開個貼，用于記錄平時經常碰到的Python的錯誤同時對導致錯誤的原因進行分析，并持續更新，方便以后查詢，學習。

知識在于積累嘛！微笑

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

錯誤:

>>> 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)

【錯誤分析】不要誤以為元祖里有兩個參數，將元祖傳進去就可以了，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*,代表引用元祖

>>> f(*t)

'a', 'b'

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

錯誤:

>>> def func(y=2, x):

return x + y

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。

>>> def func(x, y=2):

return x + y

>>> func(1)

3

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

錯誤:

>>> D1 = {'x':1, 'y':2}

>>> D1['x']

1

>>> D1['z']

Traceback (most recent call last):

File "", line 1, in

D1['z']

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!'

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

錯誤:

>>> 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

【錯誤分析】exec語句最有用的地方在于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 ，其中就是起到放置代碼字符串命名空間的字典。

>>> from math import sqrt

>>> scope = {}

>>> exec "sqrt = 1" in scope

>>> sqrt(4)

2.0

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

錯誤:

>>> 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

【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:

>>> seq = ['1', '2', '3', '4']

>>> sep = '+'

>>> sep.join(seq)

'1+2+3+4'

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

錯誤:

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

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\

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

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

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!'

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

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

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...

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

>>> reload(sys)

Traceback (most recent call last):

File "", line 1, in

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)

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

>>> 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)

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

*args，才是將元祖中的每個元素作為參數

>>> 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

【錯誤分析】錯誤原因**匹配并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

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

【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]

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

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'

【錯誤分析】(1)的類型是整數，所以不能與另一個元祖做合并操作，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)

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

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

Traceback (most recent call last):

File "", line 1, in

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，元祖).

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}

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

>>> 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]

【錯誤分析】列表屬于可變對象,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，所以要實現反轉并排序，不能并行操作，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]

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

>>> 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

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

>>> 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'

【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。

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

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'

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

>>> [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

【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)]

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

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

count1.__secretCount

AttributeError: JustCounter instance has no attribute '__secretCount'

【錯誤分析】雙下劃線的類屬性__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

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

>>> print x

Traceback (most recent call last):

File "", line 1, in

NameError: name 'x' is not defined

>>> x = 1

>>> print x

1

【錯誤分析】Python不允許使用未賦值變量

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

>>> 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'

【錯誤分析】屬性錯誤,歸根到底在于元祖是不可變類型，所以沒有這幾種方法.

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

>>> 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

【錯誤分析】空元祖和空列表，沒有索引為0的項

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

>>> 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

【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 "", line 1, in

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()方法屬于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 "", line 1, in

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 "", 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 "", 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 "", 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'

【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 "", 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

【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...

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

>>> 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

【錯誤分析】元祖不可變，所以不可以更改;可以用切片或合并的方式達到目的.

>>> T = (1,2,3,4)

>>> (22,) + T[1:]

(22, 2, 3, 4)

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

>>> X = 1;

>>> Y = 2;

>>> X + = Y

File "", line 1

X + = Y

^

SyntaxError: invalid syntax

【錯誤分析】增強行賦值不能分開來寫，必須連著寫比如說 +=, *=

>>> X += Y

>>> X;Y

3

2

總結

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