Passing Python class by reference with type initialized error

What will you learn?

In this post, you will delve into passing a generic Python class by reference and effectively handling the AttributeError: ‘typing.TypeVar’ object has no attribute issue.

Introduction to the Problem and Solution

Encountering an AttributeError related to typing.TypeVar when passing a generic Python class by reference with type initialized can be frustrating. To conquer this hurdle, it’s essential to grasp how Python manages types and references in dealing with classes.

To tackle this issue, leveraging TypeVar from the typing module in Python proves to be the key. By accurately defining types for referencing classes, you can sidestep running into the aforementioned AttributeError.


# Importing TypeVar from typing module
from typing import TypeVar

# Define a sample generic class using TypeVar
T = TypeVar('T', int, float, str)

class GenericClass:
    def __init__(self, value: T):
        self.value = value

# Creating an instance of GenericClass with integer type
obj = GenericClass(10)

# Copyright PHD



  • Import TypeVar from the typing module.
  • Define a custom generic class named GenericClass that accepts a parameter of type T, which can be an integer, float, or string.
  • Utilize TypeVar to ensure your generic class supports various data types without encountering attribute errors during initialization or usage.
    How can I fix the ‘AttributeError: ‘typing.TypeVar’ object has no attribute’ issue?

    Ensure correct import of TypeVar from the typing module and appropriate definition of custom class parameters.

    Can I specify multiple data types for my generic class in Python?

    Yes, you can define multiple data types using TypeVar within your custom classes for handling different input types flexibly.

    Is it necessary to always initialize variables explicitly when using generics in Python?

    Explicit initializations are recommended when working with generics to prevent unexpected errors during runtime execution.

    Will defining complex nested structures impact performance when using generics?

    While complex nested structures may slightly affect performance due to additional type checking overheads, they enhance code readability and maintainability in the long run.

    How does Python handle type annotations for generics at runtime?

    Python utilizes its dynamic nature at runtime while utilizing static type hints provided through annotations during development for improved code understanding and error detection capabilities.


    Understanding how to pass a Python class by reference while initializing its types is crucial. Once you grasp concepts around “TypeVar” and familiarize yourself with how Python efficiently handles generic classes, tackling such scenarios becomes simpler yet vital in your programming journey.

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