📝 Update dict type

Author: veit

docs/types/dicts.rst

@@ -1,45 +1,89 @@
 Dictionaries
 ============
 
-Python’s built-in dictionary data type provides associative array functionality
-implemented using hash tables. The built-in ``len`` function returns the number
-of key-value pairs in a dictionary. The ``del`` statement can be used to delete
-a key-value pair. As with :doc:`sequences-sets/lists` , several dictionary
-methods (:py:meth:`clear <dict.clear>`, :py:meth:`copy <dict.copy>`,
-:py:meth:`get <dict.get>`, :py:meth:`items <dict.items>`, :py:meth:`keys
-<dict.keys>`, :py:meth:`update <dict.update>` and :py:meth:`values
-<dict.values>`) are available.
-
-.. code-block:: pycon
-
-    >>> x = {1: "eins", 2: "zwei"}
-    >>> x[3] = "drei"
-    >>> x["viertes"] = "vier"
-    >>> list(x.keys())
-    [1, 2, 3, 'viertes']
-    >>> x[1]
-    'eins'
-    >>> x.get(1, "nicht vorhanden")
-    'eins'
-    >>> x.get(5, "nicht vorhanden")
-    'nicht vorhanden'
-
-Keys must be of immutable type, including :doc:`numbers/index`,
-:doc:`strings/index` and :doc:`sequences-sets/tuples`.
+Dictionaries consist of key-value pairs. Keys must be of invariant type,
+including numbers, :doc:`strings/index` and :doc:`sequences-sets/tuples`.
 
 .. warning::
    Even if you can use different key types in a dictionary, you should avoid
-   this, as it not only makes it more difficult to read, but also sorting is
-   also made more difficult.
+   doing so, as this not only makes it more difficult to read, but also to sort.
 
