While developing Python software for Visual Effects pipelines, I found myself having to write the same boiler-plate code over and over again, as well as struggling with compatibility issues and feature gaps between Python 2.7 and Python 3.7+.

So I decided to implement solutions for those issues at the Base_, and basicco was born.

Base Classes

CompatBase ^^^^^^^^^^ The goal with the CompatBaseMeta metaclass and the CompatBase class is to bridge some of the feature gaps between Python 2.7 and Python 3.7+.

This includes adding Python 2.7 workarounds for:

Abstract properties <https://docs.python.org/3/library/abc.html#abc.abstractproperty>: Better abstractmethod decorator support for property-like descriptors. See also abstract_class.
PEP 487 <https://peps.python.org/pep-0487/>: Support for __init_subclass__ and __set_name__. See also init_subclass and set_name_.
object.__dir__ <https://docs.python.org/3/reference/datamodel.html#object.__dir__>: Base __dir__ method. See also default_dir.
__eq__ override <https://docs.python.org/3/reference/datamodel.html#object.__hash__>: Overriding __eq__ will set __hash__ to None. See also implicit_hash.
PEP 307 <https://peps.python.org/pep-0307/>: Support for pickling objects with __slots__. See also obj_state.
PEP 3155 <https://peps.python.org/pep-03155/>: Qualified name __qualname__ for nested classes. See also qualname.
__ne__ behavior <https://docs.python.org/3.0/whatsnew/3.0.html#operators-and-special-methods>: By default, __ne__ should negate the result of __eq__. See also safe_not_equals
PEP 0560 <https://peps.python.org/pep-0560/>: Better handling of Generic classes. See also tippo <https://github.com/brunonicko/tippo#generic-fixes>.

Base ^^^^ In addition to the compatibility solutions, the goal with the BaseMeta metaclass and the Base class is to add useful low-level features that hopefully yield better code readability and validation.

This includes:

__weakref__ slot: Added by default.
locked_class_: Public class attributes are read-only by default.
explicit_hash_: Overriding __eq__ without overriding __hash__ will error.
namespace_: Adds a protected __namespace unique to each class.
runtime_final_: Runtime checking for classes and methods decorated with final.

SlottedBase ^^^^^^^^^^^ The SlottedBase class and the SlottedBaseMeta metaclass offer all features from Base and BaseMeta plus implicit __slots__ declaration. See slotted <https://github.com/brunonicko/slotted>_ for more information.

Utilities

Apart from the features integrated into the base classes, basicco provides many general utility modules.

abstract_class ^^^^^^^^^^^^^^ Better support for abstract classes <https://docs.python.org/3/library/abc.html#abc.abstractmethod>_.

Provides abstract decorators that can be used directly on methods but also on property getters, classmethods, and staticmethods (even in Python 2.7).

.. code:: python

>>> from six import with_metaclass
>>> from basicco.abstract_class import AbstractMeta, abstract
>>> class Asset(with_metaclass(AbstractMeta, object)):
...     @abstract
...     def method(self):
...         pass
...
...     @property
...     @abstract
...     def prop(self):
...         return None
...
>>> Asset()
Traceback (most recent call last):
TypeError: Can't instantiate abstract class Asset...

caller_module ^^^^^^^^^^^^^ Retrieve the caller's module name.

.. code:: python

>>> from basicco.caller_module import caller_module
>>> def do_something():
...     return "I was called by {}".format(caller_module())
...
>>> do_something()
'I was called by __main__'

context_vars ^^^^^^^^^^^^ Backport of the contextvars module for Python 2.7, based on MagicStack/contextvars <https://github.com/MagicStack/contextvars>_.

When imported from Python 3, it simply redirects to the native contextvars <https://docs.python.org/3/library/contextvars.html>_ module.

.. code:: python

>>> from basicco.context_vars import ContextVar
>>> my_var = ContextVar("my_var", default="bar")
>>> token = my_var.set("foo")
>>> my_var.get()
'foo'
>>> my_var.reset(token)
>>> my_var.get()
'bar'

custom_repr ^^^^^^^^^^^ Custom representation functions for mappings, items, and iterables.

