceback from any error is as if not more important than the code, there are different reasons why your code would error which adding the traceback would narrow down to one — Padraic Cunningham, Dec 01 '15 at 19:27

Cyrbil · Answer 1 · 2015-12-01T15:18:15.287

I suspect that you are using python <2.8, so input() behave differently and execute what is given instead of returning it as string (like eval(input())). When given an int, no problems occurs but when given a "Stop", python does not know what to do with it (unless your code have a variable named "Stop" ...).

Here is a simple rework of your code for python2:

# little trick to use input with python2 or python3 !
# source: http://stackoverflow.com/a/7321970/956660
try: input = raw_input
except NameError: pass

# variables naming is prefered in snake_case
num_list = []
curr_num = '' # only use one variable for input
while curr_num.lower() != 'stop': # lower allows to be case insensitive
    # raw_input prevent the "bug"
    curr_num = input('Enter a number or "stop": ')

    # conversion to int raise an error on invalid string, so we ignore errors
    try: num_list.append(int(curr_num))
    except ValueError: pass

# we print and sorted only when everything have been inputted
print('Numbers: %s' % num_list)
print('Sorted: %s' % sorted(num_list))

Edit: Refactor code to be python 2 & 3 compatible. So you can use input() the same way anywhere ;)

After I modified my code in update 2, I saw your raw_input/input trick. Credit go to your source, because that is where I learned it from — Hai Vu, Dec 01 '15 at 14:30

Hai Vu · Accepted Answer · 2015-12-01T20:26:24.100

0

Here is my approach: In an infinite loop, get a user's input. If it is 'Quit' then break out of the loop. Otherwise, convert to integer and append to the list of numbers. The code:

numbers = list()
while True:
    token = input('Number: ')
    if token == 'Quit':
        break
    numbers.append(int(token))

print('List is:', numbers)

Update

Judging by the original poster's ignoring empty strings, I guess some of the imput are empty strings, which causes ValueError. With that guess, I modified my code to take in accounts of those tokens that are not converted to numbers successfully.

numbers = list()
while True:
    token = input('Number: ')
    if token == 'Stop':
        break
    try:
        numbers.append(int(token))
    except ValueError:
        print('Invalid token, ignore: {!r}'.format(token))

print('List is:', numbers)

Update 2:

I have modifying my code yet again. This time, the code runs fine in both Python 2 and 3 interpreters.

from __future__ import print_function

# Level the difference between Python 2 and 3
try:
    raw_input
except NameError:
    raw_input = input

numbers = list()
while True:
    try:
        token = raw_input('Number: ')
        numbers.append(int(token))
    except ValueError:
        if token == 'Stop':
            break
        print('Invalid token, ignore: {!r}'.format(token))

print('List is:', numbers)

Update 3

Output for update 2 from Python 3 run:

Number: 7
Number: 87
Number: 120
Number: 
Invalid token, ignore: ''
Number: foo
Invalid token, ignore: 'foo'
Number: bar
Invalid token, ignore: 'bar'
Number: Stop
List is: [7, 87, 120]

Output from Python 2 run is the same.

edited Dec 01 '15 at 20:26

answered Dec 01 '15 at 13:55

Hai Vu

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How does this address the error? Inputting `Stop` in your code is also going to error if the OP is using python2 which based on the problem description is most likely what is happening? – Padraic Cunningham Dec 01 '15 at 13:58
@PadraicCunningham I ran the OP's code and did not see any error. I am still waiting for the OP to update with any specific error. My post do address the OP concern: converting the tokens to integers. – Hai Vu Dec 01 '15 at 14:05
The OP's own code breaks when Stop is entered which is what would happen using python2 as there would be a `NameError` using input. – Padraic Cunningham Dec 01 '15 at 14:09
The OP specifically stated Python 3. Yes, I am well aware of the different between `input` and `raw_input` in Python 2.x. – Hai Vu Dec 01 '15 at 14:12
It works except for a few problems: 1. Typing Stop does nothing, anything other than Stop prints the list 2. It prints the first number fine but all the others get repeated twice. – Dec 01 '15 at 18:13
I tested my solution. Perhaps if you care showing me your input sequence so I can test (and fix) – Hai Vu Dec 01 '15 at 18:19
Typing in numbers work and adds it to a list. Words do not get added. '' causes a value error. Inputting 7, 87, 120 outputs [7, 87, 87, 120, 120]. It only stops when inputting something that isn't Stop. – Dec 01 '15 at 19:24
Are you sure you are running my update 2 version? I added update 3 to show the output and it looks alright to me. – Hai Vu Dec 01 '15 at 20:27
Yes, the only difference is the variabee names, raw_input is input and everything above nukbers = list() (I do not know if I need everything above numbers = list() or not, I am using Pythin 3.x) – Dec 01 '15 at 21:33

Ryan · Answer 3 · 2015-12-01T14:10:04.963

0

You can do it like this:

Num_List = list()
Numbers = input('Enter a number:')
while Numbers != 'Stop':
    Num_List.append(int(Numbers))
    Numbers = input('Enter a number:')

Num_List = [i for i in Num_List if i is not '']      
Num_List.sort(reverse=False)
sorted(Num_List)
print(Num_List)

edited Dec 01 '15 at 14:10

answered Dec 01 '15 at 13:56

Ryan

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Python 3.x What's the best way to do this code?

3 Answers3

Update

Update 2:

Update 3