Detailed explanation of raise keywords in Python

1. Core syntax analysis

1.1 Basic syntax form

raise [Exception type[(parameter)]]

Usage instructions：

Only exists in exception handling blocks (exceptorfinally)internal
Automatically rethrow the currently caught exception
Keep original exception stack information

1.2 Complete syntax structure

raise [Exception type[(parameter)]] [from reason]

2. Basic usage scenarios

2.1 Triggering built-in exception

# Parameter verification scenariodef calculate_square(n):
    if not isinstance(n, (int, float)):
        raise TypeError("Numerical type must be passed in")
    return n ** 2

# Call examplecalculate_square("5")  # trigger TypeError

3. Advanced usage techniques

3.1 Exception Chaining

import json

try:
    config = (open(''))
except FileNotFoundError as fnf_error:
    raise RuntimeError("Profile loading failed") from fnf_error

# Error output shows association# RuntimeError: Configuration file failed to load# The above exception was the direct cause of...

3.2 Custom exception triggers python

class NetworkTimeout(Exception):
"""Custom network timeout exception"""
	def __init__(self, host, timeout):
	     = host
	     = timeout
	    super().__init__(f"connect {host} time out（{timeout}s）")

# Trigger custom exceptionif response_time &gt; 30:
	raise NetworkTimeout("", 30)

4. Detailed explanation of special forms

4.1 No exception type throw

def deprecated_feature():
    raise "This feature is deprecated"  # ❌ Error!  An Exception instance must be thrown
# The correct way to do itdef deprecated_feature():
    raise DeprecationWarning("This feature is deprecated")

4.2 Exception parameter passing

try:
    raise ValueError("Invalid input", 404, {"detail": "Illegal ID"})
except ValueError as e:
    print()  # ('Invalid input', 404, {'detail': 'ID is illegal'})

5. Common usage modes

5.1 Defensive programming

def divide(a, b):
    if b == 0:
        raise ZeroDivisionError("The divisor cannot be zero")
    return a / b

5.2 API Error Handling

def fetch_data(url):
    response = (url)
    if 400 <= response.status_code < 500:
        raise ClientError(response.status_code, )
    elif response.status_code >= 500:
        raise ServerError(response.status_code)
    return ()

6. Best Practice Guide

6.1 Principle of exception type selection

Error scenario	Recommended exception types
Parameter type error	TypeError
Invalid parameter value	ValueError
File operation error	IOError
Business rules violations	Custom exceptions

6.2 Exception message specification

# Not recommendedraise ValueError("Error occurred")

# Recommended formatraise ValueError(f"parameter {param} Value of {value} Exceeded valid range（Allowed range：{min}~{max}）")

7. Things to note

from Parameter usage

# Show the original exception causeraise ParsingError from original_error

Performance considerations

Avoid frequent throwing of exceptions in loops
Exception processing time is determined by conditional10-100Double

Debugging Assistance

# Print the full stackimport traceback
try:
    risky_call()
except:
    traceback.print_exc()
    raise  # Re-throw

8. Comprehensive application examples

8.1 Data verification chain

def validate_user(user):
    if not ('username'):
        raise ValueError("Username Required")
    if len(user['password']) &lt; 8:
        raise SecurityError("Password at least 8 digits")
    if not (r"[^@]+@[^@]+\.[^@]+", user['email']):
        raise FormatError("Invalid mailbox format")
    return True

8.2 Context Manager

class Transaction:
    def __enter__(self):
        if not .is_valid():
            raise ConnectionError("Database connection failed")
        return self
    
    def __exit__(self, exc_type, exc_val, exc_tb):
        if exc_type:
            ()
            raise TransactionError("Transaction execution failed") from exc_val
        ()

Summarize

The above is personal experience. I hope you can give you a reference and I hope you can support me more.