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types - Common data types

Overview

::: firebird.base.types options: members: false

Exceptions

::: firebird.base.types.Error

Singletons

Singleton is a pattern that restricts the instantiation of a class to one "single" instance. This is useful when exactly one object is needed to coordinate actions across the system.

Common uses:

  • The abstract factory, factory method, builder, and prototype patterns can use singletons in their implementation.

  • Facade objects are often singletons because only one facade object is required.

  • State objects are often singletons.

  • Singletons are often preferred to global variables because:

    • They do not pollute the global namespace with unnecessary variables.
    • They permit lazy allocation and initialization.

To create your own singletons, use [Singleton][firebird.base.types.Singleton] as the base class.

!!! example python >>> class MySingleton(Singleton): ... "Description" ... ... ... >>> obj1 = MySingleton() >>> obj2 = MySingleton() >>> obj1 is obj2 True

::: firebird.base.types.Singleton

Sentinels

The Sentinel Object pattern is a standard Pythonic approach that’s used both in the Standard Library and beyond. The pattern most often uses Python’s built-in None object, but in situations where None might be a useful value, a unique sentinel object() can be used instead to indicate missing or unspecified data, or other specific condition.

However, the plain object() sentinel has not very useful str and repr values. The [Sentinel][firebird.base.types.Sentinel] class provides named sentinels, with meaningful str and repr.

::: firebird.base.types.Sentinel

Predefined sentinels

::: firebird.base.types.DEFAULT

::: firebird.base.types.INFINITY

::: firebird.base.types.UNLIMITED

::: firebird.base.types.UNKNOWN

::: firebird.base.types.NOT_FOUND

::: firebird.base.types.UNDEFINED

::: firebird.base.types.ANY

::: firebird.base.types.ALL

::: firebird.base.types.SUSPEND

::: firebird.base.types.RESUME

::: firebird.base.types.STOP

Distinct objects

Some complex data structures or data processing algorithms require unique object identification (ie object identity). In Python, an object identity is defined internally as unique instance identity that is not suitable for complex objects whose identity is derived from content.

The [Distinct][firebird.base.types.Distinct] abstract base class is intended as a unified solution to these needs.

!!! seealso module [firebird.base.collections][]

::: firebird.base.types.Distinct

::: firebird.base.types.CachedDistinct

Enums

::: firebird.base.types.ByteOrder

::: firebird.base.types.ZMQTransport

::: firebird.base.types.ZMQDomain

Custom string types

Some string values have unified structure and carry specific information (like network address or database connection string). Typical repeating operation with these values are validation and parsing. It makes sense to put these operations under one roof. One such approach uses custom descendants of builtin str type.

!!! caution Custom string types have an inherent weakness. They support all inherited string methods, but any method that returns string value return a base str type, not the descendant class type. That same apply when you assign strings to variables that should be of custom string type.

!!! tip
    Module [firebird.base.strconv][] could help you to safely translate strings stored
    externally to typed strings.

::: firebird.base.types.ZMQAddress

::: firebird.base.types.MIME

::: firebird.base.types.PyExpr

::: firebird.base.types.PyCode

::: firebird.base.types.PyCallable

Meta classes

::: firebird.base.types.SingletonMeta

::: firebird.base.types._SentinelMeta

::: firebird.base.types.CachedDistinctMeta

::: firebird.base.types.conjunctive

Functions

::: firebird.base.types.load