CODEWITHSUNDEEP
pythonstaticattributes
user366312
user366312

Reputation: 16908

How can I implement a static attribute in Python?

How can I implement a static property or method-pair in Python using a sharable and accessible static attribute?

class StaticClass:
    __static_attr: str

    @classmethod
    def set(cls, input__):
        cls.__static_class = input__

    @classmethod
    def get(cls):
        return cls.__static_attr


StaticClass.set("Hello!")
print(StaticClass.get())

Output:

C:\Users\pc\AppData\Local\Microsoft\WindowsApps\python3.7.exe C:/Users/pc/source/repos/main.py
Traceback (most recent call last):
  File "C:/Users/pc/source/repos/main.py", line 15, in <module>
    print(StaticClass.get())
  File "C:/Users/pc/source/repos/main.py", line 11, in get
    return cls.__static_attr
AttributeError: type object 'StaticClass' has no attribute '_StaticClass__static_attr'

Process finished with exit code 1

Edit: The above source code has a typo in set(). If that typo is fixed, the code runs perfectly.

However, in the case of my original source code, that attribute was a List[str]. In that case, the program only runs only if the attribute is initialized through a pair of square brackets [].

import os
from typing import List


class SearchFilesInTheDirectory:
    __file_list: List[str] = []

    @classmethod
    def do_indexing_of_files(cls, path, file_extension):
        for root, dirs, files in os.walk(path):
            for file in files:
                if file.endswith(file_extension):
                    cls.__file_list.append(os.path.join(root, file))

    @classmethod
    def get_files_list(cls):
        return cls.__file_list

    @classmethod
    def printf(cls):
        if cls.__file_list is not None:
            for file in cls.__file_list:
                print(file)
        else:
            print("directory is empty")

    @classmethod
    def write_to_file(cls, file_name):
        if cls.__file_list is not None:
            with open(file_name, 'w') as f:
                for f_name in cls.__file_list:
                    f.write("%s\t%s\n" % f_name)
        else:
            print("directory is empty")

Upvotes: 0

Views: 91

Answers (1)

Amitai Irron
Amitai Irron

Reputation: 2055

It would be a better idea is to initialize the class static variable, not just declare its type. This way you would be able to call get even before set, and have it return a default value:

class StaticClass:
    __static_attr = ""

    @classmethod
    def set(cls, input__):
        cls.__static_attr = input__

    @classmethod
    def get(cls):
        return cls.__static_attr


StaticClass.set("Hello!")
print(StaticClass.get())

Also, it seems like your original code had a typo, as a result of which set method was assigning to a variable other than the one you were declaring (__static_class instead of __static_attr). Because of that, and because the static variable was not initialized, your get method failed.

Upvotes: 1

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