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Error Handing in Python | try except in Python

Last updated Apr 25, 2024

In Python, the try and except blocks are used for error handling, allowing you to catch and handle exceptions (errors) that may occur during the execution of your code.

Here's how the try and except blocks work in Python:

try:
    # Code that may raise an exception
    result = 5 / 0  # This will raise an exception
except Exception as e:
    # Code to handle other exceptions
    print(f"An error occurred: {e}")

In this example, the try block contains the code that might raise an exception. The except block catches and handles exceptions. The Exception class is a built-in Python class that serves as a base class for all exceptions. By specifying Exception, you are catching any exception that inherits from the Exception class.

The output of the above code is as follows:

An error occurred: division by zero

Handling Multiple Exceptions

A try statement may have multiple except blocks for handling different exceptions. The code inside the first matching except block is executed.

Example:

try:
    # Code that may raise an exception
    result = 5 / 0  # This will raise an exception
except ZeroDivisionError:
    # Code to handle the specific exception
    print("Error: Division by zero")
except Exception as e:
    # Code to handle other exceptions
    print(f"An error occurred: {e}")
else:
    # Optional block for code that should run when no exceptions are raised
    print("No exceptions occurred.")

Output:

Error: Division by zero

Python Built-in Exceptions

The table below displays a list of built-in exceptions in Python:

Exception	Cause of Error
ArithmeticError	Raised when an arithmetic operation fails.
AssertionError	Raised when an assert statement fails.
AttributeError	Raised when an attribute referrence or assignment fails.
EOFError	Raised when the built-in function input() or raw_input() hits end-of-file condition.
FloatingPointError	Raised when a floating-point operation fails.
GeneratorExit	Raised when a generator or coroutine is closed.
ImportError	Raised when an import fails.
IndexError	Raised when an trying to access index that is out of range.
KeyError	Raised when trying to read a mapping key that does not exists in a set of existings keys.
KeyboardInterrupt	Raised when a user presses the interrupt key (Crtl+C or Delete).
MemoryError	Raised when the program runs out of memory.
NameError	Raised when a variable is not found in global or local scope.
NotImplementedError	Raised when overriding the abstract methods in a user-defined class.
OSError	Raised due to system-related error return by system functions.
OverflowError	Raised when the result of an arithmetic operation is too big.
ReferenceError	Raised when a weak reference proxy is used to access the referent after the garbage collection.
RuntimeError	Raised when an unspecified error occurs.
StopIteration	Raised when an the built-in next() function is called to indicate that no item is left to be return by an iterator.
SyntaxError	Raised when there is a syntax error.
IndentationError	Raised due to incorrect identation in the code.
TabError	Raised due to incorrect number of tabs and spaces.
SystemError	Raised due to internal error in the Python interpreter.
SystemExit	Raised when the sys.exit() function is called.
TypeError	Raised due to inappropriate argument type.
UnboundLocalError	Raised when a reference is made to a local variable that has not been assigned any value inside a method or function.
UnicodeError	Raised when a Unicode related error occurs.
UnicodeEncodeError	Raised when a Unicode encoding error occurs.
UnicodeDecodeError	Raised when a Unicode decoding error occurs.
UnicodeTranslateError	Raised when a Unicode-related error occurs during translation.
ValueError	Raised when an argument of a function receives the value of another incorrect type.
ZeroDivisionError	Raised when trying to divide a value by 0