python 异常基础

• Exceptions
• • `1. try-except`
  • `2. 自定义异常`

• 知道异常类型

# 读取一个不存在的文件
file_name = 'not_existing.txt'

try:
    with open(file_name, 'r') as my_file:
        print('File is successfully open')
        
except FileNotFoundError as e:
    print('Uups, file: {} not found'.format(file_name))
    print('Exception: {} was raised'.format(e))

# Uups, file: not_existing.txt not found
# Exception: [Errno 2] No such file or directory: 'not_existing.txt' was raised

• 不知道异常类型

def calculate_division(var1, var2):
    result = 0
    
    try:
        result = var1 / var2
    except ZeroDivisionError as ex1:
        print("Can't divide by zero")
    except Exception as ex2:
        print('Exception: {}'.format(ex2))

    return result

result1 = calculate_division(3, 3)
print('result1: {}'.format(result1))  # result1: 1.0

result2 = calculate_division(3, '3')
# Exception: unsupported operand type(s) for /: 'int' and 'str'
print('result2: {}'.format(result2))  # result2: 0

result3 = calculate_division(3, 0)
# Can't divide by zero
print('result3: {}'.format(result3))  # result3: 0

• try-except也可以放在函数外部

def calculate_division(var1, var2):
    return var1 / var2

try:
    result = calculate_division(3, '3')
except Exception as e:
    print(e)

# unsupported operand type(s) for /: 'int' and 'str'

import math

# 定义自己的异常
class NegativeNumbersNotSupported(Exception):
    pass

# 实例
def secret_calculation(number1, number2):
    if number1 < 0 or number2 < 0:
        msg = 'Negative number in at least one of the parameters: {}, {}'.format(
            number1, number2)
        raise NegativeNumbersNotSupported(msg)
  
    return math.sqrt(number1) + math.sqrt(number2)

# 触发自定义异常
result = secret_calculation(-1, 1)
# NegativeNumbersNotSupported: Negative number in at least one of the parameters: -1, 1