New To Python (Programming) and Data Storage

I have a question about data storage. I开发者_运维知识库 have a program that is creating a list of objects. What is the best way to store these on file so that the program can reload them later? I've tried to use Pickle, but I think I might be heading down the wrong alley and I keep getting this error when I try to read back the data:

    Traceback (most recent call last):
     File "test.py", line 110, in <module>
knowledge = pickle.load(open("data.txt"))
    File "/sw/lib/python3.1/pickle.py", line 1356, in load
 encoding=encoding, errors=errors).load()
File "/sw/lib/python3.1/codecs.py", line 300, in decode
(result, consumed) = self._buffer_decode(data, self.errors, final)
  UnicodeDecodeError: 'utf8' codec can't decode byte 0x80 in position 0: invalid start byte

Edited to add: here's a bit of the code I'm trying:

FILE = open("data.txt", "rb")

knowledge = pickle.load(open("data.txt"))

FILE = open("data.txt", 'wb')

pickle.dump(knowledge, FILE)

---

I think the problem is that the line

knowledge = pickle.load(open("data.txt"))

doesn't open the file in binary mode. Python 3.2:

>>> import pickle
>>> 
>>> knowledge = {1:2, "fred": 19.3}
>>> 
>>> with open("data.txt", 'wb') as FILE:
...     pickle.dump(knowledge, FILE)
... 
>>> knowledge2 = pickle.load(open("data.txt"))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/codecs.py", line 300, in decode
    (result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf8' codec can't decode byte 0x80 in position 0: invalid start byte
>>> knowledge2 = pickle.load(open("data.txt","rb"))
>>> knowledge2
{1: 2, 'fred': 19.3}

---

No need to rewrite shelve, Python's object persistence library. Example:

import shelve

d = shelve.open(filename) # open -- file may get suffix added by low-level
                          # library

d[key] = data   # store data at key (overwrites old data if
                # using an existing key)
data = d[key]   # retrieve a COPY of data at key (raise KeyError if no
                # such key)
del d[key]      # delete data stored at key (raises KeyError
                # if no such key)
flag = d.has_key(key)   # true if the key exists
klist = d.keys() # a list of all existing keys (slow!)

# as d was opened WITHOUT writeback=True, beware:
d['xx'] = range(4)  # this works as expected, but...
d['xx'].append(5)   # *this doesn't!* -- d['xx'] is STILL range(4)!

# having opened d without writeback=True, you need to code carefully:
temp = d['xx']      # extracts the copy
temp.append(5)      # mutates the copy
d['xx'] = temp      # stores the copy right back, to persist it

# or, d=shelve.open(filename,writeback=True) would let you just code
# d['xx'].append(5) and have it work as expected, BUT it would also
# consume more memory and make the d.close() operation slower.

d.close()       # close it

---

If you're just want to recreate some class objects later, the easiest solution would be to dump their properties into a file and them read them back, creating the objects based on the contents.

See: http://docs.python.org/tutorial/inputoutput.html

---

You can use cPickle, or Picke it doesn't matter. Open in binary mode (rb) , and try setting the protocol to -1.

Try something like this:

import cPickle

my_file= open('wohoo.file', 'wb')

largeObject=  Magic() #insert your logic here
cPickle.dump(largeObject, my_file, -1)
my_file.close()

other_file = open('wohoo.file', 'rb')
welcomeBack - cPickle.load(other_file )
other_file.close()