python异常处理之 traceback 解析示例

àì夳堔傛蜴生んèń 2022-05-31 00:42 325阅读 0赞

** python异常处理之 traceback 解析示例**

**其中，cgitb适合在开发的过程中进行调试，而logging适合在线上环境使用，二者都非常方便；**

**(1)Python中的异常栈跟踪**

def func(a, b):
        return a / b
    if __name__ == '__main__':
        import sys
        import traceback
        try:
            func(1, 0)
        except Exception as e:
            print "print exc"
            traceback.print_exc(file=sys.stdout)

输出：

print exc
    Traceback (most recent call last):
      File "/Users/a6/test_exception_process.py", line 34, in <module>
        func(1, 0)
      File "/Users/a6/test_exception_process.py", line 29, in func
        return a / b
    ZeroDivisionError: integer division or modulo by zero

**其实traceback.print\_exc()函数只是traceback.print\_exception()函数的一个简写形式，而它们获取异常相关的数据都是通过sys.exc\_info()函数得到的。**

def func(a, b):
        return a / b
    if __name__ == '__main__':
        import sys
        import traceback
        try:
            func(1, 0)
        except Exception as e:
            print "print_exception()"
            exc_type, exc_value, exc_tb = sys.exc_info()
            print 'the exc type is:', exc_type
            print 'the exc value is:', exc_value
            print 'the exc tb is:', exc_tb
            traceback.print_exception(exc_type, exc_value, exc_tb)

输出：

print_exception()
    the exc type is: <type 'exceptions.ZeroDivisionError'>
    the exc value is: integer division or modulo by zero
    the exc tb is: <traceback object at 0x10acc9dd0>
    Traceback (most recent call last):
      File "/Users/a6/Downloads/PycharmProjects/speiyou_di_my/hive/shuangshi_haibian/test_exception_process.py", line 49, in <module>
        func(1, 0)
      File "/Users/a6/Downloads/PycharmProjects/speiyou_di_my/hive/shuangshi_haibian/test_exception_process.py", line 44, in func
        return a / b
    ZeroDivisionError: integer division or modulo by zero

**sys.exc\_info()返回的值是一个元组，其中第一个元素，exc\_type是异常的对象类型，exc\_value是异常的值，exc\_tb是一个traceback对象，对象中包含出错的行数、位置等数据。然后通过print\_exception函数对这些异常数据进行整理输出。 **  
**(2)traceback模块提供了extract\_tb函数来更加详细的解释traceback对象所包含的数据：**

def func(a, b):
        return a / b
    if __name__ == '__main__':
        import sys
        import traceback
        try:
            func(1, 0)
        except:
            _, _, exc_tb = sys.exc_info()
            for filename, linenum, funcname, source in traceback.extract_tb(exc_tb):
                print "%-23s:%s '%s' in %s()" % (filename, linenum, source, funcname)

输出：

/Users/a6/test_exception_process.py:67 'func(1, 0)' in <module>()
    /Users/a6/test_exception_process.py:62 'return a / b' in func()

**(3)使用cgitb来简化异常调试**

**如果平时开发喜欢基于log的方式来调试，那么可能经常去做这样的事情，在log里面发现异常之后，因为信息不足，那么会再去额外加一些debug log来把相关变量的值输出。调试完毕之后再把这些debug log去掉。其实没必要这么麻烦，Python库中提供了cgitb模块来帮助做这些事情，它能够输出异常上下文所有相关变量的信息，不必每次自己再去手动加debug log。   
cgitb的使用简单的不能想象:**

def func(a, b):
        return a / b
    if __name__ == '__main__':
        import cgitb
    
        cgitb.enable(format='text')
        import sys
        func(1, 0)

输出：

/System/Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7 /Users/a6/test_exception_process.py
    <type 'exceptions.ZeroDivisionError'>
    Python 2.7.10: /System/Library/Frameworks/Python.framework/Versions/2.7/Resources/Python.app/Contents/MacOS/Python
    Thu Feb  1 16:58:32 2018
    
    A problem occurred in a Python script.  Here is the sequence of
    function calls leading up to the error, in the order they occurred.
    
