011 python语法_错误处理 try except finally raise

'''
时间：2018/11/03
目录: 
　　一: 正常执行
        1 正常
        2 else
　　二: 发生错误
        1 异常
        2 异常
    三: BaseException
    四: 多层错误 - 多层捕获
    五: 记录错误
    六: 抛出错误
'''

一: 正常执行
　　1 正常

# coding:utf-8


try:
    print("try...")
    r = 10 / 2                    # 正常执行
    print("result:", r)
except ZeroDivisionError as e:
    print("except:", e)
finally:
    print("finally...")
print("END")

try...
result: 5.0
finally...
END

　　2 else

# coding:utf-8


try:
    print('try...')
    r = 10 / int('2')
    print('result:', r)
except ValueError as e:
    print('ValueError:', e)
except ZeroDivisionError as e:
    print('ZeroDivisionError:', e)
else:
    print('no error!')      # 没有错误 - 执行else
finally:
    print('finally...')
print('END')

try...
result: 5.0
no error!
finally...
END

二: 发生错误
　　1 异常

# coding:utf-8


try:
    print("try...")
    r = 10 / 0                    # 发生异常
    print("result:", r)
except ZeroDivisionError as e:    # 除法错误
    print("except:", e)
finally:
    print("finally...")
print("END")

try...
except: division by zero
finally...
END

　　2 异常

# coding:utf-8


try:
    print('try...')
    r = 10 / int('a')
    print('result:', r)
except ValueError as e:               # 变量错误
    print('ValueError:', e)
except ZeroDivisionError as e:        # 除法错误
    print('ZeroDivisionError:', e)
finally:
    print('finally...')
print('END')

try...
ValueError: invalid literal for int() with base 10: 'a'
finally...
END

三: BaseException

# coding:utf-8

def foo():
    return 10 / 0

try:
    foo()
except BaseException as e:            # 所有错误
    print('BaseException', e)
except ZeroDivisionError as e:        # 除法错误
    print('ZeroDivisionError:', e)
except ValueError as e:               # 变量错误
    print('ValueError', e)
except UnicodeError as e:             # 编码错误
    print('UnicodeError', e)

BaseException division by zero

1 :  BaseException接管 - 除法错误

# coding:utf-8

def foo():
    return 10 / int('a')

try:
    foo()
except BaseException as e:            # 所有错误
    print('BaseException', e)
except ZeroDivisionError as e:        # 除法错误
    print('ZeroDivisionError:', e)
except ValueError as e:               # 变量错误
    print('ValueError', e)
except UnicodeError as e:             # 编码错误
    print('UnicodeError', e)

BaseException invalid literal for int() with base 10: 'a'

1 :  BaseException接管 - 变量错误

1 :  python3.6.7 错误类型的继承关系。

四: 多层错误 - 多层捕获

# coding:utf-8


def foo(s):
    return 10 / int(s)

def bar(s):
    return foo(s) * 2

def main():
    try:
        print("try...")
        bar('0')
        print("try...end")
    except Exception as e:
        print('Error:', e)
    finally:
        print('finally...')

main()

1 :  try...except... 跨越多层调用。

# coding:utf-8

def foo(s):
    return 10 / int(s)

def bar(s):
    return foo(s) * 2

def main():
    bar('0')

main()

Traceback (most recent call last):
  File "D:/ProgramTools/PyCharm 5.0.4/PycharmProject/python_get/study001/study001.py", line 12, in <module>
    main()
  File "D:/ProgramTools/PyCharm 5.0.4/PycharmProject/python_get/study001/study001.py", line 10, in main
    bar('0')
  File "D:/ProgramTools/PyCharm 5.0.4/PycharmProject/python_get/study001/study001.py", line 7, in bar
    return foo(s) * 2
  File "D:/ProgramTools/PyCharm 5.0.4/PycharmProject/python_get/study001/study001.py", line 4, in foo
    return 10 / int(s)
ZeroDivisionError: division by zero

1 :  如果错误没被程序捕获，最终会被python解释器捕获

五: 记录错误

# coding:utf-8


import logging

def foo(s):
    return 10 / int(s)

def bar(s):
    return foo(s) * 2

def main():
    try:
        print("try...")
        bar('0')
        print("try...end")
    except Exception as e:
        print("except...")
        logging.exception(e)
    finally:
        print("finally...")

main()
print('END')

try...
except...
finally...
END
ERROR:root:division by zero
Traceback (most recent call last):
  File "D:/ProgramTools/PyCharm 5.0.4/PycharmProject/python_get/study001/study001.py", line 14, in main
    bar('0')
  File "D:/ProgramTools/PyCharm 5.0.4/PycharmProject/python_get/study001/study001.py", line 9, in bar
    return foo(s) * 2
  File "D:/ProgramTools/PyCharm 5.0.4/PycharmProject/python_get/study001/study001.py", line 6, in foo
    return 10 / int(s)
ZeroDivisionError: division by zero

1 :  logging模块可以让程序继续执行，并记录错误信息，把错误记录到日志文件里。

六: 抛出错误

# coding:utf-8

def foo(s):
    n = int(s)
    if n==0:
        raise ValueError('invalid value: %s' % s)
    return 10 / n

def bar():
    try:
        foo('0')
    except ValueError as e:
        print('ValueError!')
        raise   # 捕获错误 - 暂不处理

bar()

ValueError!
  File "D:/ProgramTools/PyCharm 5.0.4/PycharmProject/python_get/study001/study001.py", line 16, in <module>
    bar()
  File "D:/ProgramTools/PyCharm 5.0.4/PycharmProject/python_get/study001/study001.py", line 11, in bar
    foo('0')
  File "D:/ProgramTools/PyCharm 5.0.4/PycharmProject/python_get/study001/study001.py", line 6, in foo
    raise ValueError('invalid value: %s' % s)
ValueError: invalid value: 0