如何检查对象是否是一个字符串列表?我只能检查对象是否是字符串,例如:
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)
所需的输出:
It's a list of strings
It's not a list of strings or a single string
It's a single string
像这样的事情,我相信?你可以做一些检查,看它是否是一个字符串。
>>> 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
为什么检查basestring
而不是str
?
您应该检查basestring
而不是str
因为它是从两个str
和unicode
类型继承一个共同的类。仅检查str
省去了unicode
类型。
按照Steven Rumbalski's建议,如果你需要特别检查的字符串列表,你可以做。
>>> 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 - 按abarnert's建议,你也可以检查一个list
而不是not isinstance(lst, basestring)
,代码会得到改写为。
>>> 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
移动从一个套了,我们可以使用。
>>> def is_list_of_strings(lst):
if lst and isinstance(lst, list):
return all(isinstance(elem, basestring) for elem in lst)
else:
return False
为了测试列表中的所有项目都是字符串,使用all
内置和发电机:
if all(isinstance(s, str) for s in lis):
不过,请注意,如果你的列表是空的,这仍然会返回True
因为这在技术上是0字符串列表。不过,既然你要考虑[]
为False
,你需要这样做:
if lis and all(isinstance(s, str) for s in lis):
所以,你的函数应该是这样的:
def checktype(obj):
# This if statement makes sure input is a list that is not empty
if obj and isinstance(obj, list):
return all(isinstance(s, str) for s in obj)
else:
return False
此功能仅返回True
如果输入的是一个非空列表,即完全由字符串。别的(如[]
,['a', 1]
,('a', 'b')
等)将使其返回False
。
此外,以这种方式使用all
有一个额外的好处,因为它停止检查它找到的第一个项目,返回False
(不是字符串)。这使您可以非常大名单相当有效地工作。
我读过的答案给出一个非列表不是一个字符串时为止提高exepctions ...并没有任何可迭代。这个问题被处理了:
In Python, how do I determine if an object is iterable?
以鸭打字的方法:
def categorize(x):
result = "not a string or list of strings"
if isinstance(x, basestring):
return "It's a single string"
try:
if all(isinstance(y, basestring) for y in x):
return "It's a list of strings"
except TypeError:
pass
return "It's not a list of strings or a single string"
data = [ 5, "xyzzy", list("xyzzy"), ['1', '23', 456]]
for x in data:
print x, categorize(x)
输出:
5 It's not a list of strings or a single string
xyzzy It's a single string
['x', 'y', 'z', 'z', 'y'] It's a list of strings
['1', '23', 456] It's not a list of strings or a single string
这个答案就是Python 3。举例来说,如果变量名是pins
:
if not (pins and isinstance(pins, list) and all(isinstance(pin, str) for pin in pins)):
raise TypeError('pins must be a list of one or more strings.')
它检查三件事情:
如果你还需要检查弦的独特性,包括第四检查:
and (len(tokens) == len(set(tokens)))