How to parse pickle dictionary in Python?

Question

I am working with a dictionary. From different resources, I understood that is comfortable to use pickle. I want to use pickle to save triples like: subject: predicate: object, but later I want to load them and fill an array Assuming, my code:

import pickle

file_name = 'fna.txt'

class DictClass:
    def __init__(self, subj, predicate, obj ):
        self.subj = subj
        self.predicate = predicate
        self.obj = obj
    def __repr__(self):
        return 'DictClass(%r, %r, %r)' % (self.subj, self.predicate, self.obj)
    def __eq__(self, other):
        return (self.subj == other.subj) and (self.predicate == other.predicate) and (self.obj == other.obj)

data = {'triple': DictClass(17,'subClassOf', 34), 'triple': DictClass(22,'subClassOf', 44)}

print('data:', data)
print('repr(data):', repr(data))
print("data == eval(repr(data), {'DictClass':DictClass})?:", data == eval(repr(data), {'DictClass':DictClass}))

# Load the dictionary back from the pickle file.  
def ld_dict(fname):
    reader = pickle.load(open(fname, 'rb'))
    print(reader)
    return True

# Save a dictionary into a pickle file.
def sv_dict(fname):
    pickle.dump( data, open( fname, "wb" ) )
    return True

if(sv_dict(file_name)):
    print('File saved!')

if(ld_dict(file_name)):
    print('File loaded!')

In generally, I want to save data in the dictionary and later load it and make some processing about it but I have a problem. I cannot access to the information into the loaded data. In function ld_dict I was trying to read information and have results:

data: {'triple': DictClass(22, 'subClassOf', 44)}
repr(data): {'triple': DictClass(22, 'subClassOf', 44)}
data == eval(repr(data), {'DictClass':DictClass})?: True
File saved!
triple
File loaded!

How I can get information in the way like, for example, JSON. How to parse JSON I found here(How to parse json data in Python?). Also, I have seen this resource: how to save a dictionary in pickle Thank you for help

Because you open your files inside the loops, they will only store the last entry in your data dict(). Open your file prior to entering your loops and close it after. — Alan Leuthard, May 23 '17 at 21:13
data is also overwriting the 'triple' key with it's second entry, so it only has 1 entry — Alan Leuthard, May 23 '17 at 21:54
Don't use a loop to save your dict. Just save it: pickle.dump(data, file_writemode), and open it: reader = pickle.load(file_readmode) — Alan Leuthard, May 23 '17 at 22:00

stovfl · Accepted Answer · 2017-05-24T18:52:51.447

Comment: ... but I cannot see : 'triple': DictClass(17, 'subClassOf', 34)

There is no 'triple': DictClass(17, 'subClassOf', 34) in your example data, because your example dict data is invalid!
Keys in a dict have to be unique, you overwrite the first 'triple' with the second 'triple'. Maybe you want a list instead of a dict.

Question: I cannot access to the information into the loaded data.

You get the same data object back, assing it to a variable to become a instance.

Note: I use in Memory dumps/loads, replace with dump/load to write/read to/from file.

This is working for me, for instance:

def print_data(d):
    print('data:', d)
    print('repr(data):', repr(d))
    print("data == eval(repr(data), {'DictClass':DictClass})?:", data == eval(repr(d), {'DictClass':DictClass}))
    print('\n')

data = {'triple': DictClass(17, 'subClassOf', 34), 'triple': DictClass(22, 'subClassOf', 44)}
print_data(data)

#pickle.dump( data, open( fname, "wb" ) )
data_pickeld = pickle.dumps( data )

#data_unpickeld = pickle.load(open(fname, 'rb'))
data_unpickeld = pickle.loads( data_pickeld)

print_data(data_unpickeld)

Output:
data: {'triple': DictClass(22, 'subClassOf', 44)}
repr(data): {'triple': DictClass(22, 'subClassOf', 44)}
data == eval(repr(data), {'DictClass':DictClass})?: True

data: {'triple': DictClass(22, 'subClassOf', 44)}
repr(data): {'triple': DictClass(22, 'subClassOf', 44)}
data == eval(repr(data), {'DictClass':DictClass})?: True

Tested with Python: 3.4.2

Yes, you're right here, but I cannot see : 'triple': DictClass(17, 'subClassOf', 34) — Vasyl Lyashkevych, May 24 '17 at 18:25

How to parse pickle dictionary in Python?

1 Answers1