Styjun

I have a python dictionary that has the below format

data = 'key1': 'value1',
 'key2': 'value2',
 'key3': 'value3'

I want this key3 value to point to the value of key1.
what i tried so far is
'key3': key1['value1'] or 'key3': data['key1'] and both of them seem to be invalid syntaxes.

Python doesn't support pointers like C/C++ does, but you could use lists to serve as references. To access the value, you'd index into the first element of the list.

data = 
 'key1': ['value1']


data['key3'] = data['key1'] # copy the list by reference
print(f"Old: data['key3'][0], data['key3'][0] == data['key1'][0]")

data['key1'][0] = 'new-value' # this will modify the value from data['key3'] as well 
print(f"New: data['key3'][0], data['key3'][0] == data['key1'][0]")

Output:

Old: value1, True
New: new-value, True

Note that, this assumes that you're fully aware of which values act as "pointers" and which ones don't.

For example,

data = 
 'key1': ['pointer-list'], # should act as a "pointer"
 'key2': ['normal', 'list'] # should act as a normal list


data['key3'] = data['key1'] # copy list by reference
data['key1'][0] = 'new-value' # propogate new value to other references

data['key4'] = data['key2'] # oops – copy list by reference
data['key2'][0] = 'new-value' # oops – data['key2'] should act as a normal list but
 # the new value is propogated to data['key4'] as well

To deal with this issue, clone or copy the list instead.

import copy
data['key4'] = copy.copy(data['key2'])

# data['key4'] = copy.deepcopy(data['key2']) # if the value contains nested lists
# data['key4'] = data['key2'].copy() # another way

Try this

data = 'key1': 'value1', 'key2': 'value2', 'key3': 'value3' 

data['key3'] = data['key1']

print(data)

Prints out:

'key3': 'value1', 'key2': 'value2', 'key1': 'value1'