11 . Python3之异常,调试和测试

# 语法错误示范一
if

# 语法错误示范二
def test:
    pass

# 语法错误示范三
class Foo
    pass

# 语法错误示范四
print(haha)

#TypeError:int类型不可迭代
for i in 3:
    pass
#ValueError
num=input(">>: ") #输入hello
int(num)

#NameError
aaa

#IndexError
l=['egon','aa']
l[3]

#KeyError
dic={'name':'egon'}
dic['age']

#AttributeError
class Foo:pass
Foo.x

#ZeroDivisionError:无法完成计算
res1=1/0
res2=1+'str'

# 异常三部分信息:
	1. 追踪信息
	2. 类型
	3. 值

异常处理结构:
try:
	# 会出现异常的代码块
except  异常类型 as 异常别名:
	# 异常处理逻辑
else:
	# 没有出现异常执行该分支
finally:
	# 无论是否出现异常都会执行该分支

# 主动抛出异常
raise  异常类型('异常信息')

# 自定义异常类
class MyError(BaseException):
    def  __init__(self,msg):
	self.msg = msg

# 断言:
# assert  断言条件

AGE = 10
while True:
    age=input('>>: ').strip()
    if age.isdigit(): # 只有在age为字符串形式的整数时，下列代码才不会出错,该条件是可预知的
        age=int(age)    
        if age == AGE:
            print('you get it')
            break

# 基本语法为:
try:
    被检测的代码块
except 异常类型:
    try中一旦检测到异常，就执行这个位置的逻辑
# Example1
try:
    f=open('a.txt')
    g=(line.strip() for line in f)
    print(next(g))
    print(next(g))
    print(next(g))
except StopIteration:
    f.close()

s1 = 'hello'
try:
    int(s1)
except IndexError as e: # 未捕获到异常，程序直接报错
    print e

s1 = 'hello'
try:
    int(s1)
except IndexError as e:
    print(e)
except KeyError as e:
    print(e)
except ValueError as e:
    print(e)

s1 = 'hello'
try:
    int(s1)
except Exception as e:
    print(e)

s1 = 'hello'
try:
    int(s1)
except IndexError as e:
    print(e)
except KeyError as e:
    print(e)
except ValueError as e:
    print(e)
except Exception as e:
    print(e)

s1 = 'hello'
try:
    int(s1)
except IndexError as a:
    print(e)
except KeyError as e:
    print(e)
except ValueError as e:
    print(e)
# except Exception as e:
#     print(e)
else:
    print('try内代码块没有异常则执行我')
finally:
    print('无论异常与否，都会执行该模块，通常是进行')

try:
    raise TypeError('类型错误')
except Exception as e:
    print(e)

class EgonException(BaseException):
    def __init__(self,msg):
        self.msg=msg
    def __str__(self):
        return self.msg

try:
    raise EgonException('类型错误')
except EgonException as e:
    va1 = traceback.format_exc()  # 获取到堆栈信息
    print(e)
    print(va1)

assert 1 == 1
assert 1 == 2

# 把错误处理和真正的工作分开来
# 代码更易组织，更清晰，复杂的工作任务更容易实现
# 毫无疑问，更安全了，不至于由于一些小的疏忽而使程序意外崩溃了.

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')

# 虽然程序会出错，但程序打印完错误信息后会继续执行，并正常退出.
# 通过配置,logging还可以把错误记录到日志文件里，方便事后排查.