Types of Errors

Errors are supposed to happen: input given not of set datatype, dividing by zero, and more. It is important to learn what is the error and how to avoid it for debugging. In Python, errors are broadly categorized into syntax errors and exceptions (runtime errors).

Below is a list of common error types:

Syntax Errors

These occur when Python encounters incorrect syntax in the code.

print("Hello" # Missing closing parenthesis

Error: SyntaxError: unexpected EOF while parsing

Exceptions (Runtime Errors)

These occur while the program is running.

NameError

Occurs when trying to use a variable that hasn’t been defined.

print(my_variable)  # my_variable is not defined

Error: NameError: name 'my_variable' is not defined

TypeError

Occurs when an operation is performed on an incompatible data type.

print("Hello" + 5)  # String and integer cannot be concatenated

Error: TypeError: can only concatenate str (not "int") to str

ValueError

Occurs when a function receives an argument of the correct type but an inappropriate value.

int("hello")  # Cannot convert a non-numeric string to an integer

Error: ValueError: invalid literal for int() with base 10: 'hello'

IndexError

Occurs when trying to access an index that does not exist in a list.

numbers = [1, 2, 3]
print(numbers[5])  # Index out of range

Error: IndexError: list index out of range

KeyError

Occurs when trying to access a non-existent key in a dictionary.

my_dict = {"name": "Jasmeet"}
print(my_dict["age"])  # "age" key does not exist

Error: KeyError: 'age'

AttributeError

Occurs when an invalid attribute is accessed for an object.

num = 10
num.append(5)  # Integers do not have an 'append' method

Error: AttributeError: 'int' object has no attribute 'append'

ZeroDivisionError

Occurs when attempting to divide by zero.

print(10 / 0)  # Division by zero is not allowed

Error: ZeroDivisionError: division by zero

FileNotFoundError

Occurs when attempting to open a file that does not exist.

with open("missing_file.txt", "r") as file:
    content = file.read()

Error: FileNotFoundError: [Errno 2] No such file or directory: 'missing_file.txt'

ImportError / ModuleNotFoundError

Occurs when trying to import a module that doesn’t exist or isn’t installed.

import non_existent_module

Error: ModuleNotFoundError: No module named 'non_existent_module'

IndentationError

Occurs when indentation is incorrect in a Python script.

def my_function():
print("Hello")  # Missing indentation

Error: IndentationError: expected an indented block

Other Common Exceptions

• MemoryError – When the system runs out of memory.
• OverflowError – When a numerical operation exceeds the limit.
• RuntimeError – When an operation fails for an unspecified reason.
• AssertionError – Raised when an assert statement fails.