     /Users/a6/test_exception_process.py in <module>()
       79     cgitb.enable(format='text')
       80     import sys
       81     func(1, 0)
       82 
       83 
    func = <function func>
    
     /Users/a6/test_exception_process.py in func(a=1, b=0)
       73 
       74 def func(a, b):
       75     return a / b
       76 if __name__ == '__main__':
       77     import cgitb
    a = 1
    b = 0
    <type 'exceptions.ZeroDivisionError'>: integer division or modulo by zero
        __class__ = <type 'exceptions.ZeroDivisionError'>
        __delattr__ = <method-wrapper '__delattr__' of exceptions.ZeroDivisionError object>
        __dict__ = {}
        __doc__ = 'Second argument to a division or modulo operation was zero.'
        __format__ = <built-in method __format__ of exceptions.ZeroDivisionError object>
        __getattribute__ = <method-wrapper '__getattribute__' of exceptions.ZeroDivisionError object>
        __getitem__ = <method-wrapper '__getitem__' of exceptions.ZeroDivisionError object>
        __getslice__ = <method-wrapper '__getslice__' of exceptions.ZeroDivisionError object>
        __hash__ = <method-wrapper '__hash__' of exceptions.ZeroDivisionError object>
        __init__ = <method-wrapper '__init__' of exceptions.ZeroDivisionError object>
        __new__ = <built-in method __new__ of type object>
        __reduce__ = <built-in method __reduce__ of exceptions.ZeroDivisionError object>
        __reduce_ex__ = <built-in method __reduce_ex__ of exceptions.ZeroDivisionError object>
        __repr__ = <method-wrapper '__repr__' of exceptions.ZeroDivisionError object>
        __setattr__ = <method-wrapper '__setattr__' of exceptions.ZeroDivisionError object>
        __setstate__ = <built-in method __setstate__ of exceptions.ZeroDivisionError object>
        __sizeof__ = <built-in method __sizeof__ of exceptions.ZeroDivisionError object>
        __str__ = <method-wrapper '__str__' of exceptions.ZeroDivisionError object>
        __subclasshook__ = <built-in method __subclasshook__ of type object>
        __unicode__ = <built-in method __unicode__ of exceptions.ZeroDivisionError object>
        args = ('integer division or modulo by zero',)
        message = 'integer division or modulo by zero'
    
    The above is a description of an error in a Python program.  Here is
    the original traceback:
    
    Traceback (most recent call last):
      File "/Users/a6/test_exception_process.py", line 81, in <module>
        func(1, 0)
      File "/Users/a6/test_exception_process.py", line 75, in func
        return a / b
    ZeroDivisionError: integer division or modulo by zero
    
    Process finished with exit code 1

完全不必再去log.debug(“a=%d” % a)了，个人感觉cgitb在线上环境不适合使用，适合在开发的过程中进行调试，非常的方便。   
也许你会问，cgitb为什么会这么屌？能获取这么详细的出错信息？其实它的工作原理同它的使用方式一样的简单，它只是覆盖了默认的sys.excepthook函数，sys.excepthook是一个默认的全局异常拦截器，可以尝试去自行对它修改：

def func(a, b):
        return a / b
    
    def my_exception_handler(exc_type, exc_value, exc_tb):
        print "i caught the exception:", exc_type
        while exc_tb:
            print "the line no:", exc_tb.tb_lineno
            print "the frame locals:", exc_tb.tb_frame.f_locals
            exc_tb = exc_tb.tb_next
    
    if __name__ == '__main__':
        import sys
        sys.excepthook = my_exception_handler
        func(1, 0)

输出：

i caught the exception: <type 'exceptions.ZeroDivisionError'>
    the line no: 99
    the frame locals: {'my_exception_handler': <function my_exception_handler at 0x1069800c8>, '__builtins__': <module '__builtin__' (built-in)>, '__file__': '/Users/a6/Downloads/PycharmProjects/speiyou_di_my/hive/shuangshi_haibian/test_exception_process.py', '__package__': None, 'sys': <module 'sys' (built-in)>, 'func': <function func at 0x10697ac08>, '__name__': '__main__', '__doc__': None}
    the line no: 87
    the frame locals: {'a': 1, 'b': 0}

**(4)使用logging模块来记录异常**  
在使用Java的时候，用log4j记录异常很简单，只要把Exception对象传递给log.error方法就可以了，但是在Python中就不行了，如果直接传递异常对象给log.error，那么只会在log里面出现一行异常对象的值。   
在Python中正确的记录Log方式应该是这样的：

logging.exception(ex)
    logging.error(ex, exc_info=1) # 指名输出栈踪迹, logging.exception的内部也是包了一层此做法
    logging.critical(ex, exc_info=1) # 更加严重的错误级别

