how to save/read class wholly in Python

Question

som = SOM_CLASS() # includes many big difficult data structures
som.hard_work()
som.save_to_disk(filename)
#then later or another program
som = SOM_CLASS()
som.read_from_file(filename)
som.do_anythink_else()

or

som = SOM_CLASS()
save(som)
#...
load(som)
som.work()

what is easiest way to do this?

Any other requirement? Speed/size/security/portability? http://docs.python.org/library/json.html could be an option. — Esteban Küber, Feb 26 '10 at 22:07
You should change this to "how to save/read object wholly in Python" — Nicolas Shu, Mar 15 '21 at 19:11

score 31 · Accepted Answer · answered Feb 26 '10 at 22:12

You can (de)serialize with pickle. It is backward-compatible, i.e. it will support all old protocols in future versions.

import pickle

som = SOM_CLASS()
fileObject = <any file-like object>
pickle.dump(som, fileObject)
#...
som = pickle.load(fileObject)
som.work()

But mind that if you transfer pickled objects to another computer, make sure the connection cannot be tampered with as pickle might be unsecure (this is an article that every pickle user should know).

Another alternative is the older module marshal.

Nadia... Answering even when offline :) http://stackoverflow.com/users/97828/nadia-alramli — Esteban Küber, Feb 26 '10 at 22:16

score 14 · Answer 2 · answered Feb 08 '12 at 21:29

I use this code:

import cPickle
import traceback

class someClass():
    def __init__(self):
        #set name from variable name. http://stackoverflow.com/questions/1690400/getting-an-instance-name-inside-class-init
        (filename,line_number,function_name,text)=traceback.extract_stack()[-2]
        def_name = text[:text.find('=')].strip()
        self.name = def_name

        try:
            self.load()
        except:
            ##############
            #to demonstrate
            self.someAttribute = 'bla'
            self.someAttribute2 = ['more']
            ##############

            self.save()

    def save(self):
        """save class as self.name.txt"""
        file = open(self.name+'.txt','w')
        file.write(cPickle.dumps(self.__dict__))
        file.close()

    def load(self):
        """try load self.name.txt"""
        file = open(self.name+'.txt','r')
        dataPickle = file.read()
        file.close()

        self.__dict__ = cPickle.loads(dataPickle)

This code saves and loads the class from its actual class instance name. Code is from my blog http://www.schurpf.com/python-save-a-class/.

Excellent! Exactly what I wanted. – markroxor Mar 26 '18 at 06:44 — markroxor, Mar 26 '18 at 06:44
Brilliant, I wish I had thought of this myself! :) – Jim Jam Jan 09 '20 at 13:55 — Jim Jam, Jan 09 '20 at 13:55

score 2 · Answer 3 · answered Feb 26 '10 at 22:05

2

Take a look at Python's pickle library.

answered Feb 26 '10 at 22:05

Amber

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score 1 · Answer 4 · answered Feb 24 '21 at 17:41

Use pickle in this way:

import pickle
class Student:
    def __init__(self, name, age, grade):
        self.name = name
        self.age = age
        self.grade = grade # 0 - 100
    def get_grade(self):
        print (self.grade)
s1 = Student("Tim", 19, 95)

#save it
with open(f'test.pickle', 'wb') as file:
    pickle.dump(s1, file) 

#load it
with open(f'test.pickle', 'rb') as file2:
    s1_new = pickle.load(file2)

#check it
s1_new.get_grade()
# it prints 95

how to save/read class wholly in Python

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