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 or bytes 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