python编程中遇到的错误和解决方法集锦

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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!微笑

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错误:

[cc lang=”python”]

>>> 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)

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【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.

[cc lang=”python”]

>>> f(t, ‘var2’)

(‘a’, ‘b’) var2

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更常用的用法: 在前面加*,代表引用元祖

[cc lang=”python”]

>>> f(*t)

‘a’, ‘b’

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错误:

[cc lang=”python”]

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

return x + y

SyntaxError: non-default argument follows default argument

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【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。

[cc lang=”python”]

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

return x + y

>>> func(1)

3

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错误:

[cc lang=”python”]

>>> D1 = {‘x’:1, ‘y’:2}

>>> D1[‘x’]

1

>>> D1[‘z’]

Traceback (most recent call last):

File ““, line 1, in

D1[‘z’]

KeyError: ‘z’

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【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.

[cc lang=”python”]

>>> D1.get(‘z’, ‘Key Not Exist!’)

‘Key Not Exist!’

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错误:

[cc lang=”python”]

>>> 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

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【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。

[cc lang=”python”]

>>> from math import sqrt

>>> scope = {}

>>> exec “sqrt = 1″ in scope

>>> sqrt(4)

2.0

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错误:

[cc lang=”python”]

>>> 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

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【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:

[cc lang=”python”]

>>> seq = [‘1’, ‘2’, ‘3’, ‘4’]

>>> sep = ‘+’

>>> sep.join(seq)

‘1+2+3+4’

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错误:

[cc lang=”python”]

>>> print r’C:Program Filesfoobar’

SyntaxError: EOL while scanning string literal

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【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:

[cc lang=”python”]

>>> print r’C:Program Filesfoobar’ “\”

C:Program Filesfoobar

>>> print r’C:Program Filesfoobar’ + “\”

C:Program Filesfoobar

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代码:

[cc lang=”python”]

bad = ‘bad’

try:

raise bad

except bad:

print ‘Got Bad!’

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错误:

[cc lang=”python”]

>>>

Traceback (most recent call last):

File “D:LearnPythonLearn.py”, line 4, in

raise bad

TypeError: exceptions must be old-style classes or derived from BaseException, not str

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【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。

[cc lang=”python”]

class Bad(Exception):

pass

def raiseException():

raise Bad()

try:

raiseException()

except Bad:

print ‘Got Bad!’

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[cc lang=”python”]

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()

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执行上面一段代码,错误如下:

[cc lang=”python”]

>>>

Sub’s method

Traceback (most recent call last):

File “D:LearnPythontest.py”, line 12, in

S.method()

File “D:LearnPythontest.py”, line 8, in method

Super.method()

TypeError: unbound method method() must be called with Super instance as first argument (got nothing instead)

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【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.

[cc lang=”python”]

ClassName.method(x, ‘Parm’)

ClassName.method(self)

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所以上面代码,要调用Super类的话,只需要加个self参数即可。

[cc lang=”python”]

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…

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[cc lang=”python”]

>>> reload(sys)

Traceback (most recent call last):

File ““, line 1, in

NameError: name ‘sys’ is not defined

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【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.

[cc lang=”python”]

>>> import sys

>>> reload(sys)

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[cc lang=”python”]

>>> 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)

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【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

[cc lang=”python”]

>>> f(*args)

6

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[cc lang=”python”]

>>> 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

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【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:

[cc lang=”python”]

>>> args = {‘a’:1,’b’:2,’c’:3}

>>> args[‘d’] = 4

>>> f(**args)

1 2 3 4

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

python编程中遇到的错误和解决方法集锦

python编程中遇到的错误和解决方法集锦

【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

[cc lang=”python”]

>>> import __builtin__

>>> dir(__builtin__)

[‘ArithmeticError’, ‘AssertionError’, ‘AttributeError’,..

…………………………………..zip,filter,map]

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[cc lang=”python”]

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’

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【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

[cc lang=”python”]

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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[cc lang=”python”]

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

Traceback (most recent call last):

File ““, line 1, in

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

TypeError: unhashable type: ‘list’

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【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

[cc lang=”python”]

>>> hash(‘string’)

-1542666171

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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:

[cc lang=”python”]

>>> D = {}

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

>>> D

{(3, 4): 5}

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[cc lang=”python”]

>>> 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]

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【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

[cc lang=”python”]

>>> L = [2,1,4,3]

>>> L.reverse()

>>> L.sort()

>>> L

[1, 2, 3, 4]

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或者用下面的方法实现:

[cc lang=”python”]

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

Out[103]: [1, 2, 3, 4]

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[cc lang=”python”]

>>> class = 78

SyntaxError: invalid syntax

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【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

[cc lang=”python”]

>>> import and

SyntaxError: invalid syntax

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[cc lang=”python”]

