如何为对象列表返回int类型表示

Question

When outputting a list of objects how can you return an int type representation for the objects?

I've tried this:

class Passport(object):
    def __init__(self, my_id):
        self.id = my_id

    def __repr__(self):
        return int(self.id)



list_of_objects = [
Passport(19181),
Passport(29191),
Passport(39191)
]

if id in list_of_objects:
    print("true")

Where list_of_objects is a list of Passport instances. But this gives an error __repr__ returned non-string (type int) .

I could solve this problem using a string for both, but I'm wondering if type int is possible?

Answer 1

__repr__ is required to return a string representation of the object. Returning a different type is not a valid implementation of __repr__ .

If you want a way to return some number, then add a custom method that does that.

Btw., note that implementing __repr__ is not a way to make id in list_of_objects work. For that to work, you should implement __hash__ and __eq__ . But at that point, you should really think about if you want 5 == Passport(5) to be true; probably not. So you should change the way your check works by explicitely looking at the id property instead.

Instead of if id in list_of_objects , you could do the following:

if any(lambda x: x.id == id, list_of_objects):
    print('true')

Answer 2

You could check a parallel list of the object ids instead.

if any(id == pp.id for pp in list_of_objects):
    print("true")

Answer 3

__repr__ must return a str as you have seen.

The proper way to do what you are asking is:

list_of_object_ids = [p.id for p in (Passport(19181), Passport(29191), Passport(39191))]
if id in list_of_objects:
    print("true")

Answer 4

class Passport(object):
    def __init__(self, my_id):
        # It is recommended to call int here also in order to prevent
        # construction of invalid objects.
        self.id = int(my_id)

    def __int__(self):
        return int(self.id)

list_of_objects = [
Passport(19181),
Passport(29191),
Passport(39191)
]

list_of_ints = [int(passport) for passport in list_of_objects]

if id in list_of_ints:
    print("true")