Python Programming Types Of Errors And Exceptions Complete Guide

Top 10 Questions and Answers: Python Programming Types of Errors and Exceptions

1. What are the main types of errors encountered in Python?

Answer: Python主要有三种主要的错误类型：

• Syntax Errors: 语法错误发生当Python解释器不能识别你的代码，因为它不符合Python的语法规则。例如，未闭合的括号，拼写错误等。
• Runtime Errors: 运行时错误又称为异常(Exception)，在程序运行过程中发生了错误，导致程序异常终止。例如，尝试访问一个不存在的文件或使用零作为除数。
• Logical Errors: 逻辑错误也称语义错误，程序语法上正确但逻辑上出错。这意味着代码运行，但从不按预期执行。例如，算法错误，错误的变量初始化等。

2. What is the difference between syntax errors and exceptions?

Answer:

• Syntax Errors occur before the program runs. They indicate something wrong with the code's structure, like a missing parenthesis or incorrect indentation. The error must be fixed before the program can start.
• Exceptions, on the other hand, are detected during execution. They usually are caused by an invalid operation, such as dividing by zero or accessing a file that doesn't exist. While syntax errors result in the program not running at all, exceptions can be caught and handled, allowing the program to continue running.

3. What are some common built-in exceptions in Python?

Answer: Python provides several built-in exceptions that cover typical error situations. Some of the common ones include:

• ZeroDivisionError: Occurs when division by zero is attempted.
• TypeError: Raised when an operation or function is applied to an object of inappropriate type.
• ValueError: Raised when a function's argument is of the right type but inappropriate value.
• FileNotFoundError: Raised when trying to access a file that does not exist.
• IndexError: Happens when trying to access an index that is out of the range of a list or other sequence data types.
• KeyError: Raised when a dictionary key is not found.
• ImportError: Happens when a module cannot be found when you try to import it.

4. How can you handle exceptions in Python?

Answer: Python uses the try, except, else, and finally blocks to handle exceptions. Here's a basic usage:

try:
    # Code that may cause an exception
    result = 10 / 0
except ZeroDivisionError:
    # Handling the exception
    print("Cannot divide by zero.")
else:
    # Code to execute if there's no exception
    print(f"The result is {result}.")
finally:
    # Code to execute regardless of whether an exception occurred or not
    print("Execution completed.")

5. What is the benefit of using a finally block in exception handling?

Answer: The finally block in Python is crucial because it executes code no matter what happens in the try and except blocks. This is particularly useful for cleaning up resources, like closing files or network connections, regardless of whether an exception occurred or not.

6. How can you raise exceptions in Python?

Answer: You can raise exceptions in Python using the raise keyword. This statement allows you to force an exception to occur at a specific point in the program. Here is an example:

def validate_age(age):
    if age < 0:
        raise ValueError("Age cannot be negative.")
    print(f"Age is valid: {age}")

try:
    validate_age(-5)
except ValueError as e:
    print(e)  # Output: Age cannot be negative.

7. What is a custom exception in Python?

Answer: Custom exceptions, also known as user-defined exceptions, allow you to define your own types of exceptions that better represent the specific error conditions of your application. Here is how you can create and use a custom exception:

class NegativeAgeError(Exception):
    """Exception raised for errors in the input age."""
    def __init__(self, age, message="Age cannot be negative."):
        self.age = age
        self.message = message
        super().__init__(self.message)

def check_age(age):
    if age < 0:
        raise NegativeAgeError(age)
    return f"Age is valid: {age}."

try:
    print(check_age(-5))
except NegativeAgeError as e:
    print(e)  # Output: Age cannot be negative.

8. How can you handle multiple exceptions in a single except block?

Answer: You can handle multiple exceptions in a single except block by using parentheses to group the exception types:

try:
    # Code that may cause an exception
    result = int("Hello")
except (ValueError, TypeError) as e:
    # Handling the exception
    print(f"An error occurred: {e}")

Alternatively, you can use multiple except blocks to handle different exceptions separately.

9. What is the purpose of the else block in the exception handling structure?

Answer: The else block in Python's exception handling structure executes if and only if the try block does not raise an exception. This means that if no exceptions occur within the try block, the else block is executed, allowing you to separate code that runs normally from code that handles exceptions.

10. Can exceptions be chained in Python?

Answer: Yes, Python allows for exception chaining, which is useful when you want to catch one exception and raise another one based on it. The raise ... from ... syntax is used for chaining exceptions:

def nested_function():
    raise ValueError("Invalid value in nested function.")

try:
    nested_function()
except ValueError as e:
    raise TypeError("Invalid type. Original error message: " + str(e)) from e

In this example, a ValueError is caught and re-raised as a TypeError, while preserving the original exception information.