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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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 "", line 1, in 
    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 "", line 1, in 
    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 "", line 1, in 
    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 ，其中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 "", line 1, in 
    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 
    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 
    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 "", line 1, in 
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)

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

>>> def f(x, y, z):
	return x + y + z

>>> args = (1,2,3)
>>> print f(args)

Traceback (most recent call last):
  File "", line 1, in 
    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 "", line 1, in 
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)
 in ()
----> 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)

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>>> hash(1,(2,[3,4]))

Traceback (most recent call last):
  File "", line 1, in 
    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 "", line 1, in 
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

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>>> f = open('D:\new\text.data','r')
Traceback (most recent call last):
  File "", line 1, in 
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 "", 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 
    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 "", line 1, in 
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 "", line 1, in 
AttributeError: 'tuple' object has no attribute 'append'
>>> t.remove(2)
Traceback (most recent call last):
  File "", line 1, in 
AttributeError: 'tuple' object has no attribute 'remove'
>>> t.pop()
Traceback (most recent call last):
  File "", line 1, in 
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 "", line 1, in 
IndexError: tuple index out of range
>>> l = []
>>> l[0]
Traceback (most recent call last):
  File "", line 1, in 
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 "", line 3
    print X,Y
    ^
IndentationError: unexpected indent


>>>   t = (1,2,3,4)
  File "", 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 "", line 1, in 
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 "", line 1, in 
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 "", 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

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

>>>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 "", 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 "", line 1, in 
    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 "", line 1, in 
    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 "", line 1, in 
    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 "", 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