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)
>>> f(t, 'var2') ('a', 'b') var2
>>> f(*t) 'a', 'b'
>>> def func(y=2, x): return x + y SyntaxError: non-default argument follows default argument
>>> 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 "<pyshell#185>", line 1, in <module> D1['z'] KeyError: 'z'
>>> 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 "<pyshell#22>", line 1, in <module> sqrt(4) TypeError: 'int' object is not callable
>>> from math import sqrt >>> scope = {} >>> exec "sqrt = 1" in scope >>> sqrt(4) 2.0
>>> 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'
错误:
>>> print r'C:\Program Files\foo\bar\' SyntaxError: EOL while scanning string literal
>>> print r'C:\Program Files\foo\bar' "\\" C:\Program Files\foo\bar\ >>> print r'C:\Program Files\foo\bar' + "\\" C:\Program Files\foo\bar\
bad = 'bad' try: raise bad except bad: print 'Got Bad!'
>>> 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
【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 <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)
【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)
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
>>> import sys >>> reload(sys) <module 'sys' (built-in)>
>>> 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
【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) <ipython-input-107-b105c7b32d90> in <module>() ----> 1 T1 + T2; TypeError: unsupported operand type(s) for +: 'int' and 'tuple'
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 "<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
>>> D = {} >>> D[tuple([3,4])] = 5 >>> D {(3, 4): 5}
>>> 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]
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
>>> 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'
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
>>> [(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 <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
>>> 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'
>>> 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() '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 "<stdin>", line 1, in <module> StopIteration
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
>>> 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'
>>> '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 ^ dentationError: unexpected indent
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>>>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!"
>>> b = Bird() >>> b.eat() Ahaha... >>> b.eat() No, Thanks!
class SingBird(Bird): def __init__(self): self.sound = 'squawk' def sing(self): print self.sound
>>> 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:\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
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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
__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
>>> 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
>>> X += Y >>> X;Y 3 2