With errors and exceptions in Python, we will encounter errors when programming as well as when running programs. In Python, we can divide errors into 2 types: syntax error and exception.
1. Syntax Error in Python
One of the errors and exceptions in Python is Syntax error also called parsing error. This error occurs because we do not follow the syntax of Python when programming. Syntax error usually occurs when we start learning Python and do not understand Python syntax well.
Example of Syntax Error in Python
# SyntaxError: expected ':'
if a < 3
print("a is smaller than 3")In the example above, the if statement is missing ‘:‘, causing a syntax error.
# SyntaxError: invalid syntax
while True:
print(Hello world)In the example above, the argument of the print function is not enclosed in quotes, causing a syntax error.
2. Exception Error in Python
Another error and exception in Python are Runtime errors are called exceptions or logical errors. Many cases can cause exceptions. For example, when we open a non-existent file, we encounter an exception called FileNotFoundError. Or dividing a number by 0 will encounter an exception called ZeroDivisionError. Or if we import a non-existent module, we will encounter an exception called ImportError.
When an exception occurs, Python creates an exception object. Python will stop the program and print error messages if these exceptions are not handled.
# ZeroDivisionError: division by zero
x = 1/0
# NameError: name 'spam' is not defined
y = 4 + spam*3
# TypeError: can only concatenate str (not "int") to str
z = '2' + 2
# FileNotFoundError: [Errno 2] No such file or directory: 'imaginary.txt'
open("imaginary.txt")3. Built-in Exceptions in Python
Many built-in exceptions in Python catch exceptions. We can use the print(dir(locals()['__builtins__'])) command to see the built-in exceptions in Python.
The table below is a list of some common built-in exceptions in Python.
| Exception | Cause of the exception |
|---|---|
| AssertionError | Returns an exception when the comparison expression of the assert statement has a result of False |
| FloatingPointError | Error occurs when performing operations on floating-point values |
| ImportError | Occurs when importing a module that Python cannot find |
| IndexError | Occurs when accessing an element with an index outside the allowed range |
| KeyError | Occurs when a key is not found in a Dictionary |
| KeyboardInterrupt | When users type interrupt keys (Ctrl+C or Delete) |
| MemoryError | Occurs when the storage memory is full |
| NameError | Occurs when a variable is not found in the local or global scope |
| NotImplementedError | Occurs when an abstract method of a base class is not redefined in a derived class |
| OSError | These are system errors of the operating system |
| OverflowError | Occurs when the result of a calculation gives a value too large to be stored and represented |
| RuntimeError | Occurs when an exception does not belong to any pre-built exception in Python |
| SyntaxError | Occurs when the syntax of Python is not correct |
| IndentationError | Occurs when using indentation incorrectly |
| TabError | Occurs when using tabs or inconsistent spaces |
| SystemError | Occurs when the interpreter detects some internal error |
| TypeError | Occurs when a method or operator is applied to an object with an inappropriate data type |
| UnboundLocalError | Occurs when assigning a value (reference) to a local variable in a method but there is no value that the variable refers to |
| UnicodeError | Occurs when encoding or decoding related to Unicode is corrupted |
| ValueError | A function has arguments passed in the correct data type but the value of the argument is inappropriate |
| ZeroDivisionError | Dividing a number by 0 |