"""StrKeyDict always converts non-string keys to `str`

Tests for item retrieval using `d[key]` notation::

    >>> d = StrKeyDict([('2', 'two'), ('4', 'four')])
    >>> d['2']
    'two'
    >>> d[4]
    'four'
    >>> d[1]
    Traceback (most recent call last):
      ...
    KeyError: '1'

Tests for the `in` operator::

    >>> 2 in d
    True
    >>> 1 in d
    False

Test for item assignment using non-string key::

    >>> d[0] = 'zero'
    >>> d['0']
    'zero'

Tests for update using a `dict` or a sequence of pairs::

    >>> d.update({6:'six', '8':'eight'})
    >>> sorted(d.keys())
    ['0', '2', '4', '6', '8']
    >>> d.update([(10, 'ten'), ('12', 'twelve')])
    >>> sorted(d.keys())
    ['0', '10', '12', '2', '4', '6', '8']
    >>> d.update([1, 3, 5])
    Traceback (most recent call last):
      ...
    TypeError: 'int' object is not iterable

"""
# BEGIN STRKEYDICT

import collections
import collections.abc


class StrKeyDict(collections.UserDict):  # <1>

    def __init__(self, args, normalize=str, **kwargs):
        super().__init__(self, *args, **kwargs)
        self.normalize = normalize

    def __missing__(self, key):  # <2>
        if self.normalize(key) == key:
            raise KeyError(key)
        return self[self.normalize(key)]

    def __contains__(self, key):
        return self.normalize(key) in self.data  # <3>

    def __setitem__(self, key, item):
        self.data[self.normalize(key)] = item   # <4>

    def update(self, iterable=None, **kwds):
        if iterable is not None:
            if isinstance(iterable, collections.abc.Mapping):  # <5>
                pairs = iterable.items()
            else:
                pairs = ((k, v) for k, v in iterable)  # <6>
            for key, value in pairs:
                self[key] = value  # <7>
        if kwds:
            self.update(kwds)  # <8>

# END STRKEYDICT