本部分练习python中的异常处理，相当于Java中的try…catch…finally，不同的是：
1.Python中的语句是try….except….finally 2.Python中有try….except…else…finally语句，期中else语句是当没有异常捕获时执行； 3.Python中主动抛出异常的语句时raise。
# 1.try except 捕获error
import logging
try:
print('try...')
r = 10 / 2
print('result:', r)
except ZeroDivisionError as e:
print('except:', e)
else:
print("No error")
finally:
print('finally...')
print('END')
try:
print('try...')
r = 10 / 0
print('result:', r)
except ZeroDivisionError as e:
print('except:', e)
# logging.exception(e)
logging.exception("Logging Error")
else:
print("No error")
finally:
print('finally...')
print('END')
class myError(BaseException):
pass
try:
raise myError()
except myError as e:
logging.exception(e)
# raise
# 练习 根据异常堆栈定位错误，并修改语句
from functools import reduce
def str2num(s):
# int(s) 根据堆栈修改
return float(s)
def calc(exp):
ss = exp.split('+')
ns = map(str2num, ss)
return reduce(lambda acc, x: acc + x, ns)
def main():
r = calc('100 + 200 + 345')
print('100 + 200 + 345 =', r)
r = calc('99 + 88 + 7.6')
print('99 + 88 + 7.6 =', r)
main()
上述代码中，最后的练习部分，异常堆栈输出为：
Traceback (most recent call last):
File "C:\Users\lihongzhe\PycharmProjects\pyforwork\demo\errorHandling.py", line 63, in <module>
main()
File "C:\Users\lihongzhe\PycharmProjects\pyforwork\demo\errorHandling.py", line 59, in main
r = calc('99 + 88 + 7.6')
File "C:\Users\lihongzhe\PycharmProjects\pyforwork\demo\errorHandling.py", line 53, in calc
return reduce(lambda acc, x: acc + x, ns)
File "C:\Users\lihongzhe\PycharmProjects\pyforwork\demo\errorHandling.py", line 47, in str2num
return int(s)
ValueError: invalid literal for int() with base 10: ' 7.6'
可以看到，错误是因为用int()函数对非整数进行了强转，因此改为float()即可。改后输出如下：
100 + 200 + 345 = 645.0
99 + 88 + 7.6 = 194.6