>>> f = open(‘D:newtext.data’,’r’)

Traceback (most recent call last):

File ““, line 1, in

IOError: [Errno 22] invalid mode (‘r’) or filename: ‘D:newtext.data’

>>> f = open(r’D:newtext.data’,’r’)

>>> f.read()

‘Veryngoodnaaaaa’

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【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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[cc lang=”python”]

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

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【错误分析】错误原因,else, finally执行位置;正确的程序应该如下:

[cc lang=”python”]

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

[cc lang=”python”]

>>> [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

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【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)

[cc lang=”python”]

>>> [(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

[/cc]

报错如下:

[cc lang=”python”]

>>>

secretCount is: 1

secretCount is: 2

Traceback (most recent call last):

File “D:LearnPythonLearn.py”, line 13, in

count1.__secretCount

AttributeError: JustCounter instance has no attribute ‘__secretCount’

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【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:

[cc lang=”python”]

# 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

[/cc]

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[cc lang=”python”]

>>> print x

Traceback (most recent call last):

File ““, line 1, in

NameError: name ‘x’ is not defined

>>> x = 1

>>> print x

1

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【错误分析】Python不允许使用未赋值变量

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[cc lang=”python”]

>>> 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’

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【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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[cc lang=”python”]

>>> 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

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【错误分析】空元祖和空列表,没有索引为0的项

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[cc lang=”python”]

>>> 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

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【错误分析】一般出在代码缩进的问题

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[cc lang=”python”]

>>> f = file(‘1.txt’)

>>> f.readline()

‘AAAAAn’

>>> f.readline()

‘BBBBBn’

>>> f.next()

‘CCCCCn’

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【错误分析】如果文件里面没有行了会报这种异常

[cc lang=”python”]

>>> f.next() #

Traceback (most recent call last):

File ““, line 1, in

StopIteration

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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

[cc lang=”python”]

for line in open(‘test.txt’,’r’):

print line

[/cc]

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[cc lang=”python”]

>>> string = ‘SPAM’

>>> a,b,c = string

Traceback (most recent call last):

File ““, line 1, in

ValueError: too many values to unpack

[/cc]

【错误分析】接受的变量少了,应该是

[cc lang=”python”]

>>> 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’)

[/cc]

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

[cc lang=”python”]

>>> mydic={‘a’:1,’b’:2}

>>> mydic[‘a’]

1

>>> mydic[‘c’]

Traceback (most recent call last):

File ““, line 1, in ?

KeyError: ‘c’

[/cc]

【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

[cc lang=”python”]

>>> ‘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!’

[/cc]

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

[cc lang=”python”]

File “study.py”, line 3

return None

^

dentationError: unexpected indent

[/cc]

【错误分析】一般是代码缩进问题,TAB键或空格键不一致导致

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

[cc lang=”python”]

>>>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!”

[/cc]

该类定义鸟的基本功能吃,吃饱了就不再吃

输出结果:

[cc lang=”python”]

>>> b = Bird()

>>> b.eat()

Ahaha…

>>> b.eat()

No, Thanks!

[/cc]

下面一个子类SingBird,

[cc lang=”python”]

class SingBird(Bird):

def __init__(self):

self.sound = ‘squawk’

def sing(self):

print self.sound

[/cc]

输出结果:

[cc lang=”python”]

>>> s = SingBird()

>>> s.sing()

squawk

[/cc]

SingBird是Bird的子类,但如果调用Bird类的eat()方法时,

[cc lang=”python”]

>>> s.eat()

Traceback (most recent call last):

File ““, line 1, in

s.eat()

File “D:LearnPythonPerson.py”, line 42, in eat

if self.hungry:

AttributeError: SingBird instance has no attribute ‘hungry’

[/cc]

【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

[cc lang=”python”]

class SingBird(Bird):

def __init__(self):

self.sound = ‘squawk’

self.hungry = Ture #加这么一句

def sing(self):

print self.sound

[/cc]

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

[cc lang=”python”]

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:LearnPythonPerson.py”, line 51, in __init__

super(SingBird,self).__init__()

TypeError: must be type, not classobj

[/cc]

【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

[cc lang=”python”]

__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…

[/cc]

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

[cc lang=”python”]

>>> 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

[/cc]

【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.

[cc lang=”python”]

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

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

(22, 2, 3, 4)

[/cc]

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

[cc lang=”python”]

>>> X = 1;

>>> Y = 2;

>>> X + = Y

File ““, line 1

X + = Y

^

SyntaxError: invalid syntax

[/cc]

【错误分析】增强行赋值不能分开来写,必须连着写比如说 +=, *=

[cc lang=”python”]

>>> X += Y

>>> X;Y

3

2

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python编程中遇到的错误和解决方法就是这样,欢迎大家参考。。。。

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