MagicAttr

Common errors

• ModuleNotFoundError: No module named 'magicattr'

  cause The `magicattr` library is not installed in the current Python environment.
  fix pip install magicattr

• TypeError: Path must be a string or a list of path segments

  cause The `path` argument passed to `get_at` or `set_at` is neither a string nor a list, which are the only accepted types for defining the navigation path.
  fix Ensure the path argument is a dot-separated string (e.g., 'a.b.0.c') or a list of segments (e.g., ['a', 'b', 0, 'c']).

• KeyError: 'some_key'

  cause During path traversal, `magicattr` encountered a dictionary where a specified key ('some_key' in this example) does not exist, and it propagates the original `KeyError`.
  fix Verify the path string or list against the actual structure of the nested dictionary to ensure all keys exist, or handle the potential `KeyError` with a `try-except` block.

• ImportError: cannot import name 'magicattr' from 'magicattr'

  cause The user is attempting to import the `magicattr` package itself as a named object or function, but the primary functions (`get_at` and `set_at`) are exposed directly from the package, not the package name itself.
  fix Import the specific functions you intend to use, such as `from magicattr import get_at, set_at`.

Warnings

• gotcha MagicAttr's path parsing does not support advanced Python syntax such as slicing (e.g., `list[1:3]`), arbitrary expressions (e.g., `list[0+1]`), function calls (e.g., `list.pop(0)`), or `eval` related constructs within the attribute string. Attempting to use these will result in `NotImplementedError` or `ValueError`.
  Fix: Ensure attribute paths are simple dot-separated or bracket-indexed strings. Perform complex logic outside the `magicattr` call.
• gotcha Unlike standard `getattr`/`setattr` which consistently raise `AttributeError` for missing or invalid attributes, `magicattr` aims to return the underlying exception (e.g., `KeyError` for dicts, `IndexError` for lists) or `None` for missing attributes/indices. This can lead to different error handling patterns than typically expected from Python's built-in attribute access.
  Fix: Inspect the return value carefully for `None` or specific exceptions like `KeyError` or `IndexError` when an attribute might not exist, rather than solely catching `AttributeError`.
• gotcha When using `magicattr.set()` to create new, deeply nested structures (e.g., `magicattr.set(obj, 'new_attr.nested_key', 'value')`), the library automatically infers and creates intermediate `dict` or `list` types as needed. While convenient, this might not always align with expectations if a different custom object type was desired for those intermediate steps.
  Fix: Explicitly initialize intermediate objects with the desired types before using `magicattr.set()` if `dict` or `list` are not appropriate defaults.

Install

• pip install magicattr Install latest version

Imports

• magicattr

  from magicattr import magicattr

Quickstart

Demonstrates getting, setting, and deleting nested attributes using string paths, including auto-creation of intermediate dictionary structures.

from magicattr import magicattr

class Person:
    def __init__(self, name, age, settings=None, friends=None):
        self.name = name
        self.age = age
        self.settings = settings if settings is not None else {}
        self.friends = friends if friends is not None else []

bob = Person("Bob", 30, {'preferences': {'theme': 'dark'}})
jill = Person("Jill", 25, friends=[Person("Jack", 28), Person("Jane", 27)])

# Get a nested attribute
theme = magicattr.get(bob, 'settings.preferences.theme')
print(f"Bob's theme: {theme}")

# Set a nested attribute
magicattr.set(bob, 'age', 32)
print(f"Bob's new age: {bob.age}")

magicattr.set(jill, 'friends[0].age', 29)
print(f"Jill's first friend's new age: {jill.friends[0].age}")

# Delete a nested attribute
magicattr.delete(jill, 'friends[0]')
print(f"Jill's friends after deletion: {[f.name for f in jill.friends] if jill.friends else 'None'}")

# Demonstrate setting a new deeply nested attribute, creating intermediate dicts
magicattr.set(bob, 'address.city', 'New York')
print(f"Bob's city: {bob.address.city}")