How to pickle and unpickle

Question

import  pickle
variety = ["sweet", "box", "cat"]
shape = ["back","spear", "log"]
pickleFile = open("pickle.txt", 'w')
pickle.dump(variety, pickleFile)
pickle.dump(shape, pickleFile)
pickleFile.close()

pickleFile = open("pickle.txt", 'r')
test = pickle.load(pickleFile)
shape = pickle.load(pickleFile)

print ("variety : ", test, " shape : ", shape)
pickleFile.close()

when I run above code I get the following error

line 6, in <module>
pickle.dump(variety, pickleFile)
TypeError: must be str, not bytes

and i am not sure if unpickling in variable 'test' will be possible or not cause I had pickled in with variable 'variety'

Answer 1

According to help(pickle.dump),

The file argument must have a write() method that accepts a single bytes argument. It can thus be a file object opened for binary writing, a io.BytesIO instance, or any other custom object that meets this interface.

Looks like you have to open your file in binary mode. Don't forget to do the same for loading too.

import  pickle
variety = ["sweet", "box", "cat"]
shape = ["back","spear", "log"]
pickleFile = open("pickle.txt", 'wb')
pickle.dump(variety, pickleFile)
pickle.dump(shape, pickleFile)
pickleFile.close()

pickleFile = open("pickle.txt", 'rb')
test = pickle.load(pickleFile)
shape = pickle.load(pickleFile)

print ("variety : ", test, " shape : ", shape)
pickleFile.close()

Result:

variety :  ['sweet', 'box', 'cat']  shape :  ['back', 'spear', 'log']

Answer 2

Your problem is that you are trying to write a pickled object into a text file. That is like trying to write a database in MS word.

The correct file extension for a pickled file is '.pkl'. The file must also be written to and read from in binary mode.

My suggestion would be to change the file extensions to '.pkl' and then use two with loops to neaten up your code. The corrections to the loading and writing is as simple as changing 'w' to 'wb' The result looks like this:

import  pickle
variety = ["sweet", "box", "cat"]
shape = ["back","spear", "log"]
with open("pickle.pkl", 'wb') as pickleFile:
    pickle.dump(variety, pickleFile)
    pickle.dump(shape, pickleFile)
    pickleFile.close()

with open("pickle.pkl", 'rb') as pickleFile:
    test = pickle.load(pickleFile)
    shape = pickle.load(pickleFile)

print ("variety : ", test, " shape : ", shape)
pickleFile.close()