CODEWITHSUNDEEP
pythonpython-3.xtimeout
Kamyar
Kamyar

Reputation: 2694

Variable with timeout in Python

I need to declare a variable with timeout in Python! Actually I need something like REDIS timeout when we try to read a key after timeout, we get null (None). I know the variable can be deleted and after that, reading the variable would raise errors, but returning None is enough for me. Is there any ready library/package to fulfill this requirement or help me do this without boilerplate code?

Upvotes: 2

Views: 1790

Answers (2)

Harish Rajagopal
Harish Rajagopal

Reputation: 1242

Here is a custom class for a variable with a timeout, without the need to install a third-party package:

import time


class TimeoutVar:
    """Variable whose values time out."""

    def __init__(self, value, timeout):
        """Store the timeout and value."""
        self._value = value
        self._last_set = time.time()
        self.timeout = timeout

    @property
    def value(self):
        """Get the value if the value hasn't timed out."""
        if time.time() - self._last_set < self.timeout:
            return self._value

    @value.setter
    def value(self, value, timeout=None):
        """Set the value while resetting the timer."""
        self._value = value
        self._last_set = time.time()
        if timeout is not None:
            self.timeout = timeout

You can save this in a file, say timeout_var.py, then import the class in your code. This can be used as follows:

import time
from timeout_var import TimeoutVar

var = TimeoutVar(value=3, timeout=5)
print(var.value)
time.sleep(5)
print(var.value)

var.value = 7
print(var.value)
time.sleep(5)
print(var.value)

The output is:

3
None
7
None

When you assign the value attribute a new value, the internal timer is also reset.

Upvotes: 3

Gabio
Gabio

Reputation: 9504

Try ExpiringDict. It allows you to define a dictionary with key's expiration.

First, install the package:

pip install expiringdict

Here is an example for basic usage:

import time
from expiringdict import ExpiringDict
vars_with_expiry = ExpiringDict(max_age_seconds=1, max_len=100)
vars_with_expiry["my_var"] = "hello"
print(vars_with_expiry.get("my_var")) # hello
time.sleep(2)
print(vars_with_expiry.get("my_var")) # None

vars_with_expiry is a dictionary with expiry timeout of 1 second and max length of 100 keys (ExpiringDict requires a predefined size param during the initilization).

In the above example you can see how the key my_var is deleted and is not available after the sleep.

Upvotes: 2

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