Unable to load pickle object from file

问题

I'm just trying out the pickle module and learning its functions and utilities. I've written this small piece of code, but it's giving me trouble.

import pickle
myfile = open("C:\\Users\\The Folder\\databin.txt", 'r+') #databin.txt is completely blank
class A:
    def __init__ (self):
        self.variable = 25
        self.random = 55
pickle.dump (A, myfile, -1) #HIGHEST_PROTOCOL 
pickle.load (myfile)

I then get the following error:

 Traceback (most recent call last):
File "<pyshell#9>", line 1, in <module>
pickle.load (myfile)
File "C:\Python27\lib\pickle.py", line 1378, in load
return Unpickler(file).load()
File "C:\Python27\lib\pickle.py", line 858, in load
dispatch[key](self)
KeyError: '\x00'

回答1:

You'd need to close the file first, then reopen it for that to work; and use binary mode to open your file.

Last but not least, pickle can store instances of classes only, not the classes themselves:

filename = "C:\\Users\\The Folder\\databin.txt"
with open(filename, 'wb') as myfile:
    pickle.dump(A(), myfile, -1) #HIGHEST_PROTOCOL 
with open(filename, 'rb') as myfile:
    pickle.load(myfile)

Here I've used the file as a context manager, it'll close automatically when the with suite is exited.

回答2:

Basically, what Martin says is correct. You need to close the file first, then reopen it. If you don't you get an error. I'm using dill, instead of pickle, so I can pickle the class.

Python 3.3.5 (default, Mar 10 2014, 21:37:38) 
[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.
>>> import dill
>>> myfile = open('pickle.pkl', 'rb+')
>>> 
>>> class A:
...   def __init__(self):
...     self.variable = 25
...     self.random = 55
... 
>>> dill.dump(A, myfile, 2)
>>> dill.load(myfile)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/mmckerns/lib/python3.3/site-packages/dill-0.2.2.dev-py3.3.egg/dill/dill.py", line 187, in load
    obj = pik.load()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/pickle.py", line 847, in load
    raise EOFError
EOFError

Now, close the file, and try again… remember to open it again first.

>>> myfile.close()
>>> dill.load(myfile)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/mmckerns/lib/python3.3/site-packages/dill-0.2.2.dev-py3.3.egg/dill/dill.py", line 187, in load
    obj = pik.load()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/pickle.py", line 845, in load
    key = read(1)
ValueError: read of closed file
>>> 
>>> myfile = open('pickle.pkl', 'rb+')
>>> dill.load(myfile)
<class '__main__.A'>

来源：https://stackoverflow.com/questions/11920792/unable-to-load-pickle-object-from-file

标签

python

pickle