Why Do I Get `TypeError` or `AttributeError` When Defining a Python Class Constructor?

Mismatched Underscores in Class Constructor Name

In Python, it's common to encounter errors when creating classes due to mismatched underscores in the class constructor name. Instead of "def __int__" or "def _init_", the correct syntax should be "def __init__" with two underscores on each side.

TypeError: Class Method Takes No Arguments

If the class constructor doesn't take any arguments, you may encounter a TypeError stating that the class "takes no arguments". This occurs because the "__int__" method with mismatched underscores is syntactically valid but not a valid class constructor. As a result, Python falls back to the base object constructor, which doesn't take arguments.

AttributeError: Attribute Missing from Class Instance

Alternatively, if the class constructor takes arguments but doesn't properly initialize attributes, you may encounter an AttributeError when attempting to access those attributes. This is because the "_init_" method with mismatched underscores doesn't correctly initialize the attributes.

Explanation of Exception Messages

• TypeError indicates a problem with the types of arguments or parameters in a function or class constructor.
• AttributeError indicates that an object doesn't have the specified attribute.

Prevention and Mitigation

To avoid these errors, use the correct spelling and syntax for the class constructor, which is "def __init__(self, ...)" with two underscores on each side. Proofreading and careful attention to detail can help prevent these typos. Additionally, using a convention of placing "__init__" as the first method in a class can serve as a reminder of its correct implementation.

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