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constant.py: Custom Constant Handling
A custom class for handling constant values and enforcing naming conventions.
   
Class Definition
The `_const` class defines a mechanism for custom constant handling, ensuring that constant values and their names follow specific rules.
   
   
Implementation Details:
   
  
    
Exception Handling - Two specific exceptions are defined:
    
     
      
      
ConstError: Raised when attempting to reassign a constant value.
      
      
ConstCaseError: Raised when constant name does not conform to specified naming conventions.
    
     
  
    
Method Overloading via __setattr__ - Custom behavior for attribute assignment:
    
     
      
      
If the attribute already exists in the instance's dictionary, it raises a ConstError to prevent reassignment.
      
      
All constant names must be uppercase letters; lowercase names will throw a ConstCaseError.
      
      
The attribute is then set in the instance's dictionary for future reference.
    
     
   
   
Demostration: Usage in Practice
Example: constant.py
Here's how the constant class is implemented in the constant.py file:
from constant import const
class _const:
    # Custom exception definitions
    class ConstError(PermissionError):
        pass
    class ConstCaseError(ConstError):
        pass
    
    def __setattr__(self, name, value):
        if name in self.__dict__:
            raise self.ConstError("Cannot assign value to constant {0}".format(name))
        if not name.isupper():
            raise self.ConstCaseError("const name {0} is not all uppercase".format(name))
        setattr(self, name, value)
        
const = _const()
const.PI = 3.14
Example Usage: demo.py
Here's how the constant values are used in a separate application (demo.py):
from constant import const
print(const.PI)  # Outputs: 3.14
   
This implementation ensures that constant values remain immutable and Follow consistent naming conventions, which is essential for maintaining reliable codebase.