如何保存对象(数据持久性)?

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我创建了这样一个对象:

company1.name = 'banana' 
company1.value = 40

我想保存这个对象。我该怎么做?

提问于
用户回答回答于

可以pickle在标准库中使用该模块。以下是你的示例的基本应用:

import pickle

class Company(object):
    def __init__(self, name, value):
        self.name = name
        self.value = value

with open('company_data.pkl', 'wb') as output:
    company1 = Company('banana', 40)
    pickle.dump(company1, output, pickle.HIGHEST_PROTOCOL)

    company2 = Company('spam', 42)
    pickle.dump(company2, output, pickle.HIGHEST_PROTOCOL)

del company1
del company2

with open('company_data.pkl', 'rb') as input:
    company1 = pickle.load(input)
    print(company1.name)  # -> banana
    print(company1.value)  # -> 40

    company2 = pickle.load(input)
    print(company2.name) # -> spam
    print(company2.value)  # -> 42

也可以使用一个简单的实用程序,如下所示打开一个文件并向其中写入一个对象:

def save_object(obj, filename):
    with open(filename, 'wb') as output:
        pickle.dump(obj, output, pickle.HIGHEST_PROTOCOL)

# sample usage
save_object(company1, 'company1.pkl')

用户回答回答于

我认为假定对象是a是一个非常强烈的假设class。如果它不是class?还有一个假设,即对象在解释器中没有定义。如果在解释器中定义它会怎么样?另外,如果属性是动态添加的呢?当一些python对象的属性添加到它们的__dict__创建后,pickle并不考虑添加这些属性(即它'忘记'它们被添加 - 因为pickle通过引用对象定义进行序列化)。

在所有这些情况,pickle并且cPickle可以可怕的失败你。

如果你想保存一个object(任意创建的),你有属性(或者添加到对象定义中,或者之后)......你最好的选择就是使用dill,它可以在python中序列化几乎任何东西。

开始......

Python 2.7.8 (default, Jul 13 2014, 02:29:54) 
[GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import pickle
>>> class Company:
...     pass
... 
>>> company1 = Company()
>>> company1.name = 'banana'
>>> company1.value = 40
>>> with open('company.pkl', 'wb') as f:
...     pickle.dump(company1, f, pickle.HIGHEST_PROTOCOL)
... 
>>> 

现在关闭,然后重新启动...

Python 2.7.8 (default, Jul 13 2014, 02:29:54) 
[GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import pickle
>>> with open('company.pkl', 'rb') as f:
...     company1 = pickle.load(f)
... 
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 1378, in load
    return Unpickler(file).load()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 858, in load
dispatch[key](self)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 1090, in load_global
    klass = self.find_class(module, name)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 1126, in find_class
    klass = getattr(mod, name)
AttributeError: 'module' object has no attribute 'Company'
>>> 

糟糕...... pickle无法处理它。我们试试吧dill。我们会抛出另一个对象类型(a lambda)以获得更好的效果。

Python 2.7.8 (default, Jul 13 2014, 02:29:54) 
[GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import dill       
>>> class Company:
...     pass
... 
>>> company1 = Company()
>>> company1.name = 'banana'
>>> company1.value = 40
>>> 
>>> company2 = lambda x:x
>>> company2.name = 'rhubarb'
>>> company2.value = 42
>>> 
>>> with open('company_dill.pkl', 'wb') as f:
...     dill.dump(company1, f)
...     dill.dump(company2, f)
... 
>>> 

现在阅读文件。

Python 2.7.8 (default, Jul 13 2014, 02:29:54) 
[GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import dill
>>> with open('company_dill.pkl', 'rb') as f:
...     company1 = dill.load(f)
...     company2 = dill.load(f)
... 
>>> company1 
<__main__.Company instance at 0x107909128>
>>> company1.name
'banana'
>>> company1.value
40
>>> company2.name
'rhubarb'
>>> company2.value
42
>>>    

有用。原因pickle失败了,dill不是,就像dill对待__main__模块(大部分),也可以腌制类定义,而不是通过引用酸洗(如pickle同样)。原因dill可以腌制的lambda是,它给它一个名字...然后酸洗魔术可能会发生。

实际上,有一种更简单的方法来保存所有这些对象,尤其是在您创建了很多对象的情况下。只需转储整个python会话,稍后再回来。

Python 2.7.8 (default, Jul 13 2014, 02:29:54) 
[GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import dill
>>> class Company:
...     pass
... 
>>> company1 = Company()
>>> company1.name = 'banana'
>>> company1.value = 40
>>> 
>>> company2 = lambda x:x
>>> company2.name = 'rhubarb'
>>> company2.value = 42
>>> 
>>> dill.dump_session('dill.pkl')
>>> 

然后再回来......

Python 2.7.8 (default, Jul 13 2014, 02:29:54) 
[GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import dill
>>> dill.load_session('dill.pkl')
>>> company1.name
'banana'
>>> company1.value
40
>>> company2.name
'rhubarb'
>>> company2.value
42
>>> company2
<function <lambda> at 0x1065f2938>

唯一的主要缺点是dill不是Python标准库的一部分。所以如果你不能在你的服务器上安装python包,那么你不能使用它。

但是,如果你能够在系统上安装Python包,你可以得到最新的dillgit+https://github.com/uqfoundation/dill.git@master#egg=dill。你可以用最新版本发布pip install dill

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