Python Errors and Built-in Exceptions

In this tutorial, you will find out about various sorts of errors and exceptions that are built-in Python. They are raised at whatever point the Python interpreter encounters errors.

We can make certain mistakes while writing a program that leads to blunders when we attempt to run it. A python program ends when it experiences an unhandled mistake. These mistakes can be extensively characterized into two classes:

1. Syntax errors

2. Logical errors (Exceptions)

Python Syntax Errors

Mistake brought about by not following the correct structure (linguistic structure) of the language is called punctuation blunder or parsing error.

Let’s look at one example:

>>> if a < 3
  File "<interactive input>", line 1
    if a < 3
           ^
SyntaxError: invalid syntax

As shown in the example, an arrow indicates where the parser ran into the syntax error.

We can notice here that a colon: is missing in the if statement.

Python Logical Errors (Exceptions)

Errors that happen at runtime (in the wake of breezing through the linguistic structure assessment) are called exceptions or logical errors.

For example, they happen when we attempt to open a file(for perusing) that doesn’t exist (FileNotFoundError), attempt to separate a number by zero (ZeroDivisionError) or attempt to import a module that doesn’t exist (ImportError).

Whenever these sorts of runtime errors happen, Python makes an exception object. If not taken care of appropriately, it prints a traceback to that blunder alongside certain insights regarding why that error occurred.

Let’s look at how Python treats these errors:

>>> 1 / 0
Traceback (most recent call last):
 File "<string>", line 301, in runcode
 File "<interactive input>", line 1, in <module>
ZeroDivisionError: division by zero

>>> open("imaginary.txt")
Traceback (most recent call last):
 File "<string>", line 301, in runcode
 File "<interactive input>", line 1, in <module>
FileNotFoundError: [Errno 2] No such file or directory: 'imaginary.txt'

Python Built-in Exceptions

Illegal operations can raise special cases. There are plenty of built-in exceptions in Python that are raised while comparing blunders happen. We can see all the inherent special cases using the built-in local() function as follows:

print(dir(locals()['__builtins__']))

locals()[‘__builtins__’] will return a module of built-in exceptions, functions, and attributes. dir allows us to list these attributes as strings.

Some of the common built-in exceptions in Python programming along with the error that causes them are listed below:

Exception	Cause of Error
AssertionError	Raised when an assert statement fails.
AttributeError	Raised when attribute assignment or reference fails.
EOFError	Raised when the input() function hits end-of-file condition.
FloatingPointError	Raised when a floating-point operation fails.
GeneratorExit	Raise when a generator’s close() method is called.
ImportError	Raised when the imported module is not found.
IndexError	Raised when the index of a sequence is out of range.
KeyError	Raised when a key is not found in a dictionary.
KeyboardInterrupt	Raised when the user hits the interrupt key (Ctrl+C or Delete).
MemoryError	Raised when an operation runs out of memory.
NameError	Raised when a variable is not found in the local or global scope.
NotImplementedError	Raised by abstract methods.
OSError	Raised when system operation causes the system-related error.
OverflowError	Raised when the result of an arithmetic operation is too large to be represented.
ReferenceError	Raised when a weak reference proxy is used to access a garbage collected referent.
RuntimeError	Raised when an error does not fall under any other category.
StopIteration	Raised by next() function to indicate that there is no further item to be returned by the iterator.
SyntaxError	Raised by the parser when a syntax error is encountered.
IndentationError	Raised when there is incorrect indentation.
TabError	Raised when indentation consists of inconsistent tabs and spaces.
SystemError	Raised when the interpreter detects the internal error.
SystemExit	Raised by sys.exit() function.
TypeError	Raised when a function or operation is applied to an object of the incorrect type.
UnboundLocalError	Raised when a reference is made to a local variable in a function or method, but no value has been bound to that variable.
UnicodeError	Raised when a Unicode-related encoding or decoding error occurs.
UnicodeEncodeError	Raised when a Unicode-related error occurs during encoding.
UnicodeDecodeError	Raised when a Unicode-related error occurs during decoding.
UnicodeTranslateError	Raised when a Unicode-related error occurs during translating.
ValueError	Raised when a function gets an argument of correct type but improper value.
ZeroDivisionError	Raised when the second operand of division or modulo operation is zero.

If required, we can also define our own exceptions in Python. To learn more about them, visit Python User-defined Exceptions.

We can handle these built-in and user-defined exceptions in Python using try, except and finally statements. To learn more about them, visit Python try, except and finally statements.

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