change dictionary value python

my_dict  =  {
   'foo': 42,
   'bar': 12.5
}
my_dict['foo']  =  "Hello"
print(my_dict['foo'])
#This will give the output:

'Hello'

>>> dictionary = { 1: 'one', 2:'two', 3:'three' }
>>> dictionary['ONE'] = dictionary.pop(1)
>>> dictionary
{2: 'two', 3: 'three', 'ONE': 'one'}
>>> dictionary['ONE'] = dictionary.pop(1)
Traceback (most recent call last):
  File "<input>", line 1, in <module>
KeyError: 1

dict = {value:key for key, value in dict.items()}