具体示例如下:

import logging
    import os
    from datetime import datetime
    class LoggingInstance():
        def __init__(self):
            self.log_dir="logging.log"
        def make_log(self):
            # 初始化日志文件
            if not os.path.exists(self.log_dir):
                os.mkdir(self.log_dir)
            logging.basicConfig(level=logging.INFO,
                                filename="%s/log.%s" % (self.log_dir, datetime.now().strftime("%Y%m%d")), filemode='a',
                                format='%(asctime)s [%(levelname)s] [%(filename)s] [%(funcName)s] [%(lineno)d] %(message)s')
            logger = logging.getLogger(__name__)
            self.target_date = datetime.strptime(datetime.now().strftime("%Y%m%d"), "%Y%m%d")
            logger.info("init success, target_date=%s", self.target_date)
        def func(self, a, b):
            return a / b
    
    if __name__ == '__main__':
        obj_logging_instance=LoggingInstance()
        obj_logging_instance.make_log()
        import sys
        import traceback
        try:
            obj_logging_instance.func(1, 0)
        except Exception as ex:
            print "print using exc logging"
            logging.info("分割线 @@@@@@@ target_date=%s ",datetime.now())
            logging.exception(ex)  # 抛出异常方法一
            logging.info("分割线 @@@@@@@ target_date=%s ",datetime.now())
            logging.error(ex,exc_info=1)  # 抛出异常方法二
            logging.info("分割线 @@@@@@@ target_date=%s ",datetime.now())
            logging.warning(ex,exc_info=1)  # 抛出异常方法三
            logging.info("分割线 @@@@@@@ target_date=%s ",datetime.now())
            logging.fatal(ex,exc_info=1)    # 抛出异常方法四
            logging.info("分割线 @@@@@@@ target_date=%s ",datetime.now())
            #traceback.print_exc()  # 可以在输出窗口输出错误信息

输出日志文件logging.log文件内容如下：

2018-02-01 17:25:03,999 [INFO] [test_exception_process.py] [make_log] [156] init success, target_date=2018-02-01 00:00:00
    2018-02-01 17:25:03,999 [INFO] [test_exception_process.py] [<module>] [169] 分割线 @@@@@@@ target_date=2018-02-01 17:25:03.999508 
    2018-02-01 17:25:03,999 [ERROR] [test_exception_process.py] [<module>] [170] integer division or modulo by zero
    Traceback (most recent call last):
      File "/Users/a6/test_exception_process.py", line 166, in <module>
        obj_logging_instance.func(1, 0)
      File "/Users/a6/test_exception_process.py", line 158, in func
        return a / b
    ZeroDivisionError: integer division or modulo by zero
    2018-02-01 17:25:03,999 [INFO] [test_exception_process.py] [<module>] [171] 分割线 @@@@@@@ target_date=2018-02-01 17:25:03.999858 
    2018-02-01 17:25:03,999 [ERROR] [test_exception_process.py] [<module>] [172] integer division or modulo by zero
    Traceback (most recent call last):
      File "/Users/a6/test_exception_process.py", line 166, in <module>
        obj_logging_instance.func(1, 0)
      File "/Users/a6/test_exception_process.py", line 158, in func
        return a / b
    ZeroDivisionError: integer division or modulo by zero
    2018-02-01 17:25:04,000 [INFO] [test_exception_process.py] [<module>] [173] 分割线 @@@@@@@ target_date=2018-02-01 17:25:04.000040 
    2018-02-01 17:25:04,000 [WARNING] [test_exception_process.py] [<module>] [174] integer division or modulo by zero
    Traceback (most recent call last):
      File "/Users/a6/test_exception_process.py", line 166, in <module>
        obj_logging_instance.func(1, 0)
      File "/Users/a6test_exception_process.py", line 158, in func
        return a / b
    ZeroDivisionError: integer division or modulo by zero
    2018-02-01 17:25:04,000 [INFO] [test_exception_process.py] [<module>] [175] 分割线 @@@@@@@ target_date=2018-02-01 17:25:04.000206 
    2018-02-01 17:25:04,000 [CRITICAL] [test_exception_process.py] [<module>] [176] integer division or modulo by zero
    Traceback (most recent call last):
      File "/Users/a6/test_exception_process.py", line 166, in <module>
        obj_logging_instance.func(1, 0)
      File "/Users/a6/test_exception_process.py", line 158, in func
        return a / b
    ZeroDivisionError: integer division or modulo by zero
    2018-02-01 17:25:04,000 [INFO] [test_exception_process.py] [<module>] [177] 分割线 @@@@@@@ target_date=2018-02-01 17:25:04.000367

参考网址：http://blog.csdn.net/wbiblem/article/details/73432506