python 3.x - Writing a dictionary to a text file?

Question

I have a dictionary and am trying to write it to a file.

exDict = {1:1, 2:2, 3:3}
with open('file.txt', 'r') as file:
    file.write(exDict)

I then have the error

file.write(exDict)
TypeError: must be str, not dict

So I fixed that error but another error came

exDict = {111:111, 222:222}
with open('file.txt', 'r') as file:
    file.write(str(exDict))

The error:

file.write(str(exDict))
io.UnsupportedOperation: not writable

I have no idea what to do as I am still a beginner at python. If anyone knows how to resolve the issue, please provide an answer.

NOTE: I am using python 3, not python 2

Answer 1

First of all you are opening file in read mode and trying to write into it. Consult - IO modes python

Secondly, you can only write a string to a file. If you want to write a dictionary object, you either need to convert it into string or serialize it.

import json

# as requested in comment
exDict = {'exDict': exDict}

with open('file.txt', 'w') as file:
     file.write(json.dumps(exDict)) # use `json.loads` to do the reverse

In case of serialization

import cPickle as pickle

with open('file.txt', 'w') as file:
     file.write(pickle.dumps(exDict)) # use `pickle.loads` to do the reverse

For python 3.x pickle package import would be different

import _pickle as pickle