click custom option prompt function

Question

I have noticed that prompt using click accepts inputs with trailing spaces

ftp_server = click.prompt("FTP Server")

Is there a way to use a custom return function like this to reject trailing spaces?

def custom_prompt(value):
    if value.strip():
        return True
    else:
        return False

ftp_server = click.prompt("FTP Server", custom_prompt)

I have already used this:

while not ftp_server.strip():
    ftp_server = click.prompt("FTP Server")

But I'm looking for a better way because I don't want to use a while loop each time I use prompt.

Answer 1

To reject invalid user input, you can use the value_proc parameter to click.prompt. A validator to reject input with trailing spaces could look like:

Prompt Validator

import click

def validate_no_trailing_space(value):
    if value != value.rstrip():
        raise click.UsageError("Trailing space is invalid!")
    return value

ftp_server = click.prompt("FTP Server",
                          value_proc=validate_no_trailing_space)

Trim Spaces

You might also consider a validator which trims leading and trailing spaces but reject spaces in the name:

def validate_no_internal_space(value):
    value = value.strip()
    if ' ' in value:
        raise click.UsageError("Spaces are not valid here!")
    return value