python基础6
- 2020 年 1 月 11 日
- 筆記
******************* * 异常处理与调式 * ******************* ***常见错误:*** 1) 名字没有定义,NameError In [1]: print a ————————————————————————— NameError Traceback (most recent call last) <ipython-input-1-9d7b17ad5387> in <module>() —-> 1 print a NameError: name 'a' is not defined 2) 分母为零,ZeroDivisionError In [2]: 10/0 ————————————————————————— ZeroDivisionError Traceback (most recent call last) <ipython-input-2-242277fd9e32> in <module>() —-> 1 10/0 ZeroDivisionError: integer division or modulo by zero 3) 文件不存在,IOError In [3]: open("westos") ————————————————————————— IOError Traceback (most recent call last) <ipython-input-3-2778d2991600> in <module>() —-> 1 open("westos") IOError: [Errno 2] No such file or directory: 'westos' 4) 语法错误,SyntaxError In [4]: for i in [1,2,3] File "<ipython-input-4-ae71676907af>", line 1 for i in [1,2,3] ^ SyntaxError: invalid syntax 5) 索引超出范围,IndexError In [5]: a = [1,2,3] In [6]: a[3] ————————————————————————— IndexError Traceback (most recent call last) <ipython-input-6-94e7916e7615> in <module>() —-> 1 a[3] IndexError: list index out of range In [7]: t =(1,2,3) In [8]: t[3] ————————————————————————— IndexError Traceback (most recent call last) <ipython-input-8-7d5cf04057c5> in <module>() —-> 1 t[3] IndexError: tuple index out of range In [9]: t[1:9] ###切片的时候,若超出范围,则默认为全部,不报错 Out[9]: (2, 3) ####python异常处理机制:try……except……finally###### 例: #!/usr/bin/env python #coding:utf-8 try: ###将可能发生错误的部分放在try下### print "staring……" li = [1,2,3] print a print li[3] except IndexError: ###捕获指定的异常### print 'index out of list length' except NameError: ###捕获指定的异常### print 'name is not define' finally: ###不管是否异常,一定会执行该代码块### print 'end……' 执行结果: staring…… name is not define end…… ###由结果可以看出,一旦捕获到异常就不会执行下面的语句,而是到了finally,如上例,捕获到NameError后,下一条语句就不再执行,因此,并没有去捕获IndexError,结果也只是输出NameError的打印内容和finally的打印内容##### ###当没有错误的时候可以加一条条件语句,显示没有错误#### #!/usr/bin/env python #coding:utf-8 try: print "staring……" li = [1,2,3] a = 1 print a print li[2] except IndexError: print 'index out of list length' except NameError: print 'name is not define' else: ####如果没有异常,则执行该代码块### print "No Error" finally: print 'end……' 执行结果: staring…… 1 3 No Error end…… ####可以将异常给变量,这样就可以自己打印错误#### #!/usr/bin/env python #coding:utf-8 try: print "staring……" li = [1,2,3] print a print li[2] except IndexError,e: ###将错误赋给e### print e ###会自动打印错误类型### except NameError,e: print e else: print "No Error" finally: print 'end……' 执行结果: staring…… name 'a' is not defined end…… ####在异常不知道的情况下,可以用BaseException,其实异常就是一个类,而BaseException是所有异常的父类#### #!