Python pickle module usage Example Analysis

Python pickle module usage Example Analysis

This example describes how to use the Python pickle module. Share it with you for your reference. The specific analysis is as follows:

Pickle provides a simple persistence function. Objects can be stored on disks as files.

Pickle. dump (obj, file [, protocol])

Serialize the object and write the result data stream to the file object. The protocol parameter is a serialization mode. The default value is 0, indicating serialization in text format. The value of protocol can also be 1 or 2, indicating that the protocol is serialized in binary format.

Pickle. load (file)

Deserialization object. Parses the data in the file into a Python object.

Note that when loading (file), python should be able to find the class definition; otherwise, an error will be reported:

For example

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Import pickle Class Person: Def _ init _ (self, n, ): Self. name = n Self. age = Def show (self ): Print self. name + "_" + str (self. age) Aa = Person ("JGood", 2) Aa. show () F = open ('d: p.txt ', 'w ') Pickle. dump (aa, f, 0) F. close () # Del Person F = open ('d: p.txt ', 'R ') Bb = pickle. load (f) F. close () Bb. show ()

If del Person is not commented out, the following error is returned:

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>>> JGood_2   Traceback (most recent call last ): File "C:/py/test. py", line 15, in <module> Bb = pickle. load (f) File "C: Python27libpickle. py", line 1378, in load Return Unpickler (file). load () File "C: Python27libpickle. py", line 858, in load Dispatch [key] (self) File "C: Python27libpickle. py", line 1069, in load_inst Klass = self. find_class (module, name) File "C: Python27libpickle. py", line 1126, in find_class Klass = getattr (mod, name) AttributeError: 'module' object has no attribute 'person'

This means that the class definition cannot be found in the current module.

Clear_memo ()

Empty pickler's "Memo ". When using the Pickler instance to serialize an object, it will "remember" The object that has been serialized is referenced, so the same object is called multiple times dump (obj ), pickler won't perform multiple serialization as silly.

See the following example:

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Import StringIO Import pickle Class Person: Def _ init _ (self, n, ): Self. name = n Self. age = Def show (self ): Print self. name + "_" + str (self. age) Aa = Person ("JGood", 2) Aa. show () Fle = StringIO. StringIO () Pick = pickle. Pickler (fle) Pick. dump (aa) Val1 = fle. getvalue () Print len (val1) Pick. clear_memo () Pick. dump (aa) Val2 = fle. getvalue () Print len (val2) Fle. close ()

The above code runs as follows:

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>>> JGood_2 66 132 >>>

After pick. clear_memo () is commented out, the running result is as follows:

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>>> JGood_2 66 70 >>>

The main reason is that python pickle does not serialize objects multiple times without clear_memo.

I hope this article will help you with Python programming.