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Python exceptions All In One

Python exceptions All In One

Different exceptions are raised for different reasons.

Common exceptions:

  • ImportError: an import fails;
  • IndexError: a list is indexed with an out-of-range number;
  • NameError: an unknown variable is used;
  • SyntaxError: the code can't be parsed properly;
  • TypeError: a function is called on a value of an inappropriate type;
  • ValueError: a function is called on a value of the correct type, but with an inappropriate value.

Python has several other built-in exceptions, such as ZeroDivisionError and OSError.
Third-party libraries also often define their own exceptions.

single except

#!/usr/bin/env python3
# coding: utf8

__author__ = 'xgqfrms'
__editor__ = 'vscode'
__version__ = '1.0.1'
__github__ = 'https://github.com/xgqfrms/Python-3.x-All-In-One'
__git__ = 'https://github.com/xgqfrms/Python-3.x-All-In-One.git'
__copyright__ = """
  Copyright (c) 2012-2050, xgqfrms; mailto:xgqfrms@xgqfrms.xyz
"""

"""

/**
 *
 * @author xgqfrms
 * @license MIT
 * @copyright xgqfrms
 * @created 2020-01-01
 * @updated 2023-06-01
 *
 * @description
 * @augments
 * @example
 * @link
 *
 */



try:
  num1 = 7
  num2 = 0
  num3 = 2
  print (num1 / num3)
  print("✅ Done calculation")
  print (num1 / num2)
except ZeroDivisionError:
  print("❌ An error occurred, due to zero division")


"""
$ py3 ./exception-handling-try-except.py

3.5
✅ Done calculation
❌ An error occurred, due to zero division

"""

image

multi except

#!/usr/bin/env python3
# coding: utf8

__author__ = 'xgqfrms'
__editor__ = 'vscode'
__version__ = '1.0.1'
__github__ = 'https://github.com/xgqfrms/Python-3.x-All-In-One'
__git__ = 'https://github.com/xgqfrms/Python-3.x-All-In-One.git'
__copyright__ = """
  Copyright (c) 2012-2050, xgqfrms; mailto:xgqfrms@xgqfrms.xyz
"""

"""

/**
 *
 * @author xgqfrms
 * @license MIT
 * @copyright xgqfrms
 * @created 2020-01-01
 * @updated 2023-06-01
 *
 * @description
 * @augments
 * @example
 * @link
 *
 */



try:
  variable = 10
  print(variable + "hello")
  print(variable / 2)
except ZeroDivisionError:
  print("❌ Divided by zero")
except (ValueError, TypeError):
  print("❌ ValueError or TypeError occurred")

"""
$ py3 ./exception-handling-try-multi-except.py

❌ ValueError or TypeError occurred

"""

finally

try:
  print("Hello World")
  print(1 / 0)
except ZeroDivisionError:
  print("❌ Divided by zero")
finally:
  print("👻 This code will run no matter what")

"""

$ py3 ./exception-handling-try-except-finally.py

Hello World
❌ Divided by zero
👻 This code will run no matter what

"""

else


try:
   print(1)
except ZeroDivisionError:
   print("❌ ZeroDivisionError")
else:
   print("✅")

try:
   print(1/0)
except ZeroDivisionError:
   print("❌❌ ZeroDivisionError")
else:
   print("✅✅")


"""
$ py3 ./exception-handling-try-except-else.py

1
✅
❌❌ ZeroDivisionError
"""

raise

# You can throw (or `raise`) exceptions when some condition occurs.
# You need to specify the `type` of the exception raised.

try:
  num = 102
  if num > 100:
    # 自定 throw error 类型
    raise ValueError
except ValueError:
  print("❌ ValueError")

# 没有处理 raise ❌
num = 102
if num > 100:
  # 自定 throw error 类型
  raise ValueError

"""
$ py3 ./exception-handling-raise.py

❌ ValueError
Traceback (most recent call last):
  File "/Users/xgqfrms-mm/Documents/github/Python-3.x-All-In-One/src/./exception-handling-raise.py", line 16, in <module>
    raise ValueError
ValueError

"""

python get exception message

Python 3

"""
You are making a program to post tweets. Each tweet must not exceed 42 characters.

Complete the program to raise an exception, in case the length of the tweet is more than 42 characters.

You can use the len() function to calculate the length of the string.

