1) Separate the cpp object from the expression object. A separate object or function should combine them.

2) Re-organize ther directory structre as suggested below. 

3) List of functionalities

def isNumeric(obj)
def process_numeric(expression):
class SelectedExpressionsIterator: iterator for catalogs

Expression:
Access:
    def __iter__(self):
Inspection:
    def check_panel_trajectory(self):
    def check_draws(self):
    def check_rv(self):
    def getStatusIdManager(self):
    def requiresDraws(self):
    def getClassName(self):
    def embedExpression(self, t):
    def countPanelTrajectoryExpressions(self):
    def audit(self, database=None):

Modification:
    def rename_elementary(self, names, prefix=None, suffix=None):
    def fix_betas(self, beta_values, prefix=None, suffix=None):
    def change_init_values(self, betas):


List of elements:
    def get_beta_values(self):
    def set_of_elementary_expression(self, the_type):
    def dict_of_elementary_expression(self, the_type):
    def getElementaryExpression(self, name):
    def getClassName(self):
    def getSignature(self):
    def dict_of_catalogs(self, ignore_synchronized=False):
    def contains_catalog(self, name):
    def set_of_multiple_expressions(self):
    def get_id(self):
    def get_children(self):

Specific to catalog 
    def set_central_controller(self, the_central_controller=None):
    def reset_expression_selection(self):
    def configure_catalogs(self, configuration):
    def get_all_controllers(self):
    def number_of_multiple_expressions(self):
    def set_of_configurations(self):
    def current_configuration(self):
    def select_expression(self, controller_name, index):

Preparation:
    def prepare(self, database, numberOfDraws):
This is where the cython cpp object should be linked
    def setIdManager(self, id_manager):

Operator overloading... many...

Usage:
    def createFunction(
    def getValue_c(
    def getValueAndDerivatives(


Organizing a project with multiple classes and functionalities can be challenging, but with a modular approach, it becomes more manageable. Here's a suggested organization for your arithmetic expression project:

1. **Directory Structure**: 
    - Organize the classes into separate files based on their responsibilities and group related files into directories (packages).
  
```
arithmetic_expressions/
│
├── __init__.py
│
├── base/
│   ├── __init__.py
│   └── expression.py   # Contains the Expression base class
│
├── operators/
│   ├── __init__.py
│   ├── unary.py        # Contains UnaryOperator and its derivatives
│   ├── binary.py       # Contains BinaryOperator and its derivatives
│   └── nary.py         # Contains NaryOperator and its derivatives
│
└── utils/
    └── __init__.py
    └── deepcopy_utils.py  # Utility functions related to deep copying, if any
```

2. **Use of `__init__.py`**:
    - In each directory, there's an `__init__.py` file, which makes a directory a Python package. This file can also be used to facilitate easier imports. For instance, inside `operators/__init__.py`, you could have:
      ```python
      from .unary import Negative, ...
      from .binary import Addition, Subtraction, ...
      from .nary import Sum, ...
      ```

3. **Imports**:
    - With the above structure, you can easily import classes in your main code or other modules using statements like:
      ```python
      from arithmetic_expressions.operators import Addition, Negative, Sum
      ```

4. **Documentation**:
    - Document each file at the beginning to describe its purpose and main classes/functions. This makes it easier for others (and your future self) to understand the code.
  
5. **Tests**:
    - For a more comprehensive project structure, consider adding a separate `tests/` directory at the root level. Inside, you can have test files corresponding to each module, e.g., `test_unary.py`, `test_binary.py`, etc. 

6. **README**:
    - Include a `README.md` or `README.rst` file at the root of your project to provide an overview, setup instructions, and examples of how to use the code.

7. **Extensions**:
    - If in the future you decide to add more functionalities or types of operators, you can simply create a new file under the appropriate directory, keeping the project modular and organized.

By organizing your project in a modular manner, you make it scalable, maintainable, and more understandable for both yourself and others who might work on or use your code.
