Default values on empty user input

问题

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?

回答1:

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

How does it work?

If nothing was entered then raw_input returns empty string. Empty string in python is False bool("") -> False. Operator or returns first trufy 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.

回答2:

You can do it like this:

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

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

回答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"

回答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

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

回答5:

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"

回答6:

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

来源：https://stackoverflow.com/questions/22402548/default-values-on-empty-user-input

标签

python

user-input

default-value