Add support for dict.items (pyccel#2073)

Make `Iterable` into a super-class instead of a storage class. Functions
that can be used in an iterable context must inherit from this class and
define useful methods. The method `get_python_iterable_item` must be
defined. If the iterable can be converted to a range the methods
`get_range` and `get_assign_targets` must also be defined. Organising
iterables via inheritance instead of storing the object in the
`Iterable` class avoids problems with circular includes as the low-level
`Iterable` object no longer depends on a large number of other ast
modules.

The new setup is used to add support for `dict.items`.

**Commit Summary**
- Add an `Iterable` sub-class describing `dict.items`.
- Change method names in `Iterable` sub-classes
- Remove unnecessary methods `length` and `__getitem__` in `Iterable`
sub-classes
- Add `Iterable` as a super class of objects that can be iterated over.
- Add a `prefer_inhomogeneous` argument to `PythonTuple` which allows
the developer to force the creation of an inhomogeneous tuple (e.g. for
the target when iterating over an enumerate of integers).
- Add a `VariableIterator` class to represent the `iter()` function that
is called implicitly in a for loop
- Move `Iterable` class from `ast.core` to `ast.internals`
- Remove unnecessary line for `Iterable` in sympy_helper.
- Save the `For` target as a tuple after the semantic stage
- Fix insertion of an inhomogeneous tuple into a loop scope.
- Create `_get_for_iterators` function to unify handling of iterators in
FunctionalFor/GeneratorExpressions/For loops
- Add tests

Author: EmilyBourne

CHANGELOG.md

@@ -42,6 +42,7 @@ All notable changes to this project will be documented in this file.
 -   #1918 : Add support for set method `clear()`.
 -   #1918 : Add support for set method `copy()`.
 -   #1753 : Add support for set method `union()`.
+-   #1884 : Add support for dict method `items()`.
 -   #1936 : Add missing C output for inline decorator example in documentation
 -   #1937 : Optimise `pyccel.ast.basic.PyccelAstNode.substitute` method.
 -   #1544 : Add support for `typing.TypeAlias`.
@@ -110,6 +111,7 @@ All notable changes to this project will be documented in this file.
 -   \[INTERNALS\] Stop using ndarrays as an intermediate step to call Fortran code.
 -   \[INTERNALS\] Stop using ndarrays as an intermediate step to return arrays from Fortran code.
 -   \[INTERNALS\] Unify the strategy for handling additional imports in the printing stage for different languages.
+-   \[INTERNALS\] Make `Iterable` into a super-class instead of a storage class.
 
 ### Deprecated
 

docs/builtin-functions.md

@@ -123,7 +123,7 @@ Python contains a limited number of builtin functions defined [here](https://doc
 | `clear` | Python-only |
 | `copy` | Python-only |
 | `get` | Python-only |
-| `items` | No |
+| `items` | **Yes** |
 | `keys` | No |
 | `pop` | Python-only |
 | `popitem` | Python-only |

pyccel/ast/builtin_methods/dict_methods.py

@@ -10,13 +10,15 @@
 This module contains objects which describe these methods within Pyccel's AST.
 """
 
-from pyccel.ast.datatypes import InhomogeneousTupleType, VoidType
-from pyccel.ast.internals import PyccelFunction
+from pyccel.ast.datatypes import InhomogeneousTupleType, VoidType, SymbolicType
+from pyccel.ast.internals import PyccelFunction, Iterable
+from pyccel.ast.variable  import IndexedElement
 
 
 __all__ = ('DictClear',
            'DictCopy',
            'DictGet',
+           'DictItems',
            'DictMethod',
            'DictPop',
            'DictPopitem',
@@ -260,7 +262,6 @@ def __init__(self, dict_obj):
         super().__init__(dict_obj)
 
 #==============================================================================
-
 class DictCopy(DictMethod):
     """
     Represents a call to the .copy() method.
@@ -280,3 +281,49 @@ def __init__(self, dict_obj):
         dict_type = dict_obj.class_type
         self._class_type = dict_type
         super().__init__(dict_obj)
+
+#==============================================================================
+class DictItems(Iterable):
+    """
+    Represents a call to the .items() method.
+
+    Represents a call to the .items() method which iterates over a dictionary.
+
+    Parameters
+    ----------
+    dict_obj : TypedAstNode
+        The object from which the method is called.
+    """
+    __slots__ = ('_dict_obj',)
+    _attribute_nodes = Iterable._attribute_nodes + ("_dict_obj",)
+    _shape = None
+    _class_type = SymbolicType()
+    name = 'items'
+
+    def __init__(self, dict_obj):
+        self._dict_obj = dict_obj
+        super().__init__(1)
+
+    @property
+    def variable(self):
+        """
+        Get the object representing the dict.
+
+        Get the object representing the dict.
+        """
+        return self._dict_obj
+
+    def get_python_iterable_item(self):
+        """
+        Get the item of the iterable that will be saved to the loop targets.
+
+        Returns two objects that could be a key and a value of the dictionary.
+        These elements are used to determine the types of the loop targets.
+
+        Returns
+        -------
+        list[TypedAstNode]
+            A list of objects that should be assigned to variables.
+        """
+        item = DictPopitem(self._dict_obj)
+        return [IndexedElement(item, 0), IndexedElement(item, 1)]