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 '')
