错误:
【错误分析】第二个参数必须为类,否则会报TypeError,所以正确的应该是这样的:
但如果第二个参数是类型对象,则不会报上面的错误,是允许的,比如说:
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
错误:
【错误分析】这个涉及到调用顺序问题,即解析方法的MRO调用顺序,在Python2.7版本之后,这样调用会报错,
必须是子类先放前面,然后才是父类.如下所示,方不会报错.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
错误:
【错误分析】foo()未带参数self,也未带cls参数,属于类的静态方法,类的静态方法调用,实例不能直接调用,需要再声明一个静态方法
或者通过@staticmethod来调用
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
错误:
【错误分析】__dict__是实例的特殊属性,但在内建属性中,不存在__dict__属性,一般的情况是:
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
错误:
【错误分析】如果定义了构造器,它不应当返回任何对象,因为实例对象是自动在实例化调用后返回的。相应地,__init__()就不应当返回任何对象(应当为None);否则就可能出现冲突,因为只能返回实例。试着返回非None的任何其他对象都会导致TypeError异常
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
错误:
- >>> def f(x, y):
- print x, y
- >>> t = (‘a‘, ‘b‘)
- >>> f(t)
- Traceback (most recent call last):
- File "<pyshell#65>", line 1, in <module>
- f(t)
- TypeError: f() takes exactly 2 arguments (1 given)
【错误分析】不要误以为元祖里有两个参数,将元祖传进去就可以了,实际上元祖作为一个整体只是一个参数,
实际需要两个参数,所以报错。必需再传一个参数方可.
- >>> f(t, ‘var2‘)
- (‘a‘, ‘b‘) var2
更常用的用法: 在前面加*,代表引用元祖
- >>> f(*t)
- ‘a‘, ‘b‘
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
错误:
- >>> def func(y=2, x):
- return x + y
- SyntaxError: non-default argument follows default argument
【错误分析】在C++,Python中默认参数从左往右防止,而不是相反。这可能跟参数进栈顺序有关。
- >>> def func(x, y=2):
- return x + y
- >>> func(1)
- 3
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
错误:
- >>> D1 = {‘x‘:1, ‘y‘:2}
- >>> D1[‘x‘]
- 1
- >>> D1[‘z‘]
- Traceback (most recent call last):
- File "<pyshell#185>", line 1, in <module>
- D1[‘z‘]
- KeyError: ‘z‘
【错误分析】这是Python中字典键错误的提示,如果想让程序继续运行,可以用字典中的get方法,如果键存在,则获取该键对应的值,不存在的,返回None,也可打印提示信息.
- >>> D1.get(‘z‘, ‘Key Not Exist!‘)
- ‘Key Not Exist!‘
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
错误:
- >>> from math import sqrt
- >>> exec "sqrt = 1"
- >>> sqrt(4)
- Traceback (most recent call last):
- File "<pyshell#22>", line 1, in <module>
- sqrt(4)
- TypeError: ‘int‘ object is not callable
【错误分析】exec语句最有用的地方在于动态地创建代码字符串,但里面存在的潜在的风险,它会执行其他地方的字符串,在CGI中更是如此!比如例子中的sqrt = 1,从而改变了当前的命名空间,从math模块中导入的sqrt不再和函数名绑定而是成为了一个整数。要避免这种情况,可以通过增加in <scope>,其中<scope>就是起到放置代码字符串命名空间的字典。
- >>> from math import sqrt
- >>> scope = {}
- >>> exec "sqrt = 1" in scope
- >>> sqrt(4)
- 2.0
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
错误:
- >>> seq = [1, 2, 3, 4]
- >>> sep = ‘+‘
- >>> sep.join(seq)
- Traceback (most recent call last):
- File "<pyshell#25>", line 1, in <module>
- sep.join(seq)
- TypeError: sequence item 0: expected string, int found
【错误分析】join是split的逆方法,是非常重要的字符串方法,但不能用来连接整数型列表,所以需要改成:
- >>> seq = [‘1‘, ‘2‘, ‘3‘, ‘4‘]
- >>> sep = ‘+‘
- >>> sep.join(seq)
- ‘1+2+3+4‘
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
错误:
- >>> print r‘C:\Program Files\foo\bar\‘
- SyntaxError: EOL while scanning string literal
【错误分析】Python中原始字符串以r开头,里面可以放置任意原始字符,包括\,包含在字符中的\不做转义。
但是,不能放在末尾!也就是说,最后一个字符不能是\,如果真 需要的话,可以这样写:
- >>> print r‘C:\Program Files\foo\bar‘ "\\"
- C:\Program Files\foo\bar\
- >>> print r‘C:\Program Files\foo\bar‘ + "\\"
- C:\Program Files\foo\bar\
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
代码:
- bad = ‘bad‘
- try:
- raise bad
- except bad:
- print ‘Got Bad!‘
错误:
- >>>
- Traceback (most recent call last):
- File "D:\Learn\Python\Learn.py", line 4, in <module>
- raise bad
- TypeError: exceptions must be old-style classes or derived from BaseException, not str
【错误分析】因所用的Python版本2.7,比较高的版本,raise触发的异常,只能是自定义类异常,而不能是字符串。所以会报错,字符串改为自定义类,就可以了。
- class Bad(Exception):
- pass
- def raiseException():
- raise Bad()
- try:
- raiseException()
- except Bad:
- print ‘Got Bad!‘
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- class Super:
- def method(self):
- print "Super‘s method"
- class Sub(Super):
- def method(self):
- print "Sub‘s method"
- Super.method()
- print "Over..."
