Python常見的錯誤匯總

Python常見的錯誤匯總

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錯誤：

TypeError: 'NoneType' object is not callable

【錯誤分析】我是在別的文件中寫了一個函數，然后在python console調用使用該函數，出現了上述錯誤。原因是因為沒有對別的文件中函數進行編譯，只要打開該調用函數的文件，然后點擊運行，之后再在python console中調用使用該函數就不會報錯。

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錯誤:

【錯誤分析】第二個參數必須為類，否則會報TypeError，所以正確的應該是這樣的:

但如果第二個參數是類型對象，則不會報上面的錯誤，是允許的，比如說:

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錯誤:

【錯誤分析】這個涉及到調用順序問題，即解析方法的MRO調用順序，在Python2.7版本之后，這樣調用會報錯，

必須是子類先放前面，然后才是父類.如下所示，方不會報錯.

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錯誤:

【錯誤分析】foo()未帶參數self,也未帶cls參數,屬於類的靜態方法，類的靜態方法調用，實例不能直接調用，需要再聲明一個靜態方法

或者通過@staticmethod來調用

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錯誤:

【錯誤分析】__dict__是實例的特殊屬性，但在內建屬性中，不存在__dict__屬性，一般的情況是:

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錯誤:

【錯誤分析】如果定義了構造器，它不應當返回任何對象，因為實例對象是自動在實例化調用后返回的。相應地，__init__()就不應當返回任何對象(應當為None);否則就可能出現沖突，因為只能返回實例。試着返回非None的任何其他對象都會導致TypeError異常

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錯誤:

 

1 >>> def f(x, y):  
2     print x, y  
3 >>> t = ('a', 'b')  
4 >>> f(t)  
5   
6 Traceback (most recent call last):  
7   File "<pyshell#65>", line 1, in <module>  
8     f(t)  
9 TypeError: f() takes exactly 2 arguments (1 given)

 

 

 

【錯誤分析】不要誤以為元組里有兩個參數，將元組傳進去就可以了，實際上元祖作為一個整體只是一個參數，

實際需要兩個參數，所以報錯。必需再傳一個參數方可.

>>> f(t, 'var2')  
('a', 'b') var2  

更常用的用法: 在前面加*,代表引用元組 

>>> f(*t)  
'a', 'b'  

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錯誤:

 

1 >>> def func(y=2, x):  
2     return x + y  
3 SyntaxError: non-default argument follows default argument 

 

 

 

【錯誤分析】在C++,Python中默認參數從左往右防止，而不是相反。這可能跟參數進棧順序有關。

1 >>> def func(x, y=2):  
2     return x + y  
3 >>> func(1)  
4 3 

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錯誤:

 

1 >>> D1 = {'x':1, 'y':2}  
2 >>> D1['x']  
3 1  
4 >>> D1['z']  
5   
6 Traceback (most recent call last):  
7   File "<pyshell#185>", line 1, in <module>  
8     D1['z']  
9 KeyError: 'z' 

 

【錯誤分析】這是Python中字典鍵錯誤的提示，如果想讓程序繼續運行，可以用字典中的get方法，如果鍵存在，則獲取該鍵對應的值，不存在的，返回None,也可打印提示信息.

>>> D1.get('z', 'Key Not Exist!')  
'Key Not Exist!' 

 

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錯誤:

>>> 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  

【錯誤分析】exec語句最有用的地方在於動態地創建代碼字符串，但里面存在的潛在的風險，它會執行其他地方的字符串，在CGI中更是如此！比如例子中的sqrt = 1，從而改變了當前的命名空間，從math模塊中導入的sqrt不再和函數名綁定而是成為了一個整數。要避免這種情況，可以通過增加in <scope>，其中<scope>就是起到放置代碼字符串命名空間的字典。

1 >>> from math import sqrt  
2 >>> scope = {}  
3 >>> exec "sqrt = 1" in scope  
4 >>> sqrt(4)  
5 2.0 

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錯誤:

>>> 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  

【錯誤分析】join是split的逆方法，是非常重要的字符串方法，但不能用來連接整數型列表，所以需要改成:

1 >>> seq = ['1', '2', '3', '4']  
2 >>> sep = '+'  
3 >>> sep.join(seq)  
4 '1+2+3+4' 

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錯誤:

 

1 >>> print r'C:\Program Files\foo\bar\'  
2 SyntaxError: EOL while scanning string literal  

 

【錯誤分析】Python中原始字符串以r開頭，里面可以放置任意原始字符，包括\，包含在字符中的\不做轉義。

但是，不能放在末尾！也就是說，最后一個字符不能是\，如果真 需要的話，可以這樣寫:

>>> print r'C:\Program Files\foo\bar' "\\"  
C:\Program Files\foo\bar\  
>>> print r'C:\Program Files\foo\bar' + "\\"  
C:\Program Files\foo\bar\   

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代碼:

bad = 'bad'  
  
try:  
    raise bad  
except bad:  
    print 'Got Bad!' 

