Error handling

try,except,finally

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! ')
finally:
    print('finally... ')
print('END')
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try...
result: 5.0
no error!
finally...
END
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An exception is thrown

IOError: input/output exceptions; ImportError: Unable to import modules or packages; IndentationError: IndentationError; KeyError: attempts to access a key that does not exist in the dictionary AttributeError: attempts to access an attribute that does not exist in the object TypeError: type mismatch ValueError: Passing in a value that the caller does not expect, even if the value is of the correct type

Exceptions themselves are also classes

class FooError(ValueError) :# define exception
    pass

def foo(s) :
    n = int(s)
    if n==0:
        raise FooError('Invalid value: %s' % s)Throw an exception
    return 10 / n

foo('0')
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--------------------------------------------------------------------------- FooError Traceback (most recent call last) <ipython-input-10-0c3ece3b8a4a> in <module> 8 return 10 / n 9 ---> 10 foo('0') <ipython-input-10-0c3ece3b8a4a> in foo(s) 5 n= int(s) 6 if n==0: ----> 7 Raise FooError(' Invalid value: %s' %s)# raise exception 8 return 10 / n 9 FooError: invalid value: 0Copy the code

Using Rasie without any content directly throws an error

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 Continue to throw the current error

bar()
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ValueError! --------------------------------------------------------------------------- ValueError Traceback (most recent call last) <ipython-input-11-2304461f3f2b> in <module> 12 raise # continue to raise the current error 13 --> 14 bar() <ipython-input-11-2304461f3f2b> in bar() 7 def bar(): 8 try: ----> 9 foo('0') 10 except ValueError as e: 11 print('ValueError! ') <ipython-input-11-2304461f3f2b> in foo(s) 2 n = int(s) 3 if n==0: ----> 4 raise ValueError('invalid value: %s' % s) 5 return 10 / n 6 ValueError: invalid value: 0Copy the code

assertassertions

def foo(s) :
    n = int(s)
    assertn ! =0.'n is zero! '
    return 10 / n

foo('0')
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--------------------------------------------------------------------------- AssertionError Traceback (most recent call last) <ipython-input-24-1d060d98ffe3> in <module> 4 return 10 / n 5 ----> 6 foo('0') <ipython-input-24-1d060d98ffe3> in foo(s) 1 def foo(s): 2 n = int(s) ----> 3 assert n ! = 0, 'n is zero! ' 4 return 10 / n 5 AssertionError: n is zero!Copy the code

loggingThe module

It only works when the file is running. Interactive mode is not displayed

import loggingImport the logging package
logging.basicConfig(level=logging.INFO)Set the log output level to INFO

logging.info('123456')# output
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INFO:root:n = 0
Traceback (most recent call last):
  File "test.py", line 7, in <module>
    print(10 / n)
ZeroDivisionError: division by zero
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Unit testing

Start by writing a class to be tested

class Dict(dict) :
    def __init__(self, **kw) :
        super().__init__(**kw)

    def __getattr__(self, key) :
        try:
            return self[key]
        except KeyError:
            raise AttributeError(r"'Dict' object has no attribute '%s'" % key)

    def __setattr__(self, key, value) :
        self[key] = value

# It can be used as follows
d = Dict(a=1, b=2)
print(d['a'])
print(d.b)
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1
2
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Write unit test classes

import unittest Import the unit test module

class TestDict(unittest.TestCase) :Write a unittest class that inherits unittest.testcase

    Write unit test methods that must begin with test
    def test_init(self) :
        d = Dict(a=1, b='test')
        self.assertEqual(d.a, 1)#unittest.TestCase built-in assertion method
        self.assertEqual(d.b, 'test')
        self.assertTrue(isinstance(d, dict))

    def test_key(self) :
        d = Dict()
        d['key'] = 'value'
        self.assertEqual(d.key, 'value')

    def test_attr(self) :
        d = Dict()
        d.key = 'value'
        self.assertTrue('key' in d)
        self.assertEqual(d['key'].'value')

    def test_keyerror(self) :
        d = Dict(a)with self.assertRaises(KeyError):#unittest.TestCase expects to raise KeyError
            value = d['empty']

    def test_attrerror(self) :
        d = Dict(a)with self.assertRaises(AttributeError):#unittest.TestCase expects an AttributeError to be thrown
            value = d.empty
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Running unit tests

Method 1

if __name__ == '__main__':
    unittest.main()
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Method 2

On the command line, type python -m unittest XXX, where XXX is the file name without the suffix py

Two special methods in unit testssetUpwithtearDown

class TestDict1(unittest.TestCase) :

    def setUp(self) :
        print('setUp... ')

    def tearDown(self) :
        print('tearDown... ')
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