Python从门到精通(二):包装-02-异常处理和日志

相比java，python的异常和java中不同，python主要是防止程序异常被中止。一旦被catch后它还行往下执行。

一、异常

1.1、忽略

pass这个关键字相当于一个占位符，好比TODO是一样的，只表示此行什么也不做，不代表其它的行代码不执行；

try:
print(5/0)
except ZeroDivisionError:
pass
print("ddd") #这行还是可以正常执行的

1.2、捕获

def parse_int(s):
try:
n = int(v)
except Exception as e:
print('Could not parse, Reason:', e)

parse_int('30') ##Reason: name 'v' is not defined

1.3、异常链

try:
client_obj.get_url(url)
except (URLError, ValueError, SocketTimeout):
client_obj.remove_url(url)try:
client_obj.get_url(url)
except (URLError, ValueError):
client_obj.remove_url(url)
except SocketTimeout:
client_obj.handle_url_timeout(url)try:
f = open(filename)
except OSError:
pass

1.4、自定义

class NetworkError(Exception):
pass

class HostnameError(NetworkError):
pass


class CustomError(Exception):
def __init__(self, message, status):
super().__init__(message, status)
self.message = message
self.status = statustry:
msg = s.recv()
except TimeoutError as e:
print(e)
except RuntimeError as e:
print(e.args)

1.5、抛出

try:
raise RuntimeError('It failed') #抛出新异常-raise Error
except RuntimeError as e:
print(e.args)def example():
try:
int('N/A')
except ValueError:
print("Didn't work")
raise #捕获后再抛出

二、异常的显示方式

2.1、打印信息

try:
print(5/0)
except ZeroDivisionError as e:
print(e.args)

2.2、控制台警告

import warnings
warnings.simplefilter('always')
def func(x, y, log_file=None, debug=False):
if log_file is not None:
warnings.warn('log_file argument deprecated', DeprecationWarning)

func(1, 2, 'a')

#第一行日志输出warn内容，第二行输出代码内容
/Users/liudong/personCode/python/pythonTest/app/base/base_type.py:5: UserWarning: log_file argument deprecated
warnings.warn('log_file argument deprecated')

2.2、存储文件

import json;

numbers = [2,3,4,5,6];
fileName = "numbers.json";

with open(fileName, "w") as fileObj:
json.dump(numbers, fileObj);

with open(fileName, "r") as fileObj:
number1 = json.load(fileObj);

三、日志

需要用到logging库。

3.1、硬编码日志

默认会输出到当前文件夹下。

import logging

def main():
# Configure the logging system
logging.basicConfig(
filename='app.log',
level=logging.ERROR
# level = logging.WARNING,
# format = f'%(levelname)s:%(asctime)s:%(message)s'
)

host_name = 'www.python.org'
item = 'spam'
file_name = 'data.csv'
mode = 'r'

logging.critical(f'Host {host_name} unknown')
logging.error(f"Couldn't find {item}")
logging.warning('Feature is deprecated')
logging.info(f'Opening file {file_name}, mode={mode}')
logging.debug('Got here')

if __name__ == '__main__':
main()CRITICAL:root:Host www.python.org unknown
ERROR:root:Couldn't find 'spam'

CRITICAL:2020-06-03 08:21:28,334:Host www.python.org unknown
ERROR:2020-06-03 08:21:28,335:Couldn't find spam
WARNING:2020-06-03 08:21:28,335:Feature is deprecated

CRITICAL:root:Host www.python.org unknown
ERROR:root:Couldn't find spam

3.2、采用配置文件来配置日志配置

logging.basicConfig(
config_call()
)

def config_call():
import logging.config
logging.config.fileConfig('log_config.ini')[loggers]
keys=root

[handlers]
keys=defaultHandler

[formatters]
keys=defaultFormatter

[logger_root]
level=INFO
handlers=defaultHandler
qualname=root

[handler_defaultHandler]
class=FileHandler
formatter=defaultFormatter
args=('app.log', 'a')

[formatter_defaultFormatter]
format=%(levelname)s:%(name)s:%(message)s

3.3、自定义工具类

import logging

log = logging.getLogger(__name__)
log.addHandler(logging.NullHandler())

def func():
log.critical('A Critical Error!')
log.debug('A debug message')

#以下是三种不同的实现方式
logging.basicConfig()
func()

logging.basicConfig(level=logging.ERROR)
func()

#创建模块
logging.getLogger('log_func').level=logging.DEBUG
func()