How to define default value if empty user input in Python?

Question

Here I have to set the default value if the user will enter the value from the keyboard. Here is the code that user can enter value:

input = int(raw_input("Enter the inputs : "))

Here the value will be assigned to a variable input after entering the value and hitting Enter. Is there any method that if we don't enter the value and directly hit the Enter key, the variable will be directly assigned to a default value, say as input = 0.025?

Answer 1

Python 3:

inp = int(input("Enter the inputs : ") or "42")

Python 2:

inp = int(raw_input("Enter the inputs : ") or "42")

How does it work?

If nothing was entered then input/raw_input returns empty string. Empty string in Python is False, bool("") -> False. Operator or returns first truthy value, which in this case is "42".

This is not sophisticated input validation, because user can enter anything, e.g. ten space symbols, which then would be True.

Answer 2

You can do it like this:

>>> try:
        input= int(raw_input("Enter the inputs : "))
    except ValueError:
        input = 0

Enter the inputs : 
>>> input
0
>>> 

Answer 3

One way is:

default = 0.025
input = raw_input("Enter the inputs : ")
if not input:
   input = default

Another way can be:

input = raw_input("Number: ") or 0.025

Same applies for Python 3, but using input():

ip = input("Ip Address: ") or "127.0.0.1"

Answer 4

You can also use click library for that, which provides lots of useful functionality for command-line interfaces:

import click

number = click.prompt("Enter the number", type=float, default=0.025)
print(number)

Examples of input:

Enter the number [0.025]: 
 3  # Entered some number
3.0

or

Enter the number [0.025]: 
    # Pressed enter wihout any input
0.025

Answer 5

You could first input a string, then check for zero length and valid number:

input_str = raw_input("Ender the number:")

if len(input_str) == 0:
    input_number = DEFAULT
else:
    try:
        input_number = int(input_str)
    except ValueError:
        # handle input error or assign default for invalid input

Answer 6

Most of the above answers are correct but for Python 3.7, here is what you can do to set the default value.

user_input = input("is this ok ? - [default:yes] \n")
if len(user_input) == 0 :
    user_input = "yes"

Answer 7

Here is an example to validate user input to be a number and also set default value if he enters nothing.

while True:
    luckyNo = input("Enter your lucky number - [default:108]: ").strip()
    if luckyNo.isdigit(): # check if user entered a number
        luckyNo = int(luckyNo) # convert entered number to integer
        break
    else:  
        if not luckyNo: # user entered nothing
            print("You entered nothing. Using default value...")
            luckyNo = 108 # set default value
            break
        else: # user entered something other than a number
            print("Wrong input!. Try again.")

print("Your lucky number is " + str(luckyNo))