- S = Sub()
- S.method()
执行上面一段代码,错误如下:
- >>>
- Sub‘s method
- Traceback (most recent call last):
- File "D:\Learn\Python\test.py", line 12, in <module>
- S.method()
- File "D:\Learn\Python\test.py", line 8, in method
- Super.method()
- TypeError: unbound method method() must be called with Super instance as first argument (got nothing instead)
【错误分析】Python中调用类的方法,必须与实例绑定,或者调用自身.
ClassName.method(x, ‘Parm‘)
ClassName.method(self)
所以上面代码,要调用Super类的话,只需要加个self参数即可。
- class Super:
- def method(self):
- print "Super‘s method"
- class Sub(Super):
- def method(self):
- print "Sub‘s method"
- Super.method(self)
- print "Over..."
- S = Sub()
- S.method()
- #输出结果
- >>>
- Sub‘s method
- Super‘s method
- Over...
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- >>> reload(sys)
- Traceback (most recent call last):
- File "<stdin>", line 1, in <module>
- NameError: name ‘sys‘ is not defined
【错误分析】reload期望得到的是对象,所以该模块必须成功导入。在没导入模块前,不能重载.
- >>> import sys
- >>> reload(sys)
- <module ‘sys‘ (built-in)>
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- >>> def f(x, y, z):
- return x + y + z
- >>> args = (1,2,3)
- >>> print f(args)
- Traceback (most recent call last):
- File "<pyshell#6>", line 1, in <module>
- print f(args)
- TypeError: f() takes exactly 3 arguments (1 given)
【错误分析】args是一个元祖,如果是f(args),那么元祖是作为一个整体作为一个参数
*args,才是将元祖中的每个元素作为参数
- >>> f(*args)
- 6
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- >>> def f(a,b,c,d):
- ... print a,b,c,d
- ...
- >>> args = (1,2,3,4)
- >>> f(**args)
- Traceback (most recent call last):
- File "<stdin>", line 1, in <module>
- TypeError: f() argument after ** must be a mapping, not tuple
【错误分析】错误原因**匹配并收集在字典中所有包含位置的参数,但传递进去的却是个元祖。
所以修改传递参数如下:
- >>> args = {‘a‘:1,‘b‘:2,‘c‘:3}
- >>> args[‘d‘] = 4
- >>> f(**args)
- 1 2 3 4
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
【错误分析】在函数hider()内使用了内置变量open,但根据Python作用域规则LEGB的优先级:
先是查找本地变量==》模块内的其他函数==》全局变量==》内置变量,查到了即停止查找。
所以open在这里只是个字符串,不能作为打开文件来使用,所以报错,更改变量名即可。
可以导入__builtin__模块看到所有内置变量:异常错误、和内置方法
>>> import __builtin__
>>> dir(__builtin__)
[‘ArithmeticError‘, ‘AssertionError‘, ‘AttributeError‘,..
.........................................zip,filter,map]
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- In [105]: T1 = (1)
- In [106]: T2 = (2,3)
- In [107]: T1 + T2
- ---------------------------------------------------------------------------
- TypeError Traceback (most recent call last)
- <ipython-input-107-b105c7b32d90> in <module>()
- ----> 1 T1 + T2;
- TypeError: unsupported operand type(s) for +: ‘int‘ and ‘tuple‘
【错误分析】(1)的类型是整数,所以不能与另一个元祖做合并操作,如果只有一个元素的元祖,应该用(1,)来表示
- In [108]: type(T1)
- Out[108]: int
- In [109]: T1 = (1,)
- In [110]: T2 = (2,3)
- In [111]: T1 + T2
- Out[111]: (1, 2, 3)
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- >>> 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]
或者用下面的方法实现:
- In [103]: sorted(reversed([2,1,4,3]))
- Out[103]: [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。
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- 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
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- >>> 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.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- >>> 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
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- >>> 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
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- >>> 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.
next()方法属于Python的魔法方法,这种方法的效果就是:逐行读取文本文件的最佳方式就是根本不要去读取。
取而代之的用for循环去遍历文件,自动调用next()去调用每一行,且不会报错
- for line in open(‘test.txt‘,‘r‘):
- print line
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- >>> 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
- ^
- dentationError: 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
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- >>>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)
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
- >>> X = 1;
- >>> Y = 2;
- >>> X + = Y
- File "<stdin>", line 1
- X + = Y
- ^
- SyntaxError: invalid syntax
【错误分析】增强行赋值不能分开来写,必须连着写比如说 +=, *=
- >>> X += Y
- >>> X;Y
- 3
- 2
原文地址:https://www.cnblogs.com/wzbk/p/8410805.html