[英]Property set correctly inside an object but not accessible outside
I'm working under python pyramid, with Python3. 我正在使用Python3在python pyramid下工作。
I have a model that looks like this: 我有一个看起来像这样的模型:
class OneTimeCode(Base):
__tablename__ = 'otc_one_time_codes'
otc_one_time_code_id = Column(Integer, primary_key=True)
otc_one_time_code = Column(String(32))
otc_usr_user_id = Column(Integer, ForeignKey('usr_users.usr_user_id'), nullable=True)
otc_expire_time = Column(DateTime)
def __init__(self, otc_usr_user_id, otc_expire_time=None):
self.otc_usr_user_id = otc_usr_user_id
if otc_expire_time is None:
self.otc_expire_time = (datetime.now() + timedelta(6*365/12)).isoformat()
else:
self.otc_expire_time = otc_expire_time
@classmethod
def get_code(self, hlength=6):
seed = datetime.now() + timedelta(random.randrange(1,10000))
tmp_hash = hashlib.md5(seed.strftime("%Y-%m-%d %H:%M:%S.%F").encode('utf-8')).hexdigest()
if hlength == 32:
self.otc_one_time_code = tmp_hash
else:
self.otc_one_time_code = tmp_hash[0 : hlength]
print(self.otc_one_time_code)
The problem is, when I instantiate one of these objects and then explicitly call get_code, the print line at the end prints to the screen the code successfully. 问题是,当我实例化这些对象之一,然后显式调用get_code时,最后的打印行将代码成功打印到屏幕上。
However, in my view, if I explicitly try to print that property, it's 'None' 但是,在我看来,如果我明确尝试打印该属性,则该属性为“无”
Here's what my view code looks like: 这是我的视图代码:
otc = OneTimeCode(
otc_usr_user_id = user.usr_user_id
)
otc.get_code()
pprint.pprint(vars(otc))
session.add(otc)
And the console output looks like this: 控制台输出如下所示:
0d097c
{'_sa_instance_state': <sqlalchemy.orm.state.InstanceState object at 0x50877d0>, 'otc_expire_time': '2015-02-13T10:56:14.244447', 'otc_usr_user_id': 1} 2014-08-14 22:56:14,245
INFO [sqlalchemy.engine.base.Engine][Dummy-2] INSERT INTO otc_one_time_codes (otc_one_time_code, otc_usr_user_id, otc_expire_time) VALUES (%(otc_one_time_code)s, %(otc_usr_user_id)s, %(otc_expire_time)s) RETURNING otc_one_time_codes.otc_one_time_code_id 2014-08-14 22:56:14,245
INFO [sqlalchemy.engine.base.Engine][Dummy-2] {'otc_one_time_code': None, 'otc_expire_time': '2015-02-13T10:56:14.244447', 'otc_usr_user_id': 1} 2014-08-14 22:56:14,247
INFO [sqlalchemy.engine.base.Engine][Dummy-2] COMMIT
You can see the value inside the model: 0d097c, and also the pprint object, where it doesn't look like the property exists. 您可以在模型内部看到值:0d097c,以及看起来不存在该属性的pprint对象。
Why can't I get access to this property? 为什么我无法访问此属性?
Looks like you should be using a @property
instead of a OTC
, however it also seems like this may be something you DON'T want to calculate each time! 看起来您应该使用
@property
而不是OTC
,但是似乎您不想每次都计算它!
# for all the docstrings, let multi = Multi(2)
class Multi(object):
def __init__(self, attribute):
"""When instantiated, set self.attribute to attribute"""
self.attribute = attribute
@property
def attribute_times_ten(self):
"""accessed via multi.attribute_times_ten
and will return 20. Use properties to signify
a variable that requires some work done to it
that needs to calculated each time it's called."""
return attribute_times_ten
@classmethod
def times_ten(cls, num):
"""Not the best example, but a @classmethod will
give the class as its first argument, NOT the
instance. This is useful in lots of constructor
settings, e.g. CreateClass.fromstring("attributes")"""
return num * 5
def generate_number(self, multiplier):
"""This is just a normal method. This is what I think
you want, tbh, and you should probably call it in your
__init__ method since you NEED this to run in your OTC
for it to work as intended. Methods (like properties)
are automagically passed the instance as the first
argument, so we can CHANGE self.attribute with that."""
self.attribute = self.attribute * multiplier
Docstrings should be self descriptive, but: 文档字符串应具有自我描述性,但:
multi = Multi(2)
multi.attribute_times_ten # returns 20
Multi.times_ten(8) # returns 80, note the capital M!
multi.generate_number(3) # self.attribute is now 6
multi.attribute_times_ten # returns 60
A real-world case where you might need all of the above: 在实际情况下,您可能需要以上所有条件:
class _Tile(object):
def __init__(self, x, y):
"""A naive implementation of Tile that doesn't care
what its side length is and doesn't have any properties
to hide its attributes"""
self.x = x
self.y = y
@classmethod
def tiles_to_pixels(cls, tile):
return cls(tile._x * tile.side_length, tile._y * tile.side_length)
@classmethod
def tiles_to_tiles(cls, tile):
return cls(tile._x, tile._y)
class Tile(object):
def __init__(self, x, y, side_length):
"""A tile object in a map"""
self._x = x # x-coord in tiles
self._y = y # y-coord in tiles
self.side_length = side_length # pixels per tile
@property
def in_pixels(self):
"""self.in_pixels returns an object whose .x and .y
correspond to the x and y position IN PIXELS of the
top-left corner of the tile."""
_tile = _Tile.tiles_to_pixels(self)
return _tile
@property
def in_tiles(self):
"""self.in_tiles returns an object whose .x and .y
correspond to the x and y position IN TILES of the
top-left corner of the tile."""
_tile = _Tile.tiles_to_tiles(self)
return _tile
def change_side_length(self, new_length):
"""Use to change the side length. This can break
your whole map since it's naive, so be careful."""
self.side_length = new_length
my_tile = Tile(0,0,32) # 32 pixel tile starting at (0,0)
my_tile.x # NameError, since it's called my_tile._x
my_tile.in_tiles.x # 0
my_tile.in_pixels.y # 0
other_tile = Tile(4,7,32) # 32 pixel tile starting at (4,7)
other_tile.y # NameError, see above
other_tile.in_tiles.y # 7
other_tile.in_pixels.x # 128
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