 Values can be any type of object, including mutable types such as
-:doc:`sequences-sets/lists` and :doc:`dicts`. If you try to access the value of
-a key that is not in the dictionary, a ``KeyError`` exception is thrown. To
-avoid this error, the dictionary method ``get`` optionally returns a custom
-value if a key is not contained in a dictionary.
+:doc:`sequences-sets/lists` and :doc:`dicts`.
+
+.. code-block:: pycon
+
+   >>> dict = {
+   ...     "2022-01-31": -0.751442,
+   ...     "2022-02-01": 0.816935,
+   ...     "2022-02-02": -0.272546,
+   ... }
+   >>> dict["2022-02-03"] = -0.268295
+
+If you try to access the value of a key that is not contained in the dictionary,
+a ``KeyError`` exception is thrown. To avoid this error, the dictionary method
+``get`` optionally returns a user-defined value if a key is not contained in a
+dictionary.
+
+.. code-block:: pycon
+
+   >>> dict["2022-02-03"]
+   -0.268295
+   >>> dict["2022-02-04"]
+   Traceback (most recent call last):
+     File "<python-input-15>", line 1, in <module>
+       dict["2022-02-04"]
+       ~~~~^^^^^^^^^^^^^^
+   KeyError: '2022-02-04'
+   >>> dict.get("2022-02-03", "Messwert nicht vorhanden")
+   -0.268295
+   >>> dict.get("2022-02-04", "Messwert nicht vorhanden")
+   'Messwert nicht vorhanden'
+
+Other Dict methods
+------------------
+
+The :func:`len` function built into Dicts returns the number of key-value pairs.
+The ``del`` statement can be used to delete a key-value pair. As with
+:doc:`sequences-sets/lists`, several dictionary methods ((:py:meth:`clear
+<dict.clear>`, :py:meth:`copy <dict.copy>`, :py:meth:`get <dict.get>`,
+:py:meth:`items <dict.items>`, :py:meth:`keys <dict.keys>`, :py:meth:`update
+<dict.update>` and :py:meth:`values <dict.values>`) are available.
+
+The :py:meth:`keys <dict.keys>`, :py:meth:`values <dict.values>` and
+:py:meth:`items <dict.items>` methods do not return lists, but dictionary view
+objects that behave like sequences, but are updated dynamically when the
+dictionary changes. For this reason, you must use the :func:`list` function so
+that they become a list in these examples:
+
+.. code-block:: pycon
+
+   >>> list(dict.keys())
+   ['2022-01-31', '2022-02-01', '2022-02-02', '2022-02-03']
+
+As of Python 3.6, dictionaries retain the order in which the keys were created,
+and they are also returned in this order with  :py:meth:`keys <dict.keys>`.
+
+Merging dictionaries
+~~~~~~~~~~~~~~~~~~~~
+
+You can use the :py:meth:`dict.update` method to merge two dictionaries into a
+single dictionary:
+
+.. code-block:: pycon
+
+   >>> titles = {7.0: "Data Types", 7.1: "Lists", 7.2: "Tuples"}
+   >>> new_titles = {7.0: "Data types", 7.3: "Sets"}
+   >>> titles.update(new_titles)
+   >>> titles
+   {7.0: 'Data types', 7.1: 'Lists', 7.2: 'Tuples', 7.3: 'Sets'}
+
+.. note::
+   The order of the operands is important, as ``7.0`` is duplicated and the
+   value of the last key overwrites the previous one.
 
 ``setdefault``
---------------
+~~~~~~~~~~~~~~
 
 :py:meth:`setdefault <dict.setdefault>` can be used to provide counters for the
 keys of a dict, for example:
@@ -65,84 +109,31 @@ keys of a dict, for example:
       >>> collections.Counter(titles)
       Counter({'Lists': 2, 'Data types': 1, 'Sets': 1})
 
-Merging dictionaries
---------------------
-
-You can merge two dictionaries into a single dictionary using the
-:py:meth:`dict.update` method:
-
-.. code-block:: pycon
-
-   >>> titles = {7.0: "Data Types", 7.1: "Lists", 7.2: "Tuples"}
-   >>> new_titles = {7.0: "Data types", 7.3: "Sets"}
-   >>> titles.update(new_titles)
-   >>> titles
-   {7.0: 'Data types', 7.1: 'Lists', 7.2: 'Tuples', 7.3: 'Sets'}
-
-.. note::
-   The order of the operands is important, as ``7.0`` is duplicated and the
-   value of the last key overwrites the previous one.
-
 Extensions
 ----------
 
 `python-benedict <https://github.com/fabiocaccamo/python-benedict>`_
     ``dict`` subclass with keylist/keypath/keyattr support and I/O shortcuts.
 :doc:`pandas <Python4DataScience:workspace/pandas/python-data-structures>`
-    can convert Dicts into Series and DataFrames.
+    can convert dicts into series and DataFrames.
 
 Checks
 ------
 
-* Suppose you have the two dictionaries ``x = {"a":1, "b":2, "c":3, "d":4}`` and
-  ``y = {"a":5, "e":6, "f":7}``. What would be the content of ``x`` after the
-  following code snippets have been executed?
+* Suppose you have the two dictionaries ``x = {"a": 1, "b": 2, "c": 3, "d": 4}``
+  and ``y = {"a": 5, "e": 6, "f": 7}``. What would be the content of ``x`` after
+  the following code snippets have been executed?
 
   .. code-block:: pycon
 
      >>> del x["b"]
      >>> z = x.setdefault("e", 8)
      >>> x.update(y)
 
-  .. code-block:: pycon
-
-     >>> x = {"a": 1, "b": 2, "c": 3, "d": 4}
-     >>> y = {"a": 5, "e": 6, "f": 7}
-     >>> del x["b"]
-     >>> z = x.setdefault("e", 8)
-     >>> x.update(y)
-     >>> x
-     {'a': 5, 'c': 3, 'd': 4, 'e': 6, 'f': 7}
-
-* Which of the following expressions can be a key of a dictionary:  ``1``;
-  ``"Veit"``; ``("Veit", [1])``; ``[("Veit", [1])]``; ``["Veit"]``; ``("Veit",
-  "Tim", "Monique")``
-
-  .. code-block:: pycon
-
-     >>> d = {}
-     >>> d[1] = None
-     >>> d["Veit"] = None
-     >>> d[("Veit", [1])]
-     Traceback (most recent call last):
-       File "<stdin>", line 1, in <module>
-     TypeError: unhashable type: 'list'
-     >>> d[["Veit"]] = None
-     Traceback (most recent call last):
-       File "<stdin>", line 1, in <module>
-     TypeError: unhashable type: 'list'
-     >>> d[("Veit", "Tim", "Monique")] = None
-
-* You can use a :doc:`Dictionary </types/dicts>` like a spreadsheet table by
-  using :doc:`/types/sequences-sets/tuples` as key row and column values. Write
-  sample code to add and retrieve values.
-
-  .. code-block:: pycon
+* Which of the following expressions can be a key of a dictionary?
+  ``1``; ``"Veit"``; ``("Veit", [1])``; ``[("Veit", [1])]``; ``["Veit"]``;
+  ``("Veit", "Tim", "Monique")``
 
-     >>> sheet = {}
-     >>> sheet[("A", 0)] = 1
-     >>> sheet[("A", 1)] = 2
-     >>> sheet[("B", 0)] = 3
-     >>> sheet[("B", 1)] = 4
-     >>> print(sheet[("A", 1)])
-     2
+* You can use a :doc:`dictionary </types/dicts>`  and use it like a spreadsheet
+  sheet by using :doc:`tuples </types/sequences-sets/tuples>` as key row and
+  column values. Write sample code to add and retrieve values.