docs/library/array: Add docs for dunder methods.

Signed-off-by: Damien George <damien@micropython.org>

docs/library/array.rst

@@ -27,3 +27,55 @@ Classes
 
         Append new elements as contained in *iterable* to the end of
         array, growing it.
+
+    .. method:: __getitem__(index)
+
+        Indexed read of the array, called as ``a[index]`` (where ``a`` is an ``array``).
+        Returns a value if *index* is an ``int`` and an ``array`` if *index* is a slice.
+        Negative indices count from the end and ``IndexError`` is thrown if the index is
+        out of range.
+
+        **Note:** ``__getitem__`` cannot be called directly (``a.__getitem__(index)`` fails) and
+        is not present in ``__dict__``, however ``a[index]`` does work.
+
+    .. method:: __setitem__(index, value)
+
+        Indexed write into the array, called as ``a[index] = value`` (where ``a`` is an ``array``).
+        ``value`` is a single value if *index* is an ``int`` and an ``array`` if *index* is a slice.
+        Negative indices count from the end and ``IndexError`` is thrown if the index is out of range.
+
+        **Note:** ``__setitem__`` cannot be called directly (``a.__setitem__(index, value)`` fails) and
+        is not present in ``__dict__``, however ``a[index] = value`` does work.
+
+    .. method:: __len__()
+
+        Returns the number of items in the array, called as ``len(a)`` (where ``a`` is an ``array``).
+
+        **Note:** ``__len__`` cannot be called directly (``a.__len__()`` fails) and the
+        method is not present in ``__dict__``, however ``len(a)`` does work.
+
+    .. method:: __add__(other)
+
+        Return a new ``array`` that is the concatenation of the array with *other*, called as
+        ``a + other`` (where ``a`` and *other* are both ``arrays``).
+
+        **Note:** ``__add__`` cannot be called directly (``a.__add__(other)`` fails) and
+        is not present in ``__dict__``, however ``a + other`` does work.
+
+    .. method:: __iadd__(other)
+
+        Concatenates the array with *other* in-place, called as ``a += other`` (where ``a`` and *other*
+        are both ``arrays``).  Equivalent to ``extend(other)``.
+
+        **Note:** ``__iadd__`` cannot be called directly (``a.__iadd__(other)`` fails) and
+        is not present in ``__dict__``, however ``a += other`` does work.
+
+    .. method:: __repr__()
+
+        Returns the string representation of the array, called as ``str(a)`` or ``repr(a)```
+        (where ``a`` is an ``array``).  Returns the string ``"array(<type>, [<elements>])"``,
+        where ``<type>`` is the type code letter for the array and ``<elements>`` is a comma
+        seperated list of the elements of the array.
+
+        **Note:** ``__repr__`` cannot be called directly (``a.__repr__()`` fails) and
+        is not present in ``__dict__``, however ``str(a)`` and ``repr(a)`` both work.