如何检查列表中的所有项目是否都是字符串

Question

If I have a list in python, is there a function to tell me if all the items in the list are strings?

For Example: ["one", "two", 3] would return False , and ["one", "two", "three"] would return True .

Answer 1

Just use all() and check for types with isinstance() .

>>> l = ["one", "two", 3]
>>> all(isinstance(item, str) for item in l)
False
>>> l = ["one", "two", '3']
>>> all(isinstance(item, str) for item in l)
True

Answer 2

Answering @TekhenyGhemor's follow-up question: is there a way to check if no numerical strings are in a list. For example: ["one", "two", "3"] would return false

Yes. You can convert the string to a number and make sure that it raises an exception:

def isfloatstr(x):
    try: 
        float(x)
        return True
    except ValueError:
        return False

def valid_list(L):
    return all((isinstance(el, str) and not isfloatstr(el)) for el in L)

Checking:

>>> valid_list(["one", "two", "3"])
False

>>> valid_list(["one", "two", "3a"])
True

>>> valid_list(["one", "two", 0])
False

In [5]: valid_list(["one", "two", "three"]) Out[5]: True

Answer 3

Another way to accomplish this is using the map() function:

>>> all(map(lambda x: isinstance(x, str), ['one', 'two', 3]))
False
>>> all(map(lambda x: isinstance(x, str), ['one', 'two', 'three']))
True