How to replace nested python dictionary value from a key as a string format with separated by dots?

Question

a = {
    'user': {
        'username': 'mic_jack',    
        'name': {
            'first': 'Micheal',
            'last': 'Jackson'
        },
        'email': '[email protected]',

        #...
        #... Infinite level of another nested dict
    }     
}

str_key_1 = 'user.username=john'
str_key_2 = 'user.name.last=henry'
#...
#str_key_n = 'user.level2.level3...leveln=XXX'

Let's consider this 'str_key' string, goes with infinite number of dots/levels.

Expected Output:

a = {
    'user': {
        'username': 'john',     # username, should be replace    
        'name': {
            'first': 'Micheal',
            'last': 'henry'     # lastname, should be replace 
        },
        'email': '[email protected]',

        ...
        ... # Infinite level of another nested dict
    }     
}

I'm expecting the answers for applying 'n' Level of nested key string, rather than simply replacing by a['user']['username'] = 'John' statically. Answers must be work for any number of 'dotted' string values.

Thanks in advance!

Really feels like an XY problem, what are you trying to accomplish? — ruohola
– ruohola, Commented Jan 18, 2019 at 13:15
Are you saying you want a string for every possible combination of depth through n nested dicts? — KuboMD
– KuboMD, Commented Jan 18, 2019 at 13:15
@ruohola I have a 'config' dictionary object in 'config.py'. The user have the option to override this value from 'command line' like (e.g python run.py env=dev user.name.last=John) — Jeyakumar Kasi
– Jeyakumar Kasi, Commented Jan 18, 2019 at 13:18
@JaiK have you considered that your config dictionary could be in a simpler format? — ruohola
– ruohola, Commented Jan 18, 2019 at 13:20
@ruohola Some time, I want to group them as a single unit, For example, the config for 'Database' are grouped into db: {'HOST'='X', 'PORT': 8080, 'USERNAME': 'XXX', 'PASSWORD': 'YYY'}, destination output is grouped into dest: {'DIR_PATH': '/output', 'FILE_EXT': 'csv'} etc — Jeyakumar Kasi
– Jeyakumar Kasi, Commented Jan 18, 2019 at 13:23

wilsonzlin · Accepted Answer · 2019-01-18 13:41:44Z

2

There are three steps:

Separate the key-value pair string into a fully-qualified key and value.
Split the key into path components.
Traverse the dictionary to find the relevant value to update.

Here's an example of what the code might look like:

# Split by the delimiter, making sure to split once only
# to prevent splitting when the delimiter appears in the value
key, value = str_key_n.split("=", 1)

# Break the dot-joined key into parts that form a path
key_parts = key.split(".")

# The last part is required to update the dictionary
last_part = key_parts.pop()

# Traverse the dictionary using the parts
current = a
while key_parts:
  current = current[key_parts.pop(0)]

# Update the value
current[last_part] = value

answered Jan 18, 2019 at 13:41

wilsonzlin

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2 Comments

Jeyakumar Kasi Over a year ago

Is there any particular reason for using this temp. var current = a, because of without this assignment also the above code is working. I meant, directly using 'a' instead of 'current'.

Abdul Majeed Over a year ago

@jai without assignment a will become "{'first': 'Micheal', 'last': 'henry'}"

fixatd · Accepted Answer · 2019-01-18 14:03:35Z

I'd go with a recursive function to accomplish this, assuming your key value strings are all valid:

def assign_value(sample_dict, str_keys, value):
  access_key = str_keys[0]

  if len(str_keys) == 1:
    sample_dict[access_key] = value
  else:
    sample_dict[access_key] = assign_value(sample_dict[access_key], str_keys[1:], value)

  return sample_dict

The idea is to traverse your dict until you hit the lowest key and then we assign our new value to that last key;

if __name__ == "__main__":
  sample_dict = {
      'user': {
          'username': 'mic_jack',    
          'name': {
              'first': 'Micheal',
              'last': 'Jackson'
          },
          'email': '[email protected]'
      }     
  }

  str_key_1 = 'user.username=john'
  str_keys_1, value_1 = str_key_1.split('=')
  sample_dict = assign_value(sample_dict, str_keys_1.split('.'), value_1)

  print("result: {} ".format(sample_dict))


  str_key_2 = 'user.name.last=henry'
  str_keys_2, value_2 = str_key_2.split('=')
  sample_dict = assign_value(sample_dict, str_keys_2.split('.'), value_2)

  print("result: {}".format(sample_dict))

To use the assign_value you would need to split your original key to the keys and value as seen above;

Sanchit Mathew · Accepted Answer · 2019-01-18 14:55:59Z

If you're okay with using exec() and modify your str_key(s), you could do something like:

def get_keys_value(string):
    keys, value = string.split("=")
    return keys, value

def get_exec_string(dict_name, keys):
    exec_string = dict_name
    for key in keys.split("."):
        exec_string = exec_string + "[" + key + "]"
    exec_string = exec_string + "=" + "value"
    return exec_string

str_key_1 = "'user'.'username'=john"
str_key_2 = "'user'.'name'.'last'=henry"
str_key_list = [str_key_1, str_key_2]

for str_key in str_key_list:
    keys, value = get_keys_value(str_key) # split into key-string and value
    exec_string = get_exec_string("a", keys) # extract keys from key-string 
    exec(exec_string)

print(a)
# prints {'user': {'email': '[email protected]', 'name': {'last': 'henry', 'first': 'Micheal'}, 'username': 'john'}}

Faisal · Accepted Answer · 2019-01-21 09:25:16Z

str_key_1 = 'user.username=john'
str_key_2 = 'user.name.last=henry'

a = {
    'user': {
        'username': 'mic_jack',    
        'name': {
            'first': 'Micheal',
            'last': 'Jackson'
        },
        'email': '[email protected]',

        #...
        #... Infinite level of another nested dict
    }     
}

def MutateDict(key):
    strkey, strval = key.split('=')[0], key.split('=')[1]
    strkeys = strkey.split('.')
    print("strkeys = " ,strkeys)
    target = a
    k = ""
    for k in strkeys:
        print(target.keys())
        if k in target.keys():
            prevTarget = target
            target = target[k]
        else:
            print ("Invalid key specified")
            return
    prevTarget[k] = strval


MutateDict(str_key_1)

print(a)

MutateDict(str_key_2)

print(a)

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