How to set attribute on an object given a dotted path?

Question

Given an object that can be a nested structure of dict-like or array-like objects. What is the pythonic way to set a value on that object given a dotted path as a string?

Example:

obj = [
    {'a': [1, 2]},
    {'b': {
        'c': [3, 4],
    }},
]

path = '1.b.c.0'

# operation that sets a value at the given path, e.g.
obj[path] = 5

# or
set_value(obj, path, 5)

The above call/assignment should replace the 3 in the example with a 5.

Note: The path can contain list indices as well as keys. Every level of the object can be an array or a dict or something that behaves like that.

The solution should be roughly like what the npm package object-path does in javascript.

Answer 1

A non-recursive version, which also works for numeric dictionary keys:

from collections.abc import MutableMapping

def set_value_at_path(obj, path, value):
    *parts, last = path.split('.')

    for part in parts:
        if isinstance(obj, MutableMapping):
            obj = obj[part]
        else:
            obj = obj[int(part)]

    if isinstance(obj, MutableMapping):
        obj[last] = value
    else:
        obj[int(last)] = value

Answer 2

Sounds like a job for recursion and str.partition:

def set_value(obj, path, val):
    first, sep, rest = path.partition(".")
    if first.isnumeric():
        first = int(first)
    if rest:
        new_obj = obj[first]
        set_value(new_obj, rest, val)
    else:
        obj[first] = val

Because 1 is not the same as "1", I'm making a compromise here: If something looks like a number, it's treated as a number.

You could get this to behave on custom objects, but not really on builtin types without awful hackery, because Python doesn't have an equivalent to object.prototype.