python编程中遇到的错误和解决方法集锦
June 16, 2015
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:
>>> 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
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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!'
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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
>>> from math import sqrt
>>> scope = {}
>>> exec "sqrt = 1" in scope
>>> sqrt(4)
2.0
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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'
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错误:
>>> print r'C:Program Filesfoobar' 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 Filesfoobar' "\" C:Program Filesfoobar >>> print r'C:Program Filesfoobar' + "\" C:Program Filesfoobar
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代码:
bad = 'bad'
try:
raise bad
except bad:
print 'Got Bad!'
错误:
>>>
Traceback (most recent call last):
File "D:LearnPythonLearn.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!'
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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:LearnPythontest.py", line 12, in <module>
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)
【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...
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>>> 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)>
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>>> 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
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>>> 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
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【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]
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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)
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>>> 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}
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>>> 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]
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>>> 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:newtext.data','r')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IOError: [Errno 22] invalid mode ('r') or filename: 'D:newtext.data'
>>> f = open(r'D:newtext.data','r')
>>> f.read()
'Veryngoodnaaaaa'
【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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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)]
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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
报错如下:
>>>
secretCount is: 1
secretCount is: 2
Traceback (most recent call last):
File "D:LearnPythonLearn.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
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>>> 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
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>>> 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
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>>> 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
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>>> f = file('1.txt')
>>> f.readline()
'AAAAAn'
>>> f.readline()
'BBBBBn'
>>> f.next()
'CCCCCn'
【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
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>>> 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!'
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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:LearnPythonPerson.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:LearnPythonPerson.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
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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