.. code:: python

>>> from basicco.custom_repr import mapping_repr
>>> dct = {"a": 1, "b": 2}
>>> mapping_repr(
...     dct,
...     prefix="<",
...     suffix=">",
...     template="{key}={value}",
...     sorting=True
... )
"<'a'=1, 'b'=2>"

.. code:: python

>>> from basicco.custom_repr import mapping_repr
>>> items = [("a", 1), ("b", 2)]
>>> mapping_repr(
...     items,
...     prefix="[", suffix="]",
...     template=(lambda i, key, value: key + " -> " + value),
... )
"['a' -> 1, 'b' -> 2]"

.. code:: python

>>> from basicco.custom_repr import iterable_repr
>>> tup = ("a", "b", "c", 1, 2, 3)
>>> iterable_repr(tup, prefix="<", suffix=">", value_repr=str)
'<a, b, c, 1, 2, 3>'

default_dir ^^^^^^^^^^^ Backport of Python 3's implementation of object.__dir__ <https://docs.python.org/3/reference/datamodel.html#object.__dir__>_.

This allows for calling super().__dir__() from a subclass to leverage the default implementation.

.. code:: python

>>> from six import with_metaclass
>>> from basicco.default_dir import DefaultDir
>>> class Class(DefaultDir):
...     def __dir__(self):
...         return super(Class, self).__dir__()
...
>>> obj = Class()
>>> dir(obj)
[...]

descriptors ^^^^^^^^^^^ Configurable descriptors.

.. code:: python

>>> from six import with_metaclass
>>> from basicco.descriptors import REMOVE, Descriptor, Owner
>>> class SlotDescriptor(Descriptor):
...     def __get_required_slots__(self):
...         return (self.name,)  # request a slot with the same name as this
...     def __get_replacement__(self):
...         return REMOVE  # remove this descriptor from the class body
...
>>> class PropDescriptor(Descriptor):
...     __slots__ = ("_slot_desc",)
...     def __init__(self, slot_desc):
...         super(PropDescriptor, self).__init__()
...         self._slot_desc = slot_desc
...     def __get__(self, instance, owner):
...         if instance is not None:
...             return getattr(instance, self._slot_desc.name)
...         return self
...     def __set__(self, instance, value):
...         setattr(instance, self._slot_desc.name, value)
...
>>> class Stuff(Owner):
...     _foo = SlotDescriptor()
...     _bar = SlotDescriptor()
...     foo = PropDescriptor(_foo)
...     bar = PropDescriptor(_bar)
...
>>> stuff = Stuff()
>>> stuff.foo = "foo"
>>> stuff.bar = "bar"
>>> stuff.foo
'foo'
>>> stuff.bar
'bar'

dynamic_class ^^^^^^^^^^^^^ Easily generate classes on the fly. This works best with a Base_ class. If provided a valid qualified name and module (uses caller_module_ by default), the class will be pickable/importable.

.. code:: python

>>> from basicco import Base
>>> from basicco.dynamic_class import make_cls
>>> class MyClass(object):
...     DynClass = make_cls("MyClass.DynClass", bases=(Base,), dct={"foo": "bar"})
...
>>> repr(MyClass.DynClass)
"<class '__main__.MyClass.DynClass'>"

dynamic_code ^^^^^^^^^^^^ Generate debuggable code on the fly that supports line numbers on tracebacks.

.. code:: python

>>> from basicco.dynamic_code import make_function, generate_unique_filename
>>> class MyClass(object):
...     pass
...
>>> bar = 'bar'
>>> # Prepare the script and necessary data.
>>> script = "\n".join(
...     (
...         "def __init__(self):",
...         "    self.foo = 'bar'",
...     )
... )
>>> # Gather information.
>>> name = "__init__"
>>> owner_name = MyClass.__name__
>>> module = MyClass.__module__
>>> filename = generate_unique_filename(name, module, owner_name)
>>> globs = {"bar": bar}
>>> # Make function and attach it as a method.
>>> MyClass.__init__ = make_function(name, script, globs, filename, module)
>>> obj = MyClass()
>>> obj.foo
'bar'

explicit_hash ^^^^^^^^^^^^^ Metaclass that forces __hash__ to be declared whenever __eq__ is declared.

