在 f-string 中避免 None

Question

If I have an f-string where one of the parameters may be None , is there a way to automatically omit it from the string?

f'{first_name} {prefix} {last_name}'

If prefix is None then this string will render as Arnold None Weber .

I tried f'{first_name} {prefix or ''} {last_name}' but that's a syntax error.

Answer 1

I tried f'{first_name} {prefix or ''} {last_name}' but that's a syntax error.

The only reason it's a syntax error is that you tried to put single quotes inside single quotes. All of the usual ways of fixing it will work:

f'{first_name} {prefix or ""} {last_name}'
f"{first_name} {prefix or ''} {last_name}"
f"""{first_name} {prefix or ''} {last_name}"""

However, notice that this doesn't quite do what you want. You won't get Arnold Weber , but Arnold Weber , because the spaces on either end aren't conditional. You could do something like this:

f'{first_name} {prefix+" " if prefix else ""}{last_name}'
f'{first_name} {prefix or ""}{" " if prefix else ""}{last_name}'

… but at that point, I don't think you're getting the conciseness and readability benefits of f-strings anymore. Maybe consider something different, like:

' '.join(part for part in (first_name, prefix, last_name) if part)
' '.join(filter(None, (first_name, prefix, last_name)))

Not that this is shorter —but the logic is a lot clearer.

Answer 2

Of course it's a syntax error; you broke your string.

f'{first_name} {prefix or ""} {last_name}'