recursion - Convert python decimal to string in deeply nested and unpredictable list

Question

I am trying to loop through every value in a deeply nested/mixed list and convert any Decimal instances to string so that I can store them in mongo.

My attempt at recursion reached the max depth. I would like to solve this iteratively or in a performant manner.

This doesn't seem to work but is my latest attempt:

def convert_decimals(root_obj):
    objs_to_convert = [root_obj]

    while objs_to_convert:
        obj = objs_to_convert.pop(0)
        for k, v in enumerate(obj):

            if len(v):
                objs_to_convert.append(v)
            elif isinstance(v, Decimal):
                obj[k] = str(v)

Sample Input:

[
    {
        'Payments': {
            'Payment': Decimal('495.64'),
            'IsCapped': True,
            'OtherFees': Decimal('0'),
            'CapCostTotal': Decimal('27900'),
            'Name': 'TestData',
            'Program': {
                'ProgramName': u'AST',
                'Description': None
            },
            'Rate': Decimal('0.0254'),
            'APR': Decimal('2.54'),
            'AppliedIds': [

            ],
            'Tax': Decimal('0')
        }
    }
]

After conversion, the decimal instances should be strings

Answer 1

To convert Decimal during json.dump() using default parameter:

import json
import sys
from decimal import Decimal

def default(obj):
    if isinstance(obj, Decimal):
        return str(obj)
    else:
        raise TypeError(obj)

# convert during dump
json.dump(data, sys.stdout, indent=2, default=default)

To modify data inplace:

import json
import sys
from collections import MutableMapping, MutableSequence
from decimal import Decimal

def convert_decimal(json_data):
    stack = [json_data]
    while stack:
        json_data = stack.pop()
        if isinstance(json_data, MutableMapping): # json object
            it = json_data.items()
        elif isinstance(json_data, MutableSequence): # json array
            it = enumerate(json_data)
        else: # scalar data
            continue

        for k, v in it:
            if isinstance(v, Decimal):
                json_data[k] = str(v)
            else:
                stack.append(v)


# convert inplace
convert_decimal(data)
json.dump(data, sys.stdout, indent=2)

Both scripts produce the same output:

[
  {
    "Payments": {
      "OtherFees": "0", 
      "APR": "2.54", 
      "Rate": "0.0254", 
      "IsCapped": true, 
      "Name": "TestData", 
      "Program": {
        "Description": null, 
        "ProgramName": "AST"
      }, 
      "AppliedIds": [], 
      "CapCostTotal": "27900", 
      "Tax": "0", 
      "Payment": "495.64"
    }
  }
]

You could simplify convert_decimal() if you use a generic get_items() function:

def convert_decimal(json_data):
    stack = [json_data]
    while stack:
        json_data = stack.pop()
        for k, v in get_items(json_data):
            if isinstance(v, Decimal):
                json_data[k] = str(v)
            else:
                stack.append(v)