在Python中将字符串转换为类（反之亦然）

Question

For a project that I am working on, I need to convert a string (which has ID numbers (ie ID_00000001...ID_00002032 or something like that)) into a class. By that I mean, there is already a class stored that has values like so:

class ID_00000001:
  name = 'Robert Johnson'
  age = 193
  facebook_url = 'facebook.com/Robert_johnson'
  etc.

I want to make it so that I can compare this profile to others. The way I was thinking of doing this was comparing values like (psudo):

current_profile_str = 'ID_00000001'
for i in range(len(all_IDs)):
  matches = []
  num = *converts number into 8 digit str*
  cycle_profile_str = 'ID_' + num
  *convert current_profile and cycle_profile to class*
  if (current_profile.age == cycle_profile.age):
      matches.append(cycle_profile_str)

So the question that I suppose I have in this context, is how would I be able to convert a string to a class?

Answer 1

You are using classes wrongly. You have one class, a facebook user. This could look like this:

class FacebookUser():
    def __init__(self, id, name, age, url):
        self.id = id
        self.name = name
        self.age = age
        self.url = url

You can then create instances for each user.

user1 = FacebookUser(1, 'John Doe', 27, 'facebook.com/john_doe')
user2 = FacebookUser(3, 'Jane Doe', 92, 'facebook.com/jane_doe')

print(user1.age == user2.age)

To represent a class as a string, you can add the __repr__ magic function to the class:

class FacebookUser():
    def __init__(self, id, name, age, url):
        self.id = id
        self.name = name
        self.age = age
        self.url = url

    def __repr__(self):
        return 'FacebookUser(id: {:08d}, name: {}, age: {})'.format(
             self.id,
             self.name,
             self.age,
        )

This will result in

>>> print(user1)
FacebookUser(id: 00000001, name: John Doe, age: 27)

For the other way around, you would implement an alternative constructor using a class method. These are methods belonging to a class, not to the instance. The first argument in these functions is the class cls , not the instance self :

class FacebookUser():
    def __init__(self, id, name, age, url):
        self.id = id
        self.name = name
        self.age = age
        self.url = url

    def __repr__(self):
        return 'FacebookUser(id: {:08d}, name: {}, age: {})'.format(
            self.id,
            self.name,
            self.age,
        )

    @classmethod
    def from_string(cls, string):
        '''
        Create a new instance from a string with format
        "id,name,age,url"
        '''
        _id, name, age, url = string.split(',')
        return cls(int(_id), name, int(age), url)

user1 = FacebookUser.from_string('1,John Doe,27,facebook.com/john_doe')

Answer 2

MaxNoe's answer is probably what you're looking for, but anyway...

If you really, actually want to somehow build up a class from a sequence of strings (For example, to have variables with their names extracted from the string itself, then you might want to look at metaclasses.

http://blog.ionelmc.ro/2015/02/09/understanding-python-metaclasses/