/usr/bin/env python #coding:utf-8 try: print "staring……" li = [1,2,3] print li[3] print a except BaseException as e: print e except BaseException as e: print e else: print "No Error" finally: print 'end……' 执行结果: staring…… list index out of range end…… ####为了减少捕获异常的次数,可以将异常处理机制放在main函数下#### def func1(s): return func2(s)*2 def func2(s): return 10/s def main(): try: print func1("10") except TypeError,e: print e main() 执行结果: unsupported operand type(s) for /: 'int' and 'str' ####将错误信息写入文件### import logging ###导入logging模块### logging.basicConfig(filename='err.log') ###使用basicConfig方法### def func1(s): return func2(s)*2 def func2(s): return 10/s def main(): try: print func1("10") except Exception as e: logging.exception(e) ###将异常信息写入err.log文件### main() err.log文件的内容: ERROR:root:unsupported operand type(s) for /: 'int' and 'str' Traceback (most recent call last): File "/home/kiosk/PycharmProjects/pythonbasic/py5.1/error.py", line 48, in main print func1("10") File "/home/kiosk/PycharmProjects/pythonbasic/py5.1/error.py", line 43, in func1 return func2(s)*2 File "/home/kiosk/PycharmProjects/pythonbasic/py5.1/error.py", line 45, in func2 return 10/s TypeError: unsupported operand type(s) for /: 'int' and 'str' ####由此可见,以将错误的信息导入到了err.log文件### ####抛出异常和自定义异常### a = 1 ###抛出异常### if a == 1: raise NameError 执行结果: Traceback (most recent call last): File "/home/kiosk/PycharmProjects/pythonbasic/py5.1/error.py", line 57, in <module> raise NameError NameError class MyError(BaseException): ###自定义异常### pass a = 1 if a == 1: raise MyError 执行结果: charmProjects/pythonbasic/py5.1/error.py Traceback (most recent call last): File "/home/kiosk/PycharmProjects/pythonbasic/py5.1/error.py", line 60, in <module> raise MyError __main__.MyError 注意:一定不能够即捕获异常有抛出异常 #####调试-断言#### 断言失败: def foo(s): n = int(s) return 10 / n def main(): foo('0') assert foo(5) == 1 ###断言失败,assert 语句本身抛出AssertionError### print 'hello' 执行结果: Traceback (most recent call last): File "/home/kiosk/PycharmProjects/pythonbasic/py5.1/error.py", line 68, in <module> assert foo(5) == 1 AssertionError 断言成功: def foo(s): n = int(s) return 10 / n def main(): foo('0') assert foo(5) == 2 ###断言成功,就执行下面的语句### print 'hello' 执行结果: hello Python 解释器执行时可以用 -O 参数来关闭 assert,把所有的 assert 语句 当成 pass 例: [kiosk@foundation38 py5.1]$ python -O error.py hello ####将错误记录到文件里### import logging logging.basicConfig(filename='logging.log',level=logging.WARNING) ###level=logging.WARNING定义日志级别为WARNING def foo(s): n = int(s) logging.info('n=%d'% n) ###日志级别为info的内容### logging.warning('n=%d…warn' % n) return 10 / n def main(): foo('0') main() 执行后logging.log的内容为: WARNING:root:n=0…warn ###由此可见,并没有将日志级别为info的内容写入文件,因为,在最开始已经定义了级别为WARNING,除非级别比WARNING大的会记录到文件里### 例如:一开始定义日志级别为info import logging logging.basicConfig(filename='logging.log',level=logging.INFO) def foo(s): n = int(s) logging.info('n=%d'% n) logging.warning('n=%d…warn' % n) return 10 / n def main(): foo('0') main() 则执行后logging.log的内容为: INFO:root:n=0 WARNING:root:n=0…warn ###日志级别:debug,info,warning,error#### ###调试-pdb##### pdb让程序以单步方式运行,随时查看运行状态。