Python: Read only dictionary

read-only-dict-1.py

class ReadOnlyDict(dict):
    def __setitem__(self, key, value):
        raise RuntimeError("Modification not supported")


rw_dict = {'key': 'original'}
print('Dict: ' + str(rw_dict))
ro_dict = ReadOnlyDict(rw_dict)
print('ReadOnlyDict: ' + str(ro_dict))

rw_dict['key'] = 'modified'
print('Dict: ' + str(rw_dict))
ro_dict['key'] = 'modified' # RuntimeError: Modification not supported
print('ReadOnlyDict: ' + str(ro_dict))

read-only-dict-2.py

import copy

def method(in_dict):
    print('Method: ' + str(in_dict))
    in_dict['key'] = 'modified'
    print('Method: ' + str(in_dict))


rw_dict = {'key': 'original'}
print('Original: ' + str(rw_dict))
method(copy.deepcopy(rw_dict))
print('Original: ' + str(rw_dict))

read-only-dict-3.py

from types import MappingProxyType

rw_dict = {'key': 'original'}
ro_dict = MappingProxyType(rw_dict)
# ro_dict['key'] = 'modified' # TypeError: 'mappingproxy' object does not support item assignment

rw_dict['key'] = 'modified'
print(ro_dict) # Output: {'key': 'modified'}

read-only-dict-4.py

import threading
import time
from types import MappingProxyType


def thread_function(name, in_dict):
    print("Thread %s: starting" % name)
    print("Thread %s: %s" % (name, str(in_dict)))
    print("Thread %s: wait for 5 seconds" % name)
    time.sleep(5)
    print("Thread %s: %s" % (name, str(in_dict)))
    print("Thread %s: finishing" % name)
    # in_dict['key'] = 'modified'  # TypeError: 'mappingproxy' object does not support item assignment


if __name__ == "__main__":
    rw_dict = {'key': 'original'}
    ro_dict = MappingProxyType(rw_dict)

    print("Main    : " + str(ro_dict))
    print("Main    : before creating thread")
    x = threading.Thread(target=thread_function, args=(1, ro_dict,))
    print("Main    : before running thread")
    x.start()
    print("Main    : wait for 2 seconds")
    time.sleep(2)
    rw_dict['key'] = 'modified'  # Modify value
    print("Main    : " + str(ro_dict))
    print("Main    : wait for the thread to finish")
    # x.join()
    print("Main    : all done")