Can I pickle Python objects in memory instead of a physical file? [duplicate]

Question

I have seen and written code to pickle objects in Python. But they all create physical file to contain data. I want that I write the data in memory and read it and pickle it and transfer it.

Is it even possible ?

from PIL import ImageGrab
import io
import codecs
import pickle


# Model class to send Process Data to the server
class ProcessData:
 process_id = 0
 project_id = 0
 task_id = 0
 start_time = 0
 end_time = 0
 user_id = 0
 weekend_id = 0

# Model class to send image data to the server
class ProcessScreen:
 process_id = 0
 image_data = bytearray()


image_name = "Dharmindar_screen.jpg"
ImageGrab.grab().save(image_name,"JPEG")

image_data = None
with codecs.open(image_name,'rb') as image_file:
 image_data = image_file.read()



serialized_process_data = io.BytesIO()

process_data = ProcessData()
process_data.process_id = 1
process_data.project_id = 2
process_data.task_id = 3
process_data.user_id = 4
process_data.weekend_id = 5
process_data.start_time = 676876
process_data.end_time = 787987

process_screen = ProcessScreen()
process_screen.process_id = process_data.process_id
process_screen.image_data = image_data


prepared_process_data = (process_data, process_screen)

process_data_serializer = pickle.Pickler()
process_data_serializer(serialized_process_data).dump(prepared_process_data)

print('Data serialized.')


if process_data_serializer is not None:
    d = process_data_serializer.getvalue()
    deserialized_data = None
    with open(d, 'rb') as serialized_data_file:
        process_deserializer = pickle.Unpickler(serialized_data_file)
        deserialized_data = process_deserializer.load()
else:
    print('Empty')

The above code throws the TypeError: Required argument 'file' (pos 1) not found

Answer 1

The File object you pass to pickle.dump just needs a write method, see https://docs.python.org/2/library/pickle.html#pickle.dump

file must have a write() method that accepts a single string argument. It can thus be a file object opened for writing, a StringIO object, or any other custom object that meets this interface.

Instead of using a StringIO object, you could even create your own class to store the pickled data, for example

class MyFile(object):
    def __init__(self):
        self.data = []
    def write(self, stuff):
        self.data.append(stuff)

and then just pickle to an instance of this class:

class ExampleClass(object):
    def __init__(self, x):
        self.data = x  
a = ExampleClass(123)
f = MyFile()
pickle.dump(a, f)

Another option is, as proposed by @rawing, is to use pickle.dumps which will directly return a string that you can use, compare here.