錯誤:

>>>   
  
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 

【錯誤分析】因所用的Python版本2.7,比較高的版本，raise觸發的異常，只能是自定義類異常，而不能是字符串。所以會報錯，字符串改為自定義類，就可以了。

class Bad(Exception):  
    pass  
  
def raiseException():  
    raise Bad()  
  
try:  
    raiseException()  
except Bad:  
    print 'Got Bad!' 

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 錯誤：

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() 

執行上面一段代碼，錯誤如下:

>>>   
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)  

【錯誤分析】Python中調用類的方法，必須與實例綁定，或者調用自身.

ClassName.method(x, 'Parm')

ClassName.method(self)

所以上面代碼，要調用Super類的話，只需要加個self參數即可。

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()  
  
  
#輸出結果  
>>>   
Sub's method  
Super's method  
Over... 

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錯誤：

>>> reload(sys)  
Traceback (most recent call last):  
  File "<stdin>", line 1, in <module>  
NameError: name 'sys' is not defined  

【錯誤分析】reload期望得到的是對象，所以該模塊必須成功導入。在沒導入模塊前，不能重載.

>>> import sys  
>>> reload(sys)  
<module 'sys' (built-in)>  

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 錯誤 

>>> 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)  

【錯誤分析】args是一個元組，如果是f(args)，那么元組是作為一個整體作為一個參數，

*args，才是將元組中的每個元素作為參數

>>> f(*args)  
6 

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  錯誤：

>>> 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 

【錯誤分析】錯誤原因**匹配並收集在字典中所有包含位置的參數，但傳遞進去的卻是個元祖。

所以修改傳遞參數如下:

>>> args = {'a':1,'b':2,'c':3}  
>>> args['d'] = 4  
>>> f(**args)  
1 2 3 4 

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【錯誤分析】在函數hider()內使用了內置變量open，但根據Python作用域規則LEGB的優先級:

先是查找本地變量==》模塊內的其他函數==》全局變量==》內置變量，查到了即停止查找。

所以open在這里只是個字符串，不能作為打開文件來使用，所以報錯，更改變量名即可。

可以導入__builtin__模塊看到所有內置變量：異常錯誤、和內置方法

 import __builtin__
>>> dir(__builtin__)
['ArithmeticError', 'AssertionError', 'AttributeError',...
  ........................................zip,filter,map]

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 錯誤：

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'  

【錯誤分析】(1)的類型是整數，所以不能與另一個元祖做合並操作，如果只有一個元素的元祖，應該用(1,)來表示

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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 錯誤：

>>> 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'  

【錯誤分析】字典中的鍵必須是不可變對象，如(整數，浮點數，字符串，元組).

可用hash()判斷某個對象是否可哈希

>>> hash('string')  
-1542666171

但列表中元素是可變對象，所以是不可哈希的，所以會報上面的錯誤.

如果要用列表作為字典中的鍵，最簡單的辦法是:

>>> D = {}  
>>> D[tuple([3,4])] = 5  
>>> D  
{(3, 4): 5}  

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錯誤：

>>> 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]  

【錯誤分析】列表屬於可變對象,其append(),sort(),reverse()會在原處修改對象，不會有返回值，

或者說返回值為空，所以要實現反轉並排序，不能並行操作，要分開來寫。

>>> L = [2,1,4,3]  
>>> L.reverse()  
>>> L.sort()  
>>> L  
[1, 2, 3, 4] 

或者用下面的方法實現:

In [103]: sorted(reversed([2,1,4,3]))  
Out[103]: [1, 2, 3, 4]  

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 錯誤：

>>> class = 78  
SyntaxError: invalid syntax  

【錯誤分析】class是Python保留字，Python保留字不能做變量名，可以用Class，或klass
同樣，保留字不能作為模塊名來導入，比如說，有個and.py，但不能將其作為模塊導入

>>> import and  
SyntaxError: invalid syntax  

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錯誤：

>>> 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'  

【錯誤分析】\n默認為換行，\t默認為TAB鍵.

