Python lambda returning None instead of empty string

Question

I have the following lambda function:

f = lambda x: x == None and '' or x

It should return an empty string if it receives None as the argument, or the argument if it's not None.

For example:

>>> f(4)
4
>>> f(None)
>>>

If I call f(None) instead of getting an empty string I get None. I printed the type of what the function returned and I got NoneType. I was expecting string.

type('') returns string, so I'd like to know why the lambda doesn't return an empty string when I pass None as an argument.

I'm fairly new to lambdas so I might have misunderstood some things about how they work.

Answer 1

use the if else construct

f = lambda x:'' if x is None else x

Answer 2

The problem in your case that '' is considered as boolean False. bool('') == False. You can use

f =lambda x:x if x is not None else ''