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Python错误汇总
开个贴,用于记录平时经常碰到的Python的错误同时对导致错误的原因进行分析,并持续更新,方便以后查询,学习。
知识在于积累嘛!
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>>> hash(1,(2,[3,4])) Traceback (most recent call last): File "<pyshell#95>", line 1, in <module> hash((1,2,(2,[3,4]))) TypeError: unhashable type: 'list'【错误分析】字典中的键必须是不可变对象,如(整数,浮点数,字符串,元祖),可用hash()判断某个对象是否可哈希
>>> hash('string') -1542666171但列表中元素是可变对象,所以是不可哈希的,所以会报上面的错误.如果要用列表作为字典中的键,最简单的办法是:
>>> D = {} >>> D[tuple([3,4])] = 5 >>> D {(3, 4): 5}+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>> L = [2,1,4,3] >>> L.reverse().sort() Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'NoneType' object has no attribute 'sort' >>> L [3, 4, 1, 2]【错误分析】列表属于可变对象,其append(),sort(),reverse()会在原处修改对象,不会有返回值,或者说返回值为空,
所以要实现反转并排序,不能并行操作,要分开来写
>>> L = [2,1,4,3] >>> L.reverse() >>> L.sort() >>> L [1, 2, 3, 4]+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>> class = 78 SyntaxError: invalid syntax【错误分析】class是Python保留字,Python保留字不能做变量名,可以用Class,或klass
同样,保留字不能作为模块名来导入,比如说,有个and.py,但不能将其作为模块导入
>>> import and SyntaxError: invalid syntax+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>> f = open('D:\new\text.data','r') Traceback (most recent call last): File "<stdin>", line 1, in <module> IOError: [Errno 22] invalid mode ('r') or filename: 'D:\new\text.data' >>> f = open(r'D:\new\text.data','r') >>> f.read() 'Very\ngood\naaaaa'【错误分析】\n默认为换行,\t默认为TAB键,所以在D:\目录下找不到ew目录下的ext.data文件,将其改为raw方式输入即可。
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try: print 1 / 0 except ZeroDivisionError: print 'integer division or modulo by zero' finally: print 'Done' else: print 'Continue Handle other part' 报错如下: D:\>python Learn.py File "Learn.py", line 11 else: ^ SyntaxError: invalid syntax
【错误分析】错误原因,else, finally执行位置;正确的程序应该如下:
try: print 1 / 0 except ZeroDivisionError: print 'integer division or modulo by zero' else: print 'Continue Handle other part' finally: print 'Done'+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>> [x,y for x in range(2) for y in range(3)] File "<stdin>", line 1 [x,y for x in range(2) for y in range(3)] ^ SyntaxError: invalid syntax【错误分析】错误原因,列表解析中,x,y必须以数组的方式列出(x,y)
>>> [(x,y) for x in range(2) for y in range(3)] [(0, 0), (0, 1), (0, 2), (1, 0), (1, 1), (1, 2)]+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
class JustCounter: __secretCount = 0 def count(self): self.__secretCount += 1 print 'secretCount is:', self.__secretCount count1 = JustCounter() count1.count() count1.count() count1.__secretCount报错如下:
>>> secretCount is: 1 secretCount is: 2 Traceback (most recent call last): File "D:\Learn\Python\Learn.py", line 13, in <module> count1.__secretCount AttributeError: JustCounter instance has no attribute '__secretCount'
【错误分析】双下划线的类属性__secretCount不可访问,所以会报无此属性的错误.
解决办法如下:
# 1. 可以通过其内部成员方法访问 # 2. 也可以通过访问 ClassName._ClassName__Attr #或 ClassInstance._ClassName__Attr #来访问,比如: print count1._JustCounter__secretCount print JustCounter._JustCounter__secretCount+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>> print x Traceback (most recent call last): File "<stdin>", line 1, in <module> NameError: name 'x' is not defined >>> x = 1 >>> print x 1【错误分析】Python不允许使用未赋值变量
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>>> t = (1,2) >>> t.append(3) Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'tuple' object has no attribute 'append' >>> t.remove(2) Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'tuple' object has no attribute 'remove' >>> t.pop() Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'tuple' object has no attribute 'pop'【错误分析】属性错误,归根到底在于元祖是不可变类型,所以没有这几种方法.
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>>> t = () >>> t[0] Traceback (most recent call last): File "<stdin>", line 1, in <module> IndexError: tuple index out of range >>> l = [] >>> l[0] Traceback (most recent call last): File "<stdin>", line 1, in <module> IndexError: list index out of range【错误分析】空元祖和空列表,没有索引为0的项
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>>> if X>Y: ... X,Y = 3,4 ... print X,Y File "<stdin>", line 3 print X,Y ^ IndentationError: unexpected indent >>> t = (1,2,3,4) File "<stdin>", line 1 t = (1,2,3,4) ^ IndentationError: unexpected indent【错误分析】一般出在代码缩进的问题
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>>> f = file('1.txt') >>> f.readline() 'AAAAA\n' >>> f.readline() 'BBBBB\n' >>> f.next() 'CCCCC\n'【错误分析】如果文件里面没有行了会报这种异常
>>> f.next() # Traceback (most recent call last): File "<stdin>", line 1, in <module> StopIteration
有可迭代的对象的next方法,会前进到下一个结果,而在一系列结果的末尾时,会引发StopIteration的异常.
