Python程序设计-清华大学出版社-董付国第8章 异常处理结构与程序调试

1、 10 * (1/0)Traceback (most recent call last): File , line 1, in ?ZeroDivisionError: division by zero 4 + spam*3Traceback (most recent call last): File , line 1, in ?NameError: name spam is not defined 2 + 2Traceback (most recent call last): File , line 1, in ?TypeError: Cant convert int object to st

2、r implicitlyl语法错误和逻辑错误不属于异常，但有些语法错误往往会导致异常，例如由于大小写拼写错误而访问不存在的对象。l当Python检测到一个错误时，解释器就会指出当前流已无法继续执行下去，这时候就出现了异常。异常是指因为程序出错而在正常控制流以外采取的行为。l异常分为两个阶段：第一个阶段是引起异常发生的错误；第二个阶段是检测并处理阶段。可以继承Python内置异常类来实现自定义的异常类。class ShortInputException(Exception):你定义的异常类。def _init_(self, length, atleast):Exception._init_(se

3、lf)self.length = lengthself.atleast = atleast try:s = raw_input(请输入 - )if len(s) class MyError(Exception): def _init_(self, value): self.value = value def _str_(self): return repr(self.value) try: raise MyError(2*2) except MyError as e: print(My exception occurred, value:, e.value)My exception occur

4、red, value: 4 raise MyError(oops!)Traceback (most recent call last): File , line 1, in ?_main_.MyError: oops!try.except.结构try子句中的代码块放置可能出现异常的语句，except子句中的代码块处理异常。try:try块#被监控的语句except Exception, reason:except块#处理异常的语句 while True: try: x = int(input(Please enter a number: ) break except ValueError: p

5、rint(That was no valid number. Try again.)try.except.else.语句如果try范围内捕获了异常，就执行except块；如果try范围内没有捕获异常，就执行else块。a_list = China, America, England, Franceprint 请输入字符串的序号while True:n = input( )try:print a_listnexcept IndexError:print 列表元素的下标越界，请重新输入字符串的序号else: breakfor arg in sys.argv1: try: f = open(arg,

6、 r) except IOError: print(cannot open, arg) else: print(arg, has, len(f.readlines(), lines) f.close()import systry: f = open(myfile.txt) s = f.readline() i = int(s.strip()except OSError as err: print(OS error: 0.format(err)except ValueError: print(Could not convert data to an integer.)except: print(

7、Unexpected error:, sys.exc_info()0) raisel将要捕获的异常写在一个元组中，可以使用一个excep语句捕获多个异常：import systry: f = open(myfile.txt) s = f.readline() i = int(s.strip()except (OSError, ValueError,RuntimeError, NameError): pass def divide(x, y): try: result = x / y except ZeroDivisionError: print(division by zero!) else:

8、 print(result is, result) finally: print(executing finally clause) divide(2, 1)result is 2.0executing finally clause divide(2, 0)division by zero!executing finally clause divide(2, 1)executing finally clauseTraceback (most recent call last): File , line 1, in ? File , line 3, in divideTypeError: uns

9、upported operand type(s) for /: str and strlPython2with open(d:test.txt) as f: for line in f:print linelPython3with open(myfile.txt) as f: for line in f: print(line, end=)import sys try: 1/0 except: tuple = sys.exc_info()print tuple完整/简写命令用法示例解释a(rgs) 显示当前函数中的参数b(reak) filename:lineno | function, condition b 173在173行设置断点b function在function函数第一条可执行语句位置设置断点b不带参数则列出所有断点，包括每个断点的触发次数、当前忽略计数、以及与之关联的条件b 175, condition设置条件断点，仅当condition的值为True时该断点有效cl(ear) filename:lineno | bpnumber bpnumber . cl清除所有断点cl filename:lineno删除指定文件指定行的所有断点cl 3 5 9删除第3、5、9个断点condition bpnu