python04-错误、调试和测试

目录

1 错误处理

try…except…finally…

>>> try:    print('try...')    r=10/0    print('result:',r)except ZeroDivisionError as e:    print('except:',e)finally:    print('finally....')    print('END')try...except: division by zerofinally....END

• 函数可能会抛出ValueError，所以我们用一个except捕获ValueError，用另一个except捕获ZeroDivisionError。

此外，如果没有错误发生，可以在except语句块后面加一个else，当没有错误发生时，会自动执行else语句

>>> try:    print('try...')    r = 10 / int('a')    print('result:', r)except ValueError as e:    print('ValueError:', e)except ZeroDivisionError as e:    print('ZeroDivisionError:', e)finally:    print('finally...')try...ValueError: invalid literal for int() with base 10: 'a'finally...

• 常见的错误类型
  
  • https://docs.python.org/3/library/exceptions.html#exception-hierarchy
• 使用try…except捕获错误还有一个巨大的好处，就是可以跨越多层调用

>>> def foo(s):    return 10 / int(s)>>> def bar(s):    return foo(s) * 2>>> def main():    try:        bar('0')    except Exception as e:        print('Error:', e)    finally:        print('finally...')

抛出错误

• raise

>>> def a(m,n):    if n==0:        raise('the division is o')    return m/n>>> a(10,2)5.0>>> a(10,0)Traceback (most recent call last):  File "<pyshell#306>", line 1, in <module>    a(10,0)  File "<pyshell#304>", line 3, in a    raise('the division is o')TypeError: exceptions must derive from BaseException>>> def aa():    try:        a(10,0)    except ValueError as e:        print('ValuError!')        raise>>> aa()Traceback (most recent call last):  File "<pyshell#314>", line 1, in <module>    aa()  File "<pyshell#313>", line 3, in aa    a(10,0)  File "<pyshell#304>", line 3, in a    raise('the division is o')TypeError: exceptions must derive from BaseException>>> 

2 调试

print 和assert

• 方式简单粗暴

def foo(s):    n = int(s)    print('>>> n = %d' % n)    return 10 / n

- 凡是用print()来辅助查看的地方，都可以用断言（assert）来替代- assert的意思是，表达式n != 0应该是True，否则，根据程序运行的逻辑，后面的代码肯定会出错。如果断言失败，assert语句本身就会抛出AssertionError

def foo(s):    n = int(s)    assert n != 0, 'n is zero!'    return 10 / ndef main():    foo('0')

logging

• 把print()替换为logging是第3种方式，和assert比，logging不会抛出错误，而且可以输出到文件

>>> import logging>>> logging.basicConfig(level=logging.INFO)>>> s='0'>>> n=int(s)>>> logging.info('n=%d' %n)INFO:root:n=0

pdb

IDE

• PyCharm

3 单元测试

4 文档测试

本学习笔记参考http://www.liaoxuefeng.com/