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>>> string = 'SPAM' >>> a,b,c = string Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: too many values to unpack【错误分析】接受的变量少了,应该是
>>> a,b,c,d = string >>> a,d ('S', 'M') #除非用切片的方式 >>> a,b,c = string[0],string[1],string[2:] >>> a,b,c ('S', 'P', 'AM') 或者 >>> a,b,c = list(string[:2]) + [string[2:]] >>> a,b,c ('S', 'P', 'AM') 或者 >>> (a,b),c = string[:2],string[2:] >>> a,b,c ('S', 'P', 'AM') 或者 >>> ((a,b),c) = ('SP','AM') >>> a,b,c ('S', 'P', 'AM') 简单点就是: >>> a,b = string[:2] >>> c = string[2:] >>> a,b,c ('S', 'P', 'AM')+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>> mydic={'a':1,'b':2} >>> mydic['a'] 1 >>> mydic['c'] Traceback (most recent call last): File "<stdin>", line 1, in ? KeyError: 'c'【错误分析】当映射到字典中的键不存在时候,就会触发此类异常, 或者可以,这样测试
>>> 'a' in mydic.keys() True >>> 'c' in mydic.keys() #用in做成员归属测试 False >>> D.get('c','"c" is not exist!') #用get或获取键,如不存在,会打印后面给出的错误信息 '"c" is not exist!'+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
File "study.py", line 3 return None ^ IndentationError: unexpected indent【错误分析】一般是代码缩进问题,TAB键或空格键不一致导致
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>>>def A(): return A() >>>A() #无限循环,等消耗掉所有内存资源后,报最大递归深度的错误 File "<pyshell#2>", line 2, in A return A()RuntimeError: maximum recursion depth exceeded class Bird: def __init__(self): self.hungry = True def eat(self): if self.hungry: print "Ahaha..." self.hungry = False else: print "No, Thanks!" 该类定义鸟的基本功能吃,吃饱了就不再吃 输出结果: >>> b = Bird() >>> b.eat() Ahaha... >>> b.eat() No, Thanks! 下面一个子类SingBird, class SingBird(Bird): def __init__(self): self.sound = 'squawk' def sing(self): print self.sound 输出结果: >>> s = SingBird() >>> s.sing() squawk SingBird是Bird的子类,但如果调用Bird类的eat()方法时, >>> s.eat() Traceback (most recent call last): File "<pyshell#5>", line 1, in <module> s.eat() File "D:\Learn\Python\Person.py", line 42, in eat if self.hungry: AttributeError: SingBird instance has no attribute 'hungry'【错误分析】代码错误很清晰,SingBird中初始化代码被重写,但没有任何初始化hungry的代码
class SingBird(Bird): def __init__(self): self.sound = 'squawk' self.hungry = Ture #加这么一句 def sing(self): print self.sound+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
class Bird: def __init__(self): self.hungry = True def eat(self): if self.hungry: print "Ahaha..." self.hungry = False else: print "No, Thanks!" class SingBird(Bird): def __init__(self): super(SingBird,self).__init__() self.sound = 'squawk' def sing(self): print self.sound >>> sb = SingBird() Traceback (most recent call last): File "<pyshell#5>", line 1, in <module> sb = SingBird() File "D:\Learn\Python\Person.py", line 51, in __init__ super(SingBird,self).__init__() TypeError: must be type, not classobj【错误分析】在模块首行里面加上__metaclass__=type,具体还没搞清楚为什么要加
__metaclass__=type class Bird: def __init__(self): self.hungry = True def eat(self): if self.hungry: print "Ahaha..." self.hungry = False else: print "No, Thanks!" class SingBird(Bird): def __init__(self): super(SingBird,self).__init__() self.sound = 'squawk' def sing(self): print self.sound >>> S = SingBird() >>> S. SyntaxError: invalid syntax >>> S. SyntaxError: invalid syntax >>> S.eat() Ahaha...+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>> T (1, 2, 3, 4) >>> T[0] = 22 Traceback (most recent call last): File "<pyshell#129>", line 1, in <module> T[0] = 22 TypeError: 'tuple' object does not support item assignment【错误分析】元祖不可变,所以不可以更改;可以用切片或合并的方式达到目的.
>>> T = (1,2,3,4) >>> (22,) + T[1:] (22, 2, 3, 4)+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Python错误汇总
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