### Question :

What is the most idiomatic way to do the following?

```
def xstr(s):
if s is None:
return ''
else:
return s
s = xstr(a) + xstr(b)
```

**update:** I’m incorporating Tryptich’s suggestion to use str(s), which makes this routine work for other types besides strings. I’m awfully impressed by Vinay Sajip’s lambda suggestion, but I want to keep my code relatively simple.

```
def xstr(s):
if s is None:
return ''
else:
return str(s)
```

##
Answer #1:

If you actually want your function to behave like the `str()`

built-in, but return an empty string when the argument is None, do this:

```
def xstr(s):
if s is None:
return ''
return str(s)
```

##
Answer #2:

```
def xstr(s):
return '' if s is None else str(s)
```

##
Answer #3:

Probably the shortest would be

`str(s or '')`

Because None is False, and “x or y” returns y if x is false. See Boolean Operators for a detailed explanation. It’s short, but not very explicit.

##
Answer #4:

If you know that the value will always either be a string or None:

```
xstr = lambda s: s or ""
print xstr("a") + xstr("b") # -> 'ab'
print xstr("a") + xstr(None) # -> 'a'
print xstr(None) + xstr("b") # -> 'b'
print xstr(None) + xstr(None) # -> ''
```

##
Answer #5:

`return s or ''`

will work just fine for your stated problem!

##
Answer #6:

```
def xstr(s):
return s or ""
```

##
Answer #7:

Functional way (one-liner)

```
xstr = lambda s: '' if s is None else s
```

##
Answer #8:

A neat one-liner to do this building on some of the other answers:

```
s = (lambda v: v or '')(a) + (lambda v: v or '')(b)
```

or even just:

```
s = (a or '') + (b or '')
```