What built in Python module can be used to convert an object to a stream of bytes that can be saved in a file?
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I´m trying to save and load objects using pickle module. Show After that I open a file called 'Fruits.obj'(previously I created a new .txt file and I renamed 'Fruits.obj'): >>> import pickle >>> filehandler = open(b"Fruits.obj","wb") >>> pickle.dump(banana,filehandler)After do this I close my session and I began a new one and I put the next (trying to access to the object that it supposed to be saved): file = open("Fruits.obj",'r') object_file = pickle.load(file)But I have this message: Traceback (most recent call last): File "I don´t know what to do because I don´t understand this message. Does anyone know How I can load my object 'banana'? Thank you! EDIT: As some of you have sugested I put: >>> import pickle >>> file = open("Fruits.obj",'rb')There were no problem, but the next I put was: >>> object_file = pickle.load(file)And I have error: Traceback (most recent call last): File "
martineau 115k25 gold badges160 silver badges282 bronze badges asked Dec 25, 2010 at 15:17
PeterstonePeterstone 6,63714 gold badges40 silver badges49 bronze badges 2 As for your second problem: Traceback (most recent call last): File "After you have read the contents of the file, the file pointer will be at the end of the file - there will be no further data to read. You have to rewind the file so that it will be read from the beginning again: file.seek(0)What you usually want to do though, is to use a context manager to open the file and read data from it. This way, the file will be automatically closed after the block finishes executing, which will also help you organize your file operations into meaningful chunks. Finally, cPickle is a faster implementation of the pickle module in C. So: In [1]: import _pickle as cPickle In [2]: d = {"a": 1, "b": 2} In [4]: with open(r"someobject.pickle", "wb") as output_file: ...: cPickle.dump(d, output_file) ...: # pickle_file will be closed at this point, preventing your from accessing it any further In [5]: with open(r"someobject.pickle", "rb") as input_file: ...: e = cPickle.load(input_file) ...: In [7]: print e ------> print(e) {'a': 1, 'b': 2}
alper 2,4555 gold badges42 silver badges75 bronze badges answered Dec 25, 2010 at 15:50
Jim BrissomJim Brissom 30.5k3 gold badges37 silver badges33 bronze badges 4 The following works for me: class Fruits: pass banana = Fruits() banana.color = 'yellow' banana.value = 30 import pickle filehandler = open("Fruits.obj","wb") pickle.dump(banana,filehandler) filehandler.close() file = open("Fruits.obj",'rb') object_file = pickle.load(file) file.close() print(object_file.color, object_file.value, sep=', ') # yellow, 30answered Dec 25, 2010 at 22:05
martineaumartineau 115k25 gold badges160 silver badges282 bronze badges 7 You're forgetting to read it as binary too. In your write part you have: open(b"Fruits.obj","wb") # Note the wb part (Write Binary)In the read part you have: file = open("Fruits.obj",'r') # Note the r part, there should be a b tooSo replace it with: file = open("Fruits.obj",'rb')And it will work :) As for your second error, it is most likely cause by not closing/syncing the file properly. Try this bit of code to write: >>> import pickle >>> filehandler = open(b"Fruits.obj","wb") >>> pickle.dump(banana,filehandler) >>> filehandler.close()And this (unchanged) to read: >>> import pickle >>> file = open("Fruits.obj",'rb') >>> object_file = pickle.load(file)A neater version would be using the with statement. For writing: >>> import pickle >>> with open('Fruits.obj', 'wb') as fp: >>> pickle.dump(banana, fp)For reading: >>> import pickle >>> with open('Fruits.obj', 'rb') as fp: >>> banana = pickle.load(fp)answered Dec 25, 2010 at 15:21
1 Always open in binary mode, in this case file = open("Fruits.obj",'rb')answered Dec 25, 2010 at 15:20
ismailismail 44.2k8 gold badges84 silver badges95 bronze badges You can use anycache to do the job for you. Assuming you have a function myfunc which creates the instance: from anycache import anycache class Fruits:pass @anycache(cachedir='/path/to/your/cache') def myfunc() banana = Fruits() banana.color = 'yellow' banana.value = 30 return bananaAnycache calls myfunc at the first time and pickles the result to a file in cachedir using an unique identifier (depending on the the function name and the arguments) as filename. On any consecutive run, the pickled object is loaded. If the cachedir is preserved between python runs, the pickled object is taken from the previous python run. The function arguments are also taken into account. A refactored implementation works likewise: from anycache import anycache class Fruits:pass @anycache(cachedir='/path/to/your/cache') def myfunc(color, value) fruit = Fruits() fruit.color = color fruit.value = value return fruitanswered Nov 19, 2017 at 19:50
c0fec0dec0fec0de 6218 silver badges4 bronze badges You didn't open the file in binary mode. open("Fruits.obj",'rb')Should work. For your second error, the file is most likely empty, which mean you inadvertently emptied it or used the wrong filename or something. (This is assuming you really did close your session. If not, then it's because you didn't close the file between the write and the read). I tested your code, and it works. answered Dec 25, 2010 at 15:21
Lennart RegebroLennart Regebro 161k41 gold badges219 silver badges250 bronze badges It seems you want to save your class instances across sessions, and using pickle is a decent way to do this. However, there's a package called klepto that abstracts the saving of objects to a dictionary interface, so you can choose to pickle objects and save them to a file (as shown below), or pickle the objects and save them to a database, or instead of use pickle use json, or many other options. The nice thing about klepto is that by abstracting to a common interface, it makes it easy so you don't have to remember the low-level details of how to save via pickling to a file, or otherwise. Note that It works for dynamically added class attributes, which pickle cannot do... dude@hilbert>$ python Python 2.7.6 (default, Nov 12 2013, 13:26:39) [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. >>> from klepto.archives import file_archive >>> db = file_archive('fruits.txt') >>> class Fruits: pass ... >>> banana = Fruits() >>> banana.color = 'yellow' >>> banana.value = 30 >>> >>> db['banana'] = banana >>> db.dump() >>>Then we restart… dude@hilbert>$ python Python 2.7.6 (default, Nov 12 2013, 13:26:39) [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. >>> from klepto.archives import file_archive >>> db = file_archive('fruits.txt') >>> db.load() >>> >>> db['banana'].color 'yellow' >>>Klepto works on python2 and python3. Get the code here: https://github.com/uqfoundation answered May 21, 2014 at 13:55
Mike McKernsMike McKerns 31.5k8 gold badges111 silver badges137 bronze badges Not the answer you're looking for? Browse other questions tagged python object pickle or ask your own question.What is pickle in Python used for?Pickle in Python is primarily used in serializing and deserializing a Python object structure. In other words, it's the process of converting a Python object into a byte stream to store it in a file/database, maintain program state across sessions, or transport data over the network.
What is .pickle file?Pickle can be used to serialize Python object structures, which refers to the process of converting an object in the memory to a byte stream that can be stored as a binary file on disk. When we load it back to a Python program, this binary file can be de-serialized back to a Python object.
What is pickle dump in Python?Python Pickle dump
dump() function to store the object data to the file. pickle. dump() function takes 3 arguments. The first argument is the object that you want to store. The second argument is the file object you get by opening the desired file in write-binary (wb) mode.
What is pickle module?The Python pickle module is another way to serialize and deserialize objects in Python. It differs from the json module in that it serializes objects in a binary format, which means the result is not human readable.
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