Data Validation

validation_demo.py

# SETUP IN utils.py

class NumParse(Enum):
    VAL = 1  # Valid number
    INV = 2  # Invalid number format
    NEG = 3  # Negative value
    ZER = 4  # Zero value
    EXC = 5  # Exceeds maximum value defined in config

    def __eq__(self, other: str):
        return self.name == other
        
        
def val_float(
    val: Any, nn: bool = True, nz: bool = False, ignore_max: bool = False
) -> tuple[NumParse, float | None]:
    """Helper function to validate user input is a float

    This is literally just to remove repetitive try/except blocks being
    repeated over and over when validating user input forms. It can additionally
    refuse negative numbers, and a ceiling on values is created in the App
    Config to prevent excessively large values.

    Parameters
    ----------
    val : Any
        The value to be tested
    nn : bool
        Stands for non-negative. If True, negative values will be considered
        invalid
    nz : bool
        Stands for non-zero. If True, zero values will be considered invalid
    ignore_max : bool
        Whether to ignore the config-defined maximum value

    Returns
    -------
    tuple[NumParse, float | None]
        An enum of the parsing outcome and, if successful, the parsed value
    """
    try:
        val = float(val)
    except (TypeError, ValueError, OverflowError):
        return NumParse(2), None

    if val < 0 and nn:
        return NumParse(3), None
    elif val == 0 and nz:
        return NumParse(4), None

    if not ignore_max:
        if abs(val) > current_app.config["MAX_NUMBER"]:
            return NumParse(5), None

    return NumParse(1), val
    
   
   # APPLICATION
   from utils import NumpParse as NP
   from utils import val_float

   v, qty = val_float(qty, nz=True) # qty here is from the frontend
   if v is not NP.VAL:
        match v:
            case NP.INV:
                return False, _("Quantity not recognised")
            case NP.NEG | NP.ZER:
                return False, _("Quantity must be positive")
            case NP.EXC:
                return False, _("Maximum quantity exceeded")
            case z:  # noqa: F841
                return False, _("Unknown error occurred")