"""

tweet = input()

try:
  #your code goes here
  if(len(tweet) > 42):
    raise ValueError("tweet 超出 42 字符的最大长度限制 ❌")
    # raise SyntaxError("tweet 超出 42 字符的最大长度限制 ❌")
except Exception as err:
  print("❌ Error =", err)
  print("❌❌ Error args =", err.args)
  print("❌❌❌ Error args[0] =", err.args[0])
# except Exception, err:
  # print("❌ Error msg", err.msg)
  # print("❌❌ Error message", err.message)
else:
  print("✅ Posted")

"""

$ py3 ./exception-handling-say-something.py

###########################################
❌ Error = tweet 超出 42 字符的最大长度限制 ❌
❌❌ Error args = ('tweet 超出 42 字符的最大长度限制 ❌',)
❌❌❌ Error args[0] = tweet 超出 42 字符的最大长度限制 ❌


$ py3 ./exception-handling-say-something.py

xgqfrms
✅ Posted

"""


"""

class SyntaxError(Exception):
    msg: str
    lineno: int | None
    offset: int | None
    text: str | None
    filename: str | None
    if sys.version_info >= (3, 10):
        end_lineno: int | None
        end_offset: int | None

class SystemError(Exception): ...
class TypeError(Exception): ...
class ValueError(Exception): ...
class FloatingPointError(ArithmeticError): ...
class OverflowError(ArithmeticError): ...
class ZeroDivisionError(ArithmeticError): ...
class ModuleNotFoundError(ImportError): ...
class IndexError(LookupError): ...
class KeyError(LookupError): ...
class UnboundLocalError(NameError): ...


"""

image

Python 2

# old ❌
try:
  # ...
except Exception, e:
  # ...


# new ✅
try:
  # ...
except Exception as e:
  # ...

https://docs.python.org/zh-cn/3/library/exceptions.html

https://docs.python.org/3/tutorial/errors.html

⚠️ 注意事项:

对于 Python 3 的 Exception，与 Python 2 的 Exception 相比，有两个需要注意的地方：

  1. 在 Python 3 Exception 的 except 子句中，不支持使用逗号 ',' 分隔 Exception 和 e，所以需要采用 as 关键词进行替换；
  2. 与 Python 2 Exception 类相比，Python 3 Exception 类没有 message 成员变量。
    针对这个问题，可以使用 err.args 方法获取得到相关的异常信息。
    针对这个问题，可以使用 sys.exc_info() 方法获取得到相关的异常信息。

https://www.cnblogs.com/xgqfrms/p/17589042.html#5197603

demos

#!/usr/bin/env python3
# coding: utf8

__author__ = 'xgqfrms'
__editor__ = 'vscode'
__version__ = '1.0.1'
__github__ = 'https://github.com/xgqfrms/Python-3.x-All-In-One'
__git__ = 'https://github.com/xgqfrms/Python-3.x-All-In-One.git'
__copyright__ = """
  Copyright (c) 2012-2050, xgqfrms; mailto:xgqfrms@xgqfrms.xyz
"""

"""

/**
 *
 * @author xgqfrms
 * @license MIT
 * @copyright xgqfrms
 * @created 2020-01-01
 * @updated 2023-06-01
 *
 * @description
 * @augments
 * @example
 * @link
 *
 */



# setter/getter

class Pizza:
  def __init__(self, toppings):
    self.toppings = toppings
    self._pineapple_allowed = False

  @property
  def pineapple_allowed(self):
    return self._pineapple_allowed

  # property setter
  @pineapple_allowed.setter
  def pineapple_allowed(self, value):
    if value:
      password = input("Enter the password: ")
      if password == "123":
        self._pineapple_allowed = value
      else:
        raise ValueError("Alert! Intruder!")
  @pineapple_allowed.getter
  def pineapple_allowed(self):
    return "✅" + str(self._pineapple_allowed)

try:
  pizza = Pizza(["cheese", "tomato"])
  print(pizza.toppings)
  print(pizza._pineapple_allowed)
  print("\npizza.pineapple_allowed =", pizza.pineapple_allowed)
  pizza.pineapple_allowed = True
  print(pizza.pineapple_allowed)
except ValueError:
  print("ValueError")
finally:
  print("finished")

"""

$ py3 ./class-property-setter-getter.py

['cheese', 'tomato']
False

pizza.pineapple_allowed = ✅False
Enter the password: 123
✅True

"""

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posted @ 2023-07-28 22:23  xgqfrms  阅读(10)  评论(2)  编辑  收藏  举报