Python deep_get

deep_get.py

# coding=utf-8
from __future__ import unicode_literals
import collections

_default_stub = object()


def to_unicode(s):
    if isinstance(s, str):
        return unicode(s, 'utf8')
    return unicode(s)


def deep_get(obj, path, default=_default_stub, separator='.'):
    """Get arbitrarily nested attribute or item value.

    Args:
        obj: Object to search in.
        path (str, hashable, iterable of hashables): Arbitrarily nested path in obj hierarchy.
        default: Default value. When provided it is returned if the path doesn't exist.
            Otherwise the call raises a LookupError.
        separator: String to split path by.

    Returns:
        Value at path.

    Raises:
        LookupError: If object at path doesn't exist.

    Examples:
        >>> deep_get({'a': 1}, 'a')
        1

        >>> deep_get({'a': 1}, 'b')
        Traceback (most recent call last):
            ...
        LookupError: {u'a': 1} has no element at 'b'

        >>> deep_get(['a', 'b', 'c'], -1)
        u'c'

        >>> deep_get({'a': [{'b': [1, 2, 3]}, 'some string']}, 'a.0.b')
        [1, 2, 3]

        >>> class A(object):
        ...     def __init__(self):
        ...         self.x = self
        ...         self.y = {'a': 10}
        ...
        >>> deep_get(A(), 'x.x.x.x.x.x.y.a')
        10

        >>> deep_get({'a.b': {'c': 1}}, 'a.b.c')
        Traceback (most recent call last):
            ...
        LookupError: {u'a.b': {u'c': 1}} has no element at 'a'

        >>> deep_get({'a.b': {'Привет': 1}}, ['a.b', 'Привет'])
        1

        >>> deep_get({'a.b': {'Привет': 1}}, 'a.b/Привет', separator='/')
        1
    """
    if isinstance(path, basestring):
        attributes = path.split(separator)
    elif isinstance(path, collections.Iterable):
        attributes = path
    else:
        attributes = [path]

    getattr_errors = (AttributeError, TypeError, UnicodeEncodeError)
    getitem_errors = (TypeError, IndexError, KeyError)
    conversion_errors = (UnicodeEncodeError, ValueError)

    lookups = [
        (getattr, getattr_errors),
        (lambda o, i: o[i], getitem_errors),
        (lambda o, i: o[int(i)], getitem_errors + conversion_errors),
    ]

    try:
        for attr in attributes:
            for lookup, errors in lookups:
                try:
                    obj = lookup(obj, attr)
                    break
                except errors:
                    pass
            else:
                msg = "{} has no element at '{}'".format(to_unicode(obj), to_unicode(attr))
                raise LookupError(msg.encode('utf8'))
    except Exception:
        if _default_stub != default:
            return default
        raise

    return obj