Import a dictionary from a .dat file

Question

I have a .txt file with a list of countries and that countries information separated by commas. My problem is to use that file to create a dictionary, then save that dictionary to a pickled .dat file, and finally import that dictionary so the user can search a countries name and print the information.

I think I created the dictionary and saved it to the dat file correctly, I am having trouble importing the dictionary and searching through it. This is my code for creating and saving the dictionary:

    natDict = {}
with open("UN.txt","r") as filestream:
    for line in filestream:
        currentLine = line.split(",")
        newC = Nation(currentLine[0],currentLine[1],float(currentLine[2]),float(currentLine[3])) #creats new Nation object
        natDict[currentLine[0]] = newC

with open('nationsDict.dat', 'wb') as handle:
    pickle.dump(natDict, handle, protocol=pickle.HIGHEST_PROTOCOL)

Now I have to create a new program that uses the nationsDict.dat file so the user can search for countries. I don't have any experience with pickled dat files and my teacher's lecture slides don't say anything about them. I am guessing I have to import the dat file and then make it a dictionary again so that the user can search it, I just don't know how I am supposed to do it.

//Edit Sorry that the question is a bit unclear, I'll try and give more info. I created an object for each Nation so that the dictionary is like {CountryName: CountryObject}.

class Nation:
def __init__(self, name, cont, pop, area):
    self.name = name
    self.cont = cont
    self.pop = pop
    self.area = area
    self.popDens = self.calcPopDensity(pop,area)

def calcPopDensity(self,pop,area):
    return((pop * 1000000) / area)

def __str__(self):
    return (self.name + ":\ncontinent: " + self.cont + "\npopulation: " + str(self.pop) +
            " million \narea: " + str(self.area) + "\nPopulation Density : " + str(self.popDens))

The UN.txt file is setup like:
Afghanistan,Asia,31.8,251772
Albania,Europe,3.0,11100
Algeria,Africa,38.3,919595
Andorra,Europe,.085,181
Angola,Africa,19.1,481354

With all nations in the UN in the file.

All I really need to know is how I can use the nationsDict.dat file to search items. I put a dictionary in it, so could I just import it and use it like it is still a dictionary? Or do I have to create a dictionary again with the information in the .data file. Hope this helps.

Please provide a minimal, complete, and verifiable example. https://stackoverflow.com/help/mcve — Claus Wilke, Nov 26 '17 at 17:56
This problem could be solved with Python dicts, but since SQLite is built in, you might find it easier to use that. There's a fairly simple example in https://stackoverflow.com/questions/2887878/importing-a-csv-file-into-a-sqlite3-database-table-using-python — msw, Nov 26 '17 at 19:14

progmatico · Accepted Answer · 2017-11-26T19:08:14.333

Yes you open your .dat file, import your data (with pickle.load method) into your variables. You will also want to import (with import) your Nation class into the new program or you will get errors.

Edit: You can just save your objects, calling pickle.dump method with each one of the objects at a time, and then load them also one at a time. pickle will handle the types for you. But if you are loading a type of your own (defined with class) the source code for the class has to be available, thus the errors if it's not, and the need to import those classes into the loading script.

See a simple example and explanation here: https://wiki.python.org/moin/UsingPickle

You are welcome. I am sure I am not, that is why someone downvoted your question :) — progmatico, Nov 26 '17 at 19:09

Import a dictionary from a .dat file

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