Create a Tempfile with lifespan as the object

Question

I have a project where I need to create temp files.

I have a class that accepts a file path. and as needed it reads the data from the file. However, sometimes I have the data and I want to create the same object so I use tempfile. But I want the file to be deleted as the object garbage-collected.

This is my implementation which is wrong.

from pickle import load
import tempfile


class A:
    def __init__(self, file_path):
        self.file_path = file_path

    @property
    def data(self):
        with open(self.file_path, "rb") as f2r:
            return load(f2r)

    @classmethod
    def from_data(cls, data):
        with tempfile.NamedTemporaryFile() as tmp:
            tmp.write(data)
            return cls(tmp.name)

The from_data method creates the temp file and returns an object but the file will be deleted as soon as from_data returns the object. But I want the file to live until the object itself is garbage-collected.

Wouldn't it be more robust to turn A into a context manager, and close the tempfile as part of the exit from your context manager? — Nick ODell
– Nick ODell, Commented Sep 9, 2023 at 0:54
I see what you say. But this example is a pseudo example of a more complex project and the design cannot be changed like that. — niaei
– niaei, Commented Sep 9, 2023 at 1:01
What if you overrode the finalizer, __del__ so that it closes the tempfile when it is garbage collected? See also stackoverflow.com/questions/1481488/… — Nick ODell
– Nick ODell, Commented Sep 9, 2023 at 1:13
That's what I thought but I wanted to ask if there is a more elegant way to do so. But If you suggest so I'll implement it. — niaei
– niaei, Commented Sep 9, 2023 at 1:16

niaei · Accepted Answer · 2023-09-09 01:25:01Z

0

As @Nick ODell suggested I am going to use __del__ method to delete the file on garbage-collection.

So the code would look like:

from pathlib import Path
from pickle import load
import tempfile


class A:
    def __init__(self, file_path):
        self.file_path = file_path
        self.is_temp = False

    def __del__(self):
        if self.is_temp:
            Path(self.file_path).unlink()

    @property
    def data(self):
        with open(self.file_path, "rb") as f2r:
            return load(f2r)

    @classmethod
    def from_data(cls, data):
        with tempfile.NamedTemporaryFile(delete=False) as tmp:
            tmp.write(data)
            a = cls(tmp.name)
            a.is_temp = True
            return a

answered Sep 9, 2023 at 1:25

niaei

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