Save a dictionary to a file (alternative to pickle) in Python?

Question

Answered I ended up going with pickle at the end anyway

Ok so with some advice on another question I asked I was told to use pickle to save a dictionary to a file.

The dictionary that I was trying to save to the file was

members = {'Starspy' : 'SHSN4N', 'Test' : 'Test1'}

When pickle saved it to the file... this was the format

(dp0
S'Test'
p1
S'Test1'
p2
sS'Test2'
p3
S'Test2'
p4
sS'Starspy'
p5
S'SHSN4N'
p6
s.

Can you please give me an alternative way to save the string to the file?

This is the format that I would like it to save in

members = {'Starspy' : 'SHSN4N', 'Test' : 'Test1'}

Complete Code:

import sys
import shutil
import os
import pickle

tmp = os.path.isfile("members-tmp.pkl")
if tmp == True:
    os.remove("members-tmp.pkl")
shutil.copyfile("members.pkl", "members-tmp.pkl")

pkl_file = open('members-tmp.pkl', 'rb')
members = pickle.load(pkl_file)
pkl_file.close()

def show_menu():
    os.system("clear")
    print "\n","*" * 12, "MENU", "*" * 12
    print "1. List members"
    print "2. Add member"
    print "3. Delete member"
    print "99. Save"
    print "0. Abort"
    print "*" * 28, "\n"
    return input("Please make a selection: ")

def show_members(members):
    os.system("clear")
    print "\nNames", "     ", "Code"
    for keys in members.keys():
        print keys, " - ", members[keys]

def add_member(members):
    os.system("clear")
    name = raw_input("Please enter name: ")
    code = raw_input("Please enter code: ")
    members[name] = code
    output = open('members-tmp.pkl', 'wb')
    pickle.dump(members, output)
    output.close()
    return members


#with open("foo.txt", "a") as f:
#     f.write("new line\n")

running = 1

while running:
    selection = show_menu()
    if selection == 1:
        show_members(members)
        print "\n> " ,raw_input("Press enter to continue")
    elif selection == 2:
        members == add_member(members)
        print members
        print "\n> " ,raw_input("Press enter to continue")
    elif selection == 99:
        os.system("clear")
        shutil.copyfile("members-tmp.pkl", "members.pkl")
        print "Save Completed"
        print "\n> " ,raw_input("Press enter to continue")

    elif selection == 0:
        os.remove("members-tmp.pkl")
        sys.exit("Program Aborted")
    else:
        os.system("clear")
        print "That is not a valid option!"
        print "\n> " ,raw_input("Press enter to continue")

Solution 1

The most common serialization format for this nowadays is JSON, which is universally supported and represents simple data structures like dictionaries very clearly.

>>> members = {'Starspy' : 'SHSN4N', 'Test' : 'Test1'}
>>> json.dumps(members)
'{"Test": "Test1", "Starspy": "SHSN4N"}'
>>> json.loads(json.dumps(members))
{u'Test': u'Test1', u'Starspy': u'SHSN4N'}

Solution 2

Sure, save it as CSV:

import csv
w = csv.writer(open("output.csv", "w"))
for key, val in dict.items():
    w.writerow([key, val])

Then reading it would be:

import csv
dict = {}
for key, val in csv.reader(open("input.csv")):
    dict[key] = val

Another alternative would be json (json for version 2.6+, or install simplejson for 2.5 and below):

>>> import json
>>> dict = {"hello": "world"}
>>> json.dumps(dict)
'{"hello": "world"}'

Solution 3

The YAML format (via pyyaml) might be a good option for you:

http://en.wikipedia.org/wiki/Yaml

http://pypi.python.org/pypi/PyYAML

Solution 4

Although, unlike pp.pprint(the_dict), this won't be as pretty, will be run together, str() at least makes a dictionary savable in a simple way for quick tasks:

f.write( str( the_dict ) )

Solution 5

You asked

Ill give it a shot. How do I specify what file to dump it to/load it from?

Apart from writing to a string, the json module provides a dump()-method, which writes to a file:

>>> a = {'hello': 'world'}
>>> import json
>>> json.dump(a, file('filename.txt', 'w'))
>>> b = json.load(file('filename.txt'))
>>> b
{u'hello': u'world'}

There is a load() method for reading, too.

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