updated example, thanks to @leorochael

14-inheritance/strkeydict_dictsub.py

@@ -0,0 +1,93 @@
+"""StrKeyDict always converts non-string keys to `str`
+
+This is a variation of `strkeydict.StrKeyDict` implemented
+as a `dict` built-in subclass (instead of a `UserDict` subclass)
+
+Test for initializer: keys are converted to `str`.
+
+    >>> d = StrKeyDict([(2, 'two'), ('4', 'four')])
+    >>> sorted(d.keys())
+    ['2', '4']
+
+Tests for item retrieval using `d[key]` notation::
+
+    >>> d['2']
+    'two'
+    >>> d[4]
+    'four'
+    >>> d[1]
+    Traceback (most recent call last):
+      ...
+    KeyError: '1'
+
+Tests for item retrieval using `d.get(key)` notation::
+
+    >>> d.get('2')
+    'two'
+    >>> d.get(4)
+    'four'
+    >>> d.get(1, 'N/A')
+    'N/A'
+
+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: cannot unpack non-iterable int object
+
+"""
+
+
+class StrKeyDict(dict):
+
+    def __init__(self, iterable=None, **kwds):
+        super().__init__()
+        self.update(iterable, **kwds)
+
+    def __missing__(self, key):
+        if isinstance(key, str):
+            raise KeyError(key)
+        return self[str(key)]
+
+    def __contains__(self, key):
+        return key in self.keys() or str(key) in self.keys()
+
+    def __setitem__(self, key, item):
+        super().__setitem__(str(key), item)
+
+    def get(self, key, default=None):
+        try:
+            return self[key]
+        except KeyError:
+            return default
+
+    def update(self, iterable=None, **kwds):
+        if iterable is not None:
+            try:  # duck typing FTW!
+                pairs = iterable.items()
+            except AttributeError:
+                pairs = iterable
+            for key, value in pairs:
+                self[key] = value
+        if kwds:
+            self.update(kwds)