How to let the user select an input from a finite list?

Question

Is it possible to ask for selection between multiple choices in Python, without an if loop?

Example:

print "Do you want to enter the door"
raw_input ("Yes or not")

And the user can only choose between the selections.

Murdock

if is not a loop. Why don't you want to use if? – Overleap

the idea is that if you don't write "Yes" or "No", nothing will appear, the program will just wait from you to write one of the two and not proceeding. – Murdock

You are going to need a loop to do that – Lights

You can't really avoid a loop and an if for this case (I mean it's certainly possible without but why someone would do that ?). If the problem is that you don't want a lot of loops and if in your code just write a function. – Aindrea

Answer 1

If you need to do this on a regular basis, there is a convenient library for this purpose that may help you achieve better user experience easily : inquirer

Disclaimer : As far as i know, it won't work on Windows without some hacks.

You can install inquirer with pip :

pip install inquirer

Example 1 : Multiple choices

One of inquirer's feature is to let users select from a list with the keyboard arrows keys, not requiring them to write their answers. This way you can achieve better UX for your console application.

Here is an example taken from the documentation :

import inquirer
questions = [
  inquirer.List('size',
                message="What size do you need?",
                choices=['Jumbo', 'Large', 'Standard', 'Medium', 'Small', 'Micro'],
            ),
]
answers = inquirer.prompt(questions)
print answers["size"]

Example 2 : Yes/No questions :

For "Yes/No" questions such as yours, you can even use inquirer's Confirm :

import inquirer
confirm = {
    inquirer.Confirm('confirmed',
                     message="Do you want to enter the door ?" ,
                     default=True),
}
confirmation = inquirer.prompt(confirm)
print confirmation["confirmed"]

Others useful links :

Inquirer's Github repo

Kooima

Oh, that's exactly what I meant. No way to make it work on windows? – Murdock

It's probably possible, but i havent managed to make it work on windows so far. I didn't dig too much as i didn't needed it to work on windows when i used it... – Kooima

For Windows users, try PyInquirer which works great. And here is the link to their documentation: github.com/CITGuru/PyInquirer – Frilling

github.com/wong2/pick also supports Windows, with a simple and small API – Chryselephantine

Answer 2

This is a bit of an overkill for only selecting yes or no but it is a generic solution also working for more then two options. And it is protected for non existing options and will force the user to give a new valid input. This without any imports.

First a function which handles all functionality:

def selectFromDict(options, name):
    index = 0
    indexValidList = []
    print('Select a ' + name + ':')
    for optionName in options:
        index = index + 1
        indexValidList.extend([options[optionName]])
        print(str(index) + ') ' + optionName)
    inputValid = False
    while not inputValid:
        inputRaw = input(name + ': ')
        inputNo = int(inputRaw) - 1
        if inputNo > -1 and inputNo < len(indexValidList):
            selected = indexValidList[inputNo]
            print('Selected ' +  name + ': ' + selected)
            inputValid = True
            break
        else:
            print('Please select a valid ' + name + ' number')
    return selected

Then a dict with all options

options = {}
#     [USER OPTION] = PROGRAM RESULT
options['Yes'] = 'yes'
options['No'] = 'no'

And then call the function with the options

# Let user select a month
option = selectFromDict(options, 'option')

The result is:

> Select a option:
> 1) Yes
> 2) No
> option: 3
> Please select a valid option number
> option: 1
> Selected option: yes

As said this is saleable to for instance all months of the year re-using the function above:

months = {}
months['January'] = 'jan'
months['February'] = 'feb'
months['March'] = 'mar'
months['April'] = 'apr'
months['May'] = 'may'
months['June'] = 'jun'
months['July'] = 'jul'
months['August'] = 'aug'
months['September'] = 'sep'
months['October'] = 'oct'
months['November'] = 'nov'
months['December'] = 'dec'

# Let user select a month
month = selectFromDict(months, 'Month')

Example result:

> Select a Month:
> 1) January
> 2) February
> 3) March
> 4) April
> 5) May
> 6) June
> 7) July
> 8) August
> 9) September
> 10) October
> 11) November
> 12) December
> Month: 5
> Selected Month: may

Cadent

Answer 3

One possible way to achieve what you appear to require is with a while loop.

print "Do you want to enter the door"
response = None
while response not in {"yes", "no"}:
    response = raw_input("Please enter yes or no: ")
# Now response is either "yes" or "no"

Woodcock

Just curious, is using a set for the options {"yes", "no"} better / faster than using a list? – Lights

In the two-element case it will make hardly any difference, but a set becomes much faster as the number of elements goes up. The reason for this is the underlying implementation of the __contains__ method, which for a list iterates over each element until it finds a match or exhausts all the elements. For a set, hashing techniques are used to give almost constant execution time regardless of the number of elements. – Woodcock

Answer 4

For an OS agnostic solutions using prompt-toolkit 2 or 3, use questionary

https://github.com/tmbo/questionary

Cruiserweight

Answer 5

For those in Python 3, and that want a non case sensitive option:

def ask_user():
    print("Do you want to save?")
    response = ''
    while response not in {"yes", "no"}:
        response = input("Please enter yes or no: ").lower()
    return response == "yes"

---

And, if I understand Assignment Expressions (PEP 572) correctly, in Python 3.8 you will be able to do this:

def ask_user():
    while r:= input("Do you want to save? (Enter yes/no)").lower() not in {"yes", "no"}:
        pass
    return r == "yes"

Appurtenance

While the walrus formulation is superficially "neat," readability is also a factor, and the use of a pass loop body will, I suspect, increase cognitive load for most readers. A while loop with a real body and the right initial condition seemed the more natural formulation to me. There's always room for differences of opinion in programming. – Woodcock

In the first option, it's simpler to do response = input(...).lower(). Then you can also do response = None for a more solid sentinel value. – Bilection

@wjandrea, I agree with the first part and modified accoridingly, but I am not sure about the response=None making it a more solid sentinel value, feel free to edit directly. – Appurtenance

@Appurtenance Nah, that's fine, on second thought, having a different type as a sentinel might have drawbacks. – Bilection

Answer 6

If you use Windows and you need the immediate input with one character, the this should work:

import os

inp = "yn"

if os.system("choice /c:%s /n /m \"Yes or No (Y/N)\"" % inp) - 2:
    # if pressed Y
    print("Yes")
else:
    # if pressed N
    print("No")

P. S.: This code works on Python 3

Austinaustina