Python: most idiomatic way to convert None to empty string?

问题:

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)

回答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)

回答2:

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

回答3:

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) # -> ''

回答4:

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.

回答5:

return s or '' will work just fine for your stated problem!

回答6:

def xstr(s):    return s or ""

回答7:

Functional way (one-liner)

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

回答8:

def xstr(s):     return {None:''}.get(s, s)

回答9:

Variation on the above if you need to be compatible with Python 2.4

xstr = lambda s: s is not None and s or ''

回答10:

I use max function:

max(None, '')  #Returns blank max("Hello",'') #Returns Hello

Works like a charm ;) Just put your string in the first parameter of the function.

回答11:

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 '')

回答12:

def xstr(s):     return s if s else ''  s = "%s%s" % (xstr(a), xstr(b))

回答13:

We can always avoid type casting in scenarios explained below.

customer = "John" name = str(customer) if name is