n 可以单步执行代码,p 变量名 来查看变量,q 结束调试,退出程序 [kiosk@foundation38 py5.1]$ python -m pdb error.py > /home/kiosk/PycharmProjects/pythonbasic/py5.1/error.py(3)<module>() -> _author_ = "xiao" (Pdb) n > /home/kiosk/PycharmProjects/pythonbasic/py5.1/error.py(64)<module>() -> def foo(s): (Pdb) n > /home/kiosk/PycharmProjects/pythonbasic/py5.1/error.py(69)<module>() -> def main(): (Pdb) ####pdb.set_trace()#### import pdb n1 = 1 n = int(n1) print n pdb.set_trace() print 'world' pdb.set_trace() print 'hello' s = 2 print s 调试: 1 > /home/kiosk/PycharmProjects/pythonbasic/py5.1/error.py(81)<module>() -> print 'world' (Pdb) n world > /home/kiosk/PycharmProjects/pythonbasic/py5.1/error.py(82)<module>() -> pdb.set_trace() (Pdb) c ###继续### > /home/kiosk/PycharmProjects/pythonbasic/py5.1/error.py(83)<module>() -> print 'hello' (Pdb) c hello 2 ***************** * 正则表达式 * ***************** ###re.findall(p,text)### 将能匹配上的全返回,会返回一个 list In [13]: s = 'redhat linux hello world' In [14]: r = 'linux' In [15]: import re ###导入re模块### In [16]: re.findall(r,s) ###如果r在s里,则返回### Out[16]: ['linux'] In [17]: re.findall('red',s) Out[17]: ['red'] In [18]: re.findall('westos',s) ###如果不在,则返回空### Out[18]: [] In [1]: s = 'python linux hello wor\ld' In [2]: r = 'wor\l' In [3]: import re In [4]: re.findall(r,s) ###因为\是特殊字符,会认为是一个,所以会找不到### Out[4]: [] In [5]: r1 = r'wor\l' ###在前面加上r,就不会认为是特殊字符,就可以找到#### In [6]: re.findall(r1,s) Out[6]: ['wor\l'] In [7]: ####基本模式#### 1 字面模式: 就是字面长量,就代表其本身 2 . :匹配任何字符 3 d:匹配任何十进制数 4 D:匹配任何非数字字符 5 s:匹配任何空白字符 6 S:匹配任何非空间字符 7 w:匹配任何字母数字字符 8 W:匹配任何非字母数字自符 9 ^ 开头 $ 结尾 10 转义字符 ###次数的匹配### 次数的匹配 , 匹配其前面的字符出现的次数 : * 0 次或多次 + 一次或多次 ? 零次或一次 {n} 出现 n 次 {m,n} 出现 m 到 n 次 :{0,}相当于*,{1,}相当于+,{0,1}匹配一次或零次,相当于? 练习: 1 判断一个字符串是否是合法的 Email 的方法(要求以.com结尾的为合法的) In [16]: r = r'w+@w+.com' In [17]: import re In [18]: re.findall(r,'[email protected] [email protected]') Out[18]: ['[email protected]'] 2 判断满足029-1234567这样要求的电话号码的方法 In [19]: r = r'^d{3}-d{7}' In [20]: re.findall(r,'029-1234567 1234-1234567') Out[20]: ['029-1234567'] 3 判断变量是否合法 In [30]: r = r'^[_a-zA-Z]w*$' In [31]: re.findall(r,'_a-1') Out[31]: [] In [32]: re.findall(r,'a') Out[32]: ['a'] In [33]: re.findall(r,'a1') Out[33]: ['a1'] In [34]: re.findall(r,'_a1') Out[34]: ['_a1'] In [35]: re.findall(r,'1a1') Out[35]: [] ####编译re.compile()### 当我们在 Python 中使用正则表达式时,re 模块内部会干两件事情: 1. 编译正则表达式,如果正则表达式的字符串本身不合法,会报错; 2. 用编译后的正则表达式去匹配字符串。 重复使用几千次,出于效率的考虑,我们可以预编译该正则表达式。 