Pass class type as argument to class constructor

April 2, 2022

Say I have a Directory class which accepts a list of other sub-directories as an argument:

class File:
    pass

class Directory:
    def __init__(self, directories: List[Directory], files: List[File]):
                                         ^^^^^^^^^
        self.directories = directories
        self.files = files

I am getting an error saying "Directory" is not defined. This code works just fine if I don’t pass the types, but how do you handle this use-case in python?

>Solution :

What you need is a recursive typing definition. This can be achieved in Python by providing a string with the name of the type, rather than the type itself.

class File:
   pass

class Directory:
   def __init__(self, directories: List['Directory'], files: List[File]):
      self.directories = directories
      self.files = files