python学习(十一)测试和调试

最近学习了python的错误处理和几种测试方法

`1 try except`

可以通过try except方式捕捉异常

try:

    print('try...')

    r = 10/0

    print('result is :', r)

except ZeroDiversionError as e:

    print('except is :', e)

finally:

    print('finally ...')

print('END')

　　可以捕捉不同类型的错误，编写多个except

try:

    print('try...')

    r = 10/int('a')

    print('result is: ', r)

except ValueError as e:

    print('ValueError : ', e)

except ZeroDiversionError as e:

    print('ZeroDivisionError is : ', e)

finally:

    print('finally ...')

print('END')

　　try except同样支持else结构

try:

    print('try... ')

    r = 10/int('2')

    print('result is : ', r)

except ValueError as e:

    print('ValueError : ', e)

except ZeroDivisionError as e:

    print('ZeroDivisionError is : ', e)

else:

    print('no error')

finally:

    print('finally ...')

print('END')

　　某个函数调用出现异常，在上层同样可以捕获到

def foo(s):

    return 10/int(s)

def bar(s):

    return  foo(s) * 2

def main():

    try:

        bar('0')

    except Exception as e:

        print('Exception is : ', e)

    finally:

        print('finally...')

main()

2 logging

python 提供打日志方式输出异常，并且不会因为出现异常导致程序中断

import logging

def foo(s):

    return 10/int(s)

def bar(s):

    return foo(s) * 2

def main():

    try:

        bar('0')

    except Exception as e:

        logging.exception(e)

main()

print('END')

如果想要将异常处理的更细致，可以自定义一个异常类，继承于几种错误类，如ValueError等，在可能出现问题的地方将错误抛出来

class FooError(ValueError):

    pass

def foo(s):

    n = int(s)

    if n == 0:

        raise FooError('invalid error is : %s' %s)

    return 10/n

foo('0')

　　错误可以一层一层向上抛，直到有上层能处理这个错误为止

def foo(s):

    n = int(s)

    if n==0:

        raise ValueError('invalid error is: %s' %s)

    return 10/n

def bar():

    try:

        foo('0')

    except ValueError as e:

        print('ValueError')

        raise

bar()

　　logging可以设置不同的级别,通过basicConfig可以设置

import logging

logging.basicConfig(level=logging.INFO)

def foo(s):

    n = int(s)

    return 10/n

def main():

    m = foo('0')

    logging.info('n is : %d' %m)

main()

3 断言assert

大部分语言都支持assert，python也一样，在可能出错的地方写assert，会在异常出现时使程序终止

def foo(s):

    n = int(s)

    assert n != 0 ,'n is zero'

    return 10/n

def main():

    foo('0')

main()

4 pdb调试和set_trace

pdb调试用 python -m pdb 文件名.py, 单步执行敲n,退出为q
python 可以在代码里设置断点，在程序自动执行到断点位置暂停,暂停在set_trace的代码行

import pdb

def foo(s):

    n = int(s)

    pdb.set_trace()

    return 10/n

def main():

    m = foo('0')

main()

5 单元测试

先实现一个自己定义的Dict类，将文件保存为mydict.py

class Dict(dict):

    def __init__(self, **kw):

        super(Dict, self).__init__(**kw)

    def __getattr__(self, key):

        try:

            return self[key]

        except Exception as e:

            raise AttributeError('AttributeError is :%s', e)

    def __setattr__(self, key, value):

        self[key] =  value

　　python 提供了单元测试的类，开发者可以继承unittest.Test实现特定的测试类,下面实现Dict的单元测试类，保存为unittestdict.py

import unittest

from mydict import Dict

class TestDict(unittest.TestCase):

	def setUp(self):

		print('setUp...')

	def tearDown(self):

		print('tear Down...')

	def test_init(self):

		d = Dict(a='testa', b = 1)

		self.assertEqual(d.a, 'testa')

		self.assertEqual(d.b, 1)

		self.assertTrue(isinstance(d, dict))

	def test_key(self):

		d = Dict()

		d['name'] = 'hmm'

		self.assertEqual(d.name, 'hmm')

	def test_attr(self):

		d = Dict()

		d.name = 'hmm'

		self.assertEqual(d['name'], 'hmm')

		self.assertTrue('name' in d)

	def test_attrerror(self):

		d = Dict()

		with self.assertRaises(AttributeError):

			value = d.empty

	def test_keyerror(self):

		d = Dict()

		with self.assertRaises(AttributeError):

			value = d['empty']

if __name__ == '__main__':

	unittest.main()

　　运行unittest.py可以检测mydict中Dict类是否有错误

`6 文档测试`

文档测试在代码中按照特定格式编写python输入和期待的输出，通过python提供的文档测试类，实现测试代码的目的

class Dict(dict):

	'''

	>>> d1 = Dict()

	>>> d1['x'] = 100

	>>> d1.x

	100

	>>> d1.y = 200

	>>> d1['y']

	200

	>>> d2=Dict(a=1,b=2,c='m')

	>>> d2.c

	'm'

	'''

	def __init__(self, **kw):

		super(Dict,self).__init__(**kw)

	def __getattr__(self,key):

		try:

			return self[key]

		except KeyError:

			raise AttributeError('AttributeError key is %s' %key)

	def __setattr__(self,key,value):

		self[key] = value

if __name__ == '__main__':

	import doctest

	doctest.testmod()

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