In [36]: r = r't.p' In [37]: p = re.compile(r) In [38]: print p <_sre.SRE_Pattern object at 0x1f6a3c0> In [39]: re.findall(p,'top tap tab') Out[39]: ['top', 'tap'] ###re.match(p,text)### re.match(p,text) :p 为正则表达式模式, text 要查找的字符串,会返回一个match 对象 一定要用group()查看返回值 In [40]: re.match(p,'top tap tab') Out[40]: <_sre.SRE_Match at 0x23d0850> In [41]: a = re.match(p,'top tap tab') In [42]: a.group() ###显示匹配到的第一个字符,即在‘top tap tab’中查看第一个是否满足p的条件,满足则匹配成功返回,不满足则报错### Out[42]: 'top' In [43]: a.start() ###显示匹配的开始### Out[43]: 0 In [44]: a.end() ###显示匹配的结束### Out[44]: 3 In [46]: a.span() ###显示匹配的全部长度### Out[46]: (0, 3) ####当字符串中的第一项不满足匹配条件时,报错#### In [16]: a = re.match(p,'tab top tap') In [17]: a.group() ————————————————————————— AttributeError Traceback (most recent call last) <ipython-input-17-af218c045ead> in <module>() —-> 1 a.group() AttributeError: 'NoneType' object has no attribute 'group' ###一般用条件判断语句来描述是否匹配到,如果字符串的第一个字符是所匹配的,则打印找到匹配,如果不是,则打印没有匹配### In [54]: if a: ….: print 'Match found:%s'% a.group() ….: else: ….: print 'no match' ….: no match ###re.search(p,text)###### 只要在 text 中匹配到了 p 就返回,只返回第一个匹配到的,与re.match(p,text)的区别在与re.match(p,text)只在text的第一个查看是否匹配到p,而re.search(p,text)是在全部text中查找,只要text中有匹配到p的就返回 In [33]: p Out[33]: re.compile(r'hello') In [34]: re.search(p,'westos redhat hello linux') Out[34]: <_sre.SRE_Match at 0x2033f38> In [35]: a = re.search(p,'westos redhat hello linux') ###hello并不在第一个,但是仍然匹配到,并且返回了#### In [36]: a.group() Out[36]: 'hello' In [37]: 小练习:要求以.com或者.cn结尾的为合法的邮件,判断字符串是否为合法的邮件 In [32]: email = r'w+@w+(.com|.cn)' In [33]: a = re.search(email,'[email protected] [email protected]') In [34]: a.group() Out[34]: '[email protected]' ####re.finditer(p,text)#### 找到re匹配的所有子串,并把它们作为一个迭代器返回 In [1]: import re In [2]: a = re.fi re.findall re.finditer In [2]: a = re.finditer(r'hello', 'hello westos') In [3]: a.next().group() Out[3]: 'hello' ###re.sub(p,s,text)### 替换,将 p 匹配到的字符替换为 s In [4]: s = 'hello westos' In [6]: re.sub(r'wes..s','world','hello westos') ###第一个字符指被替换的字符,第二个字符指要替换成的字符,第三个字符指被替换的字符串### Out[6]: 'hello world' In [7]: re.subn(r'wes..s','world','hello westos') ###subn显示替换的次数### Out[7]: ('hello world', 1) In [8]: re.subn(r'wes..s','world','hello westos westos') Out[8]: ('hello world world', 2) ####re.split(p,text)### 按照 p 匹配,并且以匹配到的字符为分隔符切割 text, 返回一个切割后的 list In [10]: re.split(r'[+*]','123+34*18') ###以+和*作为分割,将'123+34*18'切割### Out[10]: ['123', '34', '18'] 小练习:从http://172.25.254.252下提取图片 #!/usr/bin/env python #coding:utf-8 import re import urllib,urllib2 def getHtml(url): try: page = urllib.urlopen(url) ###打开网址### html = page.read() ###读出网址的内容### except urllib2.URLError,e: print 'Download error…%s'% e return html def getImg(html): img_re = r'src="(.+.jpg)"' img_recom = re.compile(img_re) imglist = re.findall(img_recom,html) x = 1 for imgurl in imglist: urllib.urlretrieve(imgurl,"%s.png" %x) x += 1 html = getHtml('http://172.25.254.252/') getImg(html)