# 8.11 简化数据结构的初始化¶

## 解决方案¶

```import math

class Structure1:
# Class variable that specifies expected fields
_fields = []

def __init__(self, *args):
if len(args) != len(self._fields):
raise TypeError('Expected {} arguments'.format(len(self._fields)))
# Set the arguments
for name, value in zip(self._fields, args):
setattr(self, name, value)
```

```# Example class definitions
class Stock(Structure1):
_fields = ['name', 'shares', 'price']

class Point(Structure1):
_fields = ['x', 'y']

class Circle(Structure1):

def area(self):
return math.pi * self.radius ** 2
```

```>>> s = Stock('ACME', 50, 91.1)
>>> p = Point(2, 3)
>>> c = Circle(4.5)
>>> s2 = Stock('ACME', 50)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "structure.py", line 6, in __init__
raise TypeError('Expected {} arguments'.format(len(self._fields)))
TypeError: Expected 3 arguments
```

```class Structure2:
_fields = []

def __init__(self, *args, **kwargs):
if len(args) > len(self._fields):
raise TypeError('Expected {} arguments'.format(len(self._fields)))

# Set all of the positional arguments
for name, value in zip(self._fields, args):
setattr(self, name, value)

# Set the remaining keyword arguments
for name in self._fields[len(args):]:
setattr(self, name, kwargs.pop(name))

# Check for any remaining unknown arguments
if kwargs:
raise TypeError('Invalid argument(s): {}'.format(','.join(kwargs)))
# Example use
if __name__ == '__main__':
class Stock(Structure2):
_fields = ['name', 'shares', 'price']

s1 = Stock('ACME', 50, 91.1)
s2 = Stock('ACME', 50, price=91.1)
s3 = Stock('ACME', shares=50, price=91.1)
# s3 = Stock('ACME', shares=50, price=91.1, aa=1)
```

```class Structure3:
# Class variable that specifies expected fields
_fields = []

def __init__(self, *args, **kwargs):
if len(args) != len(self._fields):
raise TypeError('Expected {} arguments'.format(len(self._fields)))

# Set the arguments
for name, value in zip(self._fields, args):
setattr(self, name, value)

# Set the additional arguments (if any)
extra_args = kwargs.keys() - self._fields
for name in extra_args:
setattr(self, name, kwargs.pop(name))

if kwargs:
raise TypeError('Duplicate values for {}'.format(','.join(kwargs)))

# Example use
if __name__ == '__main__':
class Stock(Structure3):
_fields = ['name', 'shares', 'price']

s1 = Stock('ACME', 50, 91.1)
s2 = Stock('ACME', 50, 91.1, date='8/2/2012')
```

## 讨论¶

```class Structure:
# Class variable that specifies expected fields
_fields= []
def __init__(self, *args):
if len(args) != len(self._fields):
raise TypeError('Expected {} arguments'.format(len(self._fields)))

# Set the arguments (alternate)
self.__dict__.update(zip(self._fields,args))
```

```>>> help(Stock)
Help on class Stock in module __main__:
class Stock(Structure)
...
| Methods inherited from Structure:
|
| __init__(self, *args, **kwargs)
|
...
>>>
```