Python：检查对象是否是字符串列表

Question

如何检查对象是否为字符串列表？我只能检查对象是否为字符串：

def checktype(obj):
  if isinstance(obj,str):
    print "It's a string"

obj1 = ['foo','bar','bar','black','sheet']
obj2 = [1,2,3,4,5,'bar']
obj3 = 'bar'

for i in [obj1,obj2,obj3]:
  checktype(i)

期望输出：

It's a list of strings
It's not a list of strings or a single string
It's a single string

Answer 1

我想是这样吧？你可以检查一下是不是一根线。

>>> def checktype(obj):
        return bool(obj) and all(isinstance(elem, basestring) for elem in obj)

>>> obj1 = ['foo','bar','bar','black','sheet']
>>> obj2 = [1,2,3,4,5,'bar']
>>> obj3 = 'bar'
>>> for i in [obj1, obj2, obj3] :
        print checktype(i)


True
False
True

为什么要检查basestring而不是str？

您应该检查basestring，而不是str，因为它是一个公共类，str和unicode类型都从中继承。只检查str会遗漏unicode类型。

根据Steven Rumbalski's建议，如果需要特别检查字符串列表，可以这样做。

>>> def is_list_of_strings(lst):
        return bool(lst) and not isinstance(lst, basestring) and all(isinstance(elem, basestring) for elem in lst)
        # You could break it down into `if-else` constructs to make it clearer to read.

>>> for i in [obj1, obj2, obj3] :
        print is_list_of_strings(i)


True
False
False

编辑-根据abarnert's建议，您还可以检查list而不是not isinstance(lst, basestring)，代码将被重写为。

>>> def is_list_of_strings(lst):
        return bool(lst) and isinstance(lst, list) and all(isinstance(elem, basestring) for elem in lst)
        # You could break it down into `if-else` constructs to make it clearer to read.

>>> for i in [obj1, obj2, obj3] :
        print is_list_of_strings(i)


True
False
False

我们可以不用一句台词。

>>> def is_list_of_strings(lst):
        if lst and isinstance(lst, list):
            return all(isinstance(elem, basestring) for elem in lst)
        else:
            return False