Python程序設(shè)計-清華大學(xué)出版社-董付國第8章 異常處理結(jié)構(gòu)與程序調(diào)試

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語法錯誤和邏輯錯誤不屬于異常，但有些語法錯誤往往會導(dǎo)致異常，例如由于大小寫拼寫錯誤而訪問不存在的對象。l當(dāng)Python檢測到一個錯誤時，解釋器就會指出當(dāng)前流已無法繼續(xù)執(zhí)行下去，這時候就出現(xiàn)了異常。異常是指因為程序出錯而在正?？刂屏饕酝獠扇〉男袨?。l異常分為兩個階段：第一個階段是引起異常發(fā)生的錯誤；第二個階段是檢測并處理階段?？梢岳^承Python內(nèi)置異常類來實現(xiàn)自定義的異常類。class ShortInputException(Exception):你定義的異常類。def _init_(self, length, atleast):Exception._init_(se

3、lf)self.length = lengthself.atleast = atleast try:s = raw_input(請輸入 - )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.結(jié)構(gòu)try子句中的代碼塊放置可能出現(xiàn)異常的語句，except子句中的代碼塊處理異常。try:try塊#被監(jiān)控的語句except Exception, reason:except塊#處理異常的語句 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.語句如果try范圍內(nèi)捕獲了異常，就執(zhí)行except塊；如果try范圍內(nèi)沒有捕獲異常，就執(zhí)行else塊。a_list = China, America, England, Franceprint 請輸入字符串的序號while True:n = input( )try:print a_listnexcept IndexError:print 列表元素的下標(biāo)越界，請重新輸入字符串的序號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將要捕獲的異常寫在一個元組中，可以使用一個excep語句捕獲多個異常：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/簡寫命令用法示例解釋a(rgs) 顯示當(dāng)前函數(shù)中的參數(shù)b(reak) filename:lineno | function, condition b 173在173行設(shè)置斷點(diǎn)b function在function函數(shù)第一條可執(zhí)行語句位置設(shè)置斷點(diǎn)b不帶參數(shù)則列出所有斷點(diǎn)，包括每個斷點(diǎn)的觸發(fā)次數(shù)、當(dāng)前忽略計數(shù)、以及與之關(guān)聯(lián)的條件b 175, condition設(shè)置條件斷點(diǎn)，僅當(dāng)condition的值為True時該斷點(diǎn)有效cl(ear) filename:lineno | bpnumber bpnumber . cl清除所有斷點(diǎn)cl filename:lineno刪除指定文件指定行的所有斷點(diǎn)cl 3 5 9刪除第3、5、9個斷點(diǎn)condition bpnu