How to check if the Enter key was pressed while using the Walrus operator in Python?

Question

I'm trying to get input from a user using the Walrus operator :=, but if the user will only type in the Enter key as input, than the python script will terminate. How can I catch this error and make sure that the user hasn't only pressed the Enter key?

There is this answer but it does not work using the walrus operator.

This code without the walrus operator will successfully check that not only the Enter key was pressed:

while True:
    answer = input("Please enter something: ")
    if answer == "":
        print("Invalid! Enter key was pressed.")
        continue
    else:
        print("Enter wasn't pressed!")
        # do something

If the user only presses Enter, than the whole script will terminate.

while answer := input("Please enter something: "):
    # if user pressed only `Enter` script will terminate. following will never run
    if answer == "":
        print("enter was pressed")
    else:
        print("Enter wasn't pressed!")
        # do something

Obviously walrus operator is not suitable for this use case. It doesn't make the code shorter or more readable either. Your original (working) solution is superior. — Selcuk, Jul 16 '20 at 00:56
`Enter` only will create a zero length string, which will evaluate to `False` for the while loop, therefore the block will exit without executing. — RufusVS, Jul 16 '20 at 02:12

bigbounty · Answer 1 · 2020-07-16T00:57:20.823

What's happening in the code?

Part 1:

This happens because this statement answer := input("Please enter something: ") takes the input value and assigns to the variable answer. If you press Enter then the value for answer is empty string.

Part 2:
while loop evaluates the value. As the value is an empty string and empty string evaulates to false, the loop exits

We can't do this using walrus operator because the control never goes inside the loop and moreover you want to check the value of the entered string

wjandrea · Accepted Answer · 2020-07-16T02:03:22.737

You put the assignment expression in the wrong spot. Your original loop is infinite, but your second loop uses answer as the break condition.

while True:
    if not (answer := input("Type something: ")):
        print("You didn't type anything before pressing Enter!")
        continue
    print("You typed:", answer)

As well, since we're using continue, the else clause is not needed.

In action:

Type something: hello!
You typed: hello!
Type something:
You didn't type anything before pressing Enter!
Type something: hi!
You typed: hi!

However, there's no real advantage to using the walrus operator here, so I would avoid it.

while True:
    answer = input("Type something: ")
    if not answer:
        print("You didn't type anything before pressing Enter!")
        continue
    print("You typed:", answer)

score -1 · Answer 3 · answered Jul 16 '20 at 00:55

-1

You can write the following code:

while (answer := input("Please enter something: ")) != 0:
    # if user pressed only `Enter` script will terminate. following will never run
    if answer == "":
        print("enter was pressed")
    else:
        print("Enter wasn't pressed!")
        # do something

This means that != 0 will always be satisfied.

answered Jul 16 '20 at 00:55

KetZoomer

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This is a terrible use of the walrus operator. It would be so much clearer to do `while True: answer = input()`, like OP had in the first place. – wjandrea Jul 16 '20 at 01:53

How to check if the Enter key was pressed while using the Walrus operator in Python?

3 Answers3