下面是一个Table对象的代码,它有一个字段名属性。
class Table(object):
'''A CSV backed SQL table.'''
@property
def fieldnames(self):
with open(self.filename) as f:
return csv.DictReader(f).fieldnames
@property.setter
def fieldnames(self, fieldnames):
with open(self.filename, 'w') as f:
dr = csv.reader(f)
dw = csv.DictWriter(f, fieldnames=fieldnames)
dw.writerow(dict((field, field) for field in fieldnames))
for row in self:
dw.writerow(row)
当我尝试导入文件时,我得到错误:
seas486:PennAppSuite ceasarbautista$ python
Python 2.7.1 (r271:86832, Jun 25 2011, 05:09:01)
[GCC 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2335.15.00)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import table
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "table.py", line 7, in <module>
class Table(object):
File "table.py", line 9, in Table
@property.getter
TypeError: descriptor 'getter' requires a 'property' object but received a 'function'
谁能解释一下这个错误是什么意思?
我猜它相当于TypeError: unbound method ... must be called with ... instance as first argument (got ... instance instead)
。要通过装饰器向属性添加setter,你必须使用.setter
作为属性对象的成员/方法,而不是作为property
的静态方法/类方法。代码应该是这样的:
class Table(object):
'''A CSV backed SQL table.'''
@property
def fieldnames(self):
with open(self.filename) as f:
return csv.DictReader(f).fieldnames
@fieldnames.setter # <<<
def fieldnames(self, fieldnames):
with open(self.filename, 'w') as f:
dr = csv.reader(f)
dw = csv.DictWriter(f, fieldnames=fieldnames)
dw.writerow(dict((field, field) for field in fieldnames))
for row in self:
dw.writerow(row)