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

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

If you want a dictionary you can import from a file by name, and also that adds entries that are nicely sorted, and contains strings you want to preserve, you can try this:

data = {'A': 'a', 'B': 'b', }

with open('file.py','w') as file:
    file.write("dictionary_name = { \n")
    for k in sorted (data.keys()):
        file.write("'%s':'%s', \n" % (k, data[k]))
    file.write("}")

Then to import:

from file import dictionary_name

I know this is an old question but I also thought to share a solution that doesn't involve json. I don't personally quite like json because it doesn't allow to easily append data. If your starting point is a dictionary, you could first convert it to a dataframe and then append it to your txt file:

import pandas as pd
one_line_dict = exDict = {1:1, 2:2, 3:3}
df = pd.DataFrame.from_dict([one_line_dict])
df.to_csv('file.txt', header=False, index=True, mode='a')

I hope this could help.

fout = "/your/outfile/here.txt"
fo = open(fout, "w")

for k, v in yourDictionary.items():
    fo.write(str(k) + ' >>> '+ str(v) + '\n\n')

fo.close()

The probelm with your first code block was that you were opening the file as 'r' even though you wanted to write to it using 'w'

with open('/Users/your/path/foo','w') as data:
    data.write(str(dictionary))

You can do as follow :

import json
exDict = {1:1, 2:2, 3:3}
file.write(json.dumps(exDict))

https://developer.rhino3d.com/guides/rhinopython/python-xml-json/

import json

with open('tokenler.json', 'w') as file:
     file.write(json.dumps(mydict, ensure_ascii=False))

For list comprehension lovers, this will write all the key : value pairs in new lines in dog.txt

my_dict = {'foo': [1,2], 'bar':[3,4]}

# create list of strings
list_of_strings = [ f'{key} : {my_dict[key]}' for key in my_dict ]

# write string one by one adding newline
with open('dog.txt', 'w') as my_file:
    [ my_file.write(f'{st}\n') for st in list_of_strings ]

I do it like this in python 3:

with open('myfile.txt', 'w') as f:
    print(mydictionary, file=f)

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