所以在D:\目錄下找不到ew目錄下的ext.data文件，將其改為raw方式輸入即可。

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錯誤：

try:  
    print 1 / 0  
      
except ZeroDivisionError:  
    print 'integer division or modulo by zero'  
      
finally:  
    print 'Done'  
  
else:    
    print 'Continue Handle other part'  
報錯如下:  
D:\>python Learn.py  
  File "Learn.py", line 11  
    else:  
       ^  
SyntaxError: invalid syntax  

【錯誤分析】錯誤原因，else, finally執行位置;正確的程序應該如下:

try:  
    print 1 / 0  
      
except ZeroDivisionError:  
    print 'integer division or modulo by zero'  
  
  
else:    
    print 'Continue Handle other part'  
      
finally:  
    print 'Done' 

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錯誤： 

>>> [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  

【錯誤分析】錯誤原因，列表解析中，x,y必須以數組的方式列出(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)]  

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class JustCounter:  
    __secretCount = 0  
  
    def count(self):  
        self.__secretCount += 1  
        print 'secretCount is:', self.__secretCount  
  
count1 = JustCounter()  
  
count1.count()  
count1.count()  
  
count1.__secretCount  

報錯如下:

>>>   
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'  

【錯誤分析】雙下划線的類屬性__secretCount不可訪問，所以會報無此屬性的錯誤. 

解決辦法如下:

# 1. 可以通過其內部成員方法訪問  
# 2. 也可以通過訪問  
ClassName._ClassName__Attr  
#或   
ClassInstance._ClassName__Attr  
#來訪問，比如：  
print count1._JustCounter__secretCount  
print JustCounter._JustCounter__secretCount  

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

>>> 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'  

【錯誤分析】屬性錯誤,歸根到底在於元組是不可變類型，所以沒有這幾種方法.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

>>> 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

【錯誤分析】空元組和空列表，沒有索引為0的項
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

>>> 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

【錯誤分析】一般出在代碼縮進的問題
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

>>> f = file('1.txt')  
>>> f.readline()  
'AAAAA\n'  
>>> f.readline()  
'BBBBB\n'  
>>> f.next()  
'CCCCC\n'

【錯誤分析】如果文件里面沒有行了會報這種異常

>>> f.next() #  
Traceback (most recent call last):  
  File "<stdin>", line 1, in <module>  
StopIteration  

有可迭代的對象的next方法,會前進到下一個結果,而在一系列結果的末尾時,會引發StopIteration的異常.

next()方法屬於Python的魔法方法，這種方法的效果就是:逐行讀取文本文件的最佳方式就是根本不要去讀取。

取而代之的用for循環去遍歷文件，自動調用next()去調用每一行，且不會報錯

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  

【錯誤分析】接受的變量少了，應該是

>>> 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')  
  
簡單點就是:  
>>> 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'  

【錯誤分析】當映射到字典中的鍵不存在時候，就會觸發此類異常, 或者可以，這樣測試

>>> 'a' in mydic.keys()  
True  
>>> 'c' in mydic.keys()              #用in做成員歸屬測試  
False  
>>> D.get('c','"c" is not exist!')   #用get或獲取鍵，如不存在，會打印后面給出的錯誤信息  
'"c" is not exist!'  

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

File "study.py", line 3  
  return None  
  ^  
dentationError: unexpected indent  

【錯誤分析】一般是代碼縮進問題，TAB鍵或空格鍵不一致導致

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

>>>def A():  
return A()  
>>>A() #無限循環，等消耗掉所有內存資源后，報最大遞歸深度的錯誤    
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!"  
該類定義鳥的基本功能吃，吃飽了就不再吃  
輸出結果:  
>>> b = Bird()  
>>> b.eat()  
Ahaha...  
>>> b.eat()  
No, Thanks!  
下面一個子類SingBird,  
class SingBird(Bird):  
    def __init__(self):  
        self.sound = 'squawk'  
    def sing(self):  
        print self.sound  
輸出結果:  
>>> s = SingBird()  
>>> s.sing()  
squawk  
SingBird是Bird的子類，但如果調用Bird類的eat()方法時,  
>>> 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' 

【錯誤分析】代碼錯誤很清晰,SingBird中初始化代碼被重寫，但沒有任何初始化hungry的代碼

class SingBird(Bird):  
    def __init__(self):  
        self.sound = 'squawk'  
        self.hungry = Ture #加這么一句  
    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  

【錯誤分析】在模塊首行里面加上__metaclass__=type，具體還沒搞清楚為什么要加

__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... 

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

【錯誤】

 

1 >>> T  
2 (1, 2, 3, 4)  
3 >>> T[0] = 22   
4 Traceback (most recent call last):  
5   File "<pyshell#129>", line 1, in <module>  
6     T[0] = 22  
7 TypeError: 'tuple' object does not support item assignment  

 

 

>>> 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  

【錯誤分析】元組不可變，所以不可以更改;可以用切片或合並的方式達到目的.

>>> 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  

【錯誤分析】增強行賦值不能分開來寫，必須連着寫比如說 +=, *=

>>> X += Y  
>>> X;Y  
3  
2

 參考：http://blog.csdn.net/jerry_1126/article/details/39395899