我有一个简单的类,它延长了接受带有值修饰符的字符串(即’10m’将是1024 * 1024 * 10)
我有__str__函数打印传入的原始值(即如果’10m’传入,返回’10m’)
问题是当我打电话时,例如：
>>> printf("%d" % Size('10m'))
我得到以下内容
SystemError: ../Objects/stringobject.c:4044: bad argument to internal function
显然,如果我打印“％s”,我会得到’10米’
所以问题是,因为我是子类化long,为什么类应该在获取long值时调用__str__.
顺便说一下,多一点测试显示％x和％f将打印整数值,这让我更加困惑.我也尝试添加__format__,但似乎只在调用“…”.format()时调用.
编辑#1,这是代码：
class Size(long):
'''Represents a size reflected bytes. Subclass of long.
Size passed in must be in the formats terabytes
'''
units = { 'b':1,'s':512,'k':1024,'m':1024 ** 2,'g':1024 ** 3,'t':1024 ** 4 }
def __new__(cls,value):
'''Creates a Size object with the specified value.
Value can be a number or a string (optionally prefixed with '0x' or
postfixed with a type character). If using hex,the final character
will be treated as part of the value if it is a hex digit,regardless
of whether it is a valid unit character.
Examples:
Size(50)
Size("0x100s") # 256 sectors
Size("64")
Size("512k")
Size("0x1b") # this is 1b bytes,not 1 byte
'''
self = _new_unit_number(value,cls.units,long,cls)
return self
def __init__(self,value):
self._orig_value = value
def __str__(self):
print "calling str"
return str(self._orig_value) # Convert to str in case the object was created w/an int
def __format__(self,format_spec):
print "calling format"
print format_spec
try:
value = format(str(self),format_spec)
except ValueError:
value = format(int(self),format_spec)
return value
def _new_unit_number(value,unit_list,num_type,cls):
'''Converts a string of numbers followed by a unit character to the
requested numeric type (int or long for example).
'''
base = 10
start = 0
digits = string.digits
try:
if value[0:2] == '0x':
start = 2
base = 16
digits = string.hexdigits
if value[-1] in digits:
return num_type.__new__(cls,value[start:],base)
else:
try:
# Use a regex to split the parts of the unit
regex_string = '(\d+[%s])' % (''.join(unit_list.keys()))
parts = [x for x in re.split(regex_string,value[start:]) if x]
if len(parts) == 1:
return num_type.__new__(cls,num_type(value[start:-1],base) * unit_list[value[-1]])
else:
# Total up each part
# There's probably a better way to do this.
# This converts each unit to its base type,stores it in total,# only to be converted back to the base type.
total = 0
for part in parts:
total += num_type(part[start:-1],base) * unit_list[part[-1]]
# Finally return the requested unit
return num_type.__new__(cls,total)
except KeyError:
raise ValueError("Invalid %s unit identifier: %s"
% (cls.__name__,unit_list[value[-1]]))
# not a string or empty,see if we can still use the class's constructor
except (TypeError,IndexError):
return num_type.__new__(cls,value)
最佳答案
不是答案,但评论太久了.
我发现这个问题非常有趣.我尝试使用以下方法复制行为：
#! /usr/bin/python2.7
class Size (long):
def __new__ (cls,arg):
if arg and type (arg) == str:
if arg [-1] == 'm':
return super (Size,cls).__new__ (cls,long (arg [:-1] ) * 2 ** 20)
return super (Size,arg)
def __init__ (self,arg):
self.s = arg
def __str__ (self):
return self.s
a = Size ('12m')
print (a)
print ('%s' % a)
#The following fails horribly
print ('%d' % a)
OP描述的行为.但现在有趣的是：当我从int继承而不是从long继承时,它运行顺利：
class Size (int):
def __new__ (cls,int (arg [:-1] ) * 2 ** 20)
return super (Size,arg):
self.s = arg
def __str__ (self):
return self.s
也就是说,它在python2中工作正常,但在python3中失败.奇怪,奇怪.
