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:

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

回答8:

Functional way (one-liner)

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

回答9:

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10:

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11:

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 None
   print "Name is blank"
else: 
   print "Customer name : " + name

In the example above in case variable customer's value is None the it further gets casting while getting assigned to 'name'. The comparison in 'if' clause will always fail.

customer = "John" # even though its None still it will work properly.
name = customer
if name is None
   print "Name is blank"
else: 
   print "Customer name : " + str(name)

Above example will work properly. Such scenarios are very common when values are being fetched from URL, JSON or XML or even values need further type casting for any manipulation.

回答14:

If it is only about formatting strings, you can do the following:

from string import Formatter

class NoneAsEmptyFormatter(Formatter):
    def get_value(self, key, args, kwargs):
        v = super().get_value(key, args, kwargs)
        return '' if v is None else v

fmt = NoneAsEmptyFormatter()
s = fmt.format('{}{}', a, b)

回答15:

Use short circuit evaluation:

s = a or '' + b or ''

Since + is not a very good operation on strings, better use format strings:

s = "%s%s" % (a or '', b or '')

回答16:

Use F string if you are using python v3.7

xstr = F"{s}"

来源：https://stackoverflow.com/questions/1034573/python-most-idiomatic-way-to-convert-none-to-empty-string

标签

string

python

idioms