Module unitexpr.unit_symbol

Provides UnitSymbol an immutable class representing base unit symbols.

None

View Source

"""

Provides `UnitSymbol` an immutable class representing base unit symbols.

"""

from typing import NamedTuple

import re

class UnitSymbol(

    NamedTuple("_UnitSymbol", symbol=str, name=str, quantity=str),

):

    """

    Immutable class inheriting from `NamedTuple` representing a

    base unit symbol with fields:

    * symbol: The symbol displayed in unit expressions. Should be a valid

      Python identifier.

    * name: The unit name.

    * quantity: The physical quantity represented by the unit.

    ``` python

    m = UnitSymbol('m', 'meter', 'length')

    s = UnitSymbol(symbol='s', name='second', quantity='time')

    ```

    """

    __slots__ = ()

    __reg_expr = "^[A-Za-z_][A-Za-z0-9_]*"

    def __new__(cls, symbol: str, name: str, quantity: str):

        if not UnitSymbol.is_valid_symbol(symbol):

            raise ValueError(

                f"Symbol {type(symbol)}:{symbol} is not a valid identifier."

            )

        return super().__new__(cls, symbol, name, quantity)

    @classmethod

    def is_valid_symbol(cls, value: str) -> bool:

        """

        Returns `True` if `value` matches the regular expression:

        '^[A-Za-z_][A-Za-z0-9_]*'

        """

        if not isinstance(value, str):

            return False

        if re.fullmatch(UnitSymbol.__reg_expr, value) is None:

            return False

        return True

Classes

UnitSymbol

class UnitSymbol(
    /,
    *args,
    **kwargs
)

View Source

class UnitSymbol(

    NamedTuple("_UnitSymbol", symbol=str, name=str, quantity=str),

):

    """

    Immutable class inheriting from `NamedTuple` representing a

    base unit symbol with fields:

    * symbol: The symbol displayed in unit expressions. Should be a valid

      Python identifier.

    * name: The unit name.

    * quantity: The physical quantity represented by the unit.

    ``` python

    m = UnitSymbol('m', 'meter', 'length')

    s = UnitSymbol(symbol='s', name='second', quantity='time')

    ```

    """

    __slots__ = ()

    __reg_expr = "^[A-Za-z_][A-Za-z0-9_]*"

    def __new__(cls, symbol: str, name: str, quantity: str):

        if not UnitSymbol.is_valid_symbol(symbol):

            raise ValueError(

                f"Symbol {type(symbol)}:{symbol} is not a valid identifier."

            )

        return super().__new__(cls, symbol, name, quantity)

    @classmethod

    def is_valid_symbol(cls, value: str) -> bool:

        """

        Returns `True` if `value` matches the regular expression:

        '^[A-Za-z_][A-Za-z0-9_]*'

        """

        if not isinstance(value, str):

            return False

        if re.fullmatch(UnitSymbol.__reg_expr, value) is None:

            return False

        return True

---

Ancestors (in MRO)

• unitexpr.unit_symbol._UnitSymbol
• builtins.tuple

Class variables

name

quantity

symbol

Static methods

is_valid_symbol

def is_valid_symbol(
    value: str
) -> bool

Returns True if value matches the regular expression:

'^[A-Za-z_][A-Za-z0-9_]*'

View Source

    @classmethod

    def is_valid_symbol(cls, value: str) -> bool:

        """

        Returns `True` if `value` matches the regular expression:

        '^[A-Za-z_][A-Za-z0-9_]*'

        """

        if not isinstance(value, str):

            return False

        if re.fullmatch(UnitSymbol.__reg_expr, value) is None:

            return False

        return True

Methods

count

def count(
    self,
    value,
    /
)

Return number of occurrences of value.

index

def index(
    self,
    value,
    start=0,
    stop=9223372036854775807,
    /
)

Return first index of value.

Raises ValueError if the value is not present.