.. code:: python

>>> from six import with_metaclass
>>> from basicco.explicit_hash import ExplicitHashMeta
>>> class Asset(with_metaclass(ExplicitHashMeta, object)):
...     def __eq__(self, other):
...         pass
...
Traceback (most recent call last):
TypeError: declared '__eq__' in 'Asset' but didn't declare '__hash__'

fabricate_value ^^^^^^^^^^^^^^^ Run a value through a callable factory (or None).

.. code:: python

>>> from basicco.fabricate_value import fabricate_value
>>> fabricate_value(None, 3)  # no factory, value passthrough
3
>>> fabricate_value(str, 3)  # callable factory
'3'
>>> fabricate_value("str", 3)  # use an import path
'3'
>>> fabricate_value(int)  # no input value, just the factory itself
0

func_tools ^^^^^^^^^^ Backport of functools.cache, functools.lru_cache, and functools.update_wrapper for Python 2.7.

.. code:: python

>>> from basicco.func_tools import cache
>>> @cache
... def calculate(a, b):
...     print("calculating...")
...     return a ** b
...
>>> calculate(2, 2)
calculating...
4
>>> calculate(2, 2)
4

get_mro ^^^^^^^ Get consistent MRO amongst different python versions. This works even with generic classes in Python 2.7.

.. code:: python

>>> from six import with_metaclass
>>> from tippo import Generic, TypeVar
>>> from basicco.get_mro import get_mro
>>> T = TypeVar("T")
>>> class MyGeneric(Generic[T]):
...     pass
...
>>> class SubClass(MyGeneric[T]):
...     pass
...
>>> class Mixed(SubClass[T], MyGeneric[T]):
...     pass
...
>>> [c.__name__ for c in get_mro(Mixed)]
['Mixed', 'SubClass', 'MyGeneric', 'Generic', 'object']

hash_cache_wrapper ^^^^^^^^^^^^^^^^^^ An integer subclass that pickles/copies as None. This can be used to avoid serializing a cached hash value.

.. code:: python

>>> from copy import copy
>>> from basicco.hash_cache_wrapper import HashCacheWrapper
>>> hash_cache = HashCacheWrapper(12345)
>>> print(hash_cache)
12345
>>> print(copy(hash_cache))
None

implicit_hash ^^^^^^^^^^^^^ Metaclass that forces __hash__ to None when __eq__ is declared. This is a backport of the default behavior in Python 3.

.. code:: python

>>> from six import with_metaclass
>>> from basicco.implicit_hash import ImplicitHashMeta
>>> class Asset(with_metaclass(ImplicitHashMeta, object)):
...     def __eq__(self, other):
...         pass
...
>>> Asset.__hash__ is None
True

import_path ^^^^^^^^^^^ Generate importable dot paths and import from them.

.. code:: python

>>> import itertools
>>> from basicco.import_path import get_path, import_path
>>> get_path(itertools.chain)
'itertools.chain'
>>> import_path("itertools.chain")
<... 'itertools.chain'>

.. code:: python

>>> from basicco.import_path import extract_generic_paths
>>> extract_generic_paths("Tuple[int, str]")
('Tuple', ('int', 'str'))

init_subclass ^^^^^^^^^^^^^ Backport of the functionality of __init_subclass__ from PEP 487 to Python 2.7. This works for both Python 2 (using __kwargs__) and 3 (using the new class parameters).

.. code:: python

>>> from basicco.init_subclass import InitSubclass
>>> class Foo(InitSubclass):
...     def __init_subclass__(cls, foo=None, **kwargs):
...         cls.foo = foo
...
>>> class Bar(Foo):
...     __kwargs__ = {"foo": "bar"}  # you can specify cls kwargs on py2 like this
...
>>> Bar.foo
'bar'

lazy_tuple ^^^^^^^^^^ Lazily-evaluated tuple-like structure.

.. code:: python

>>> from basicco.lazy_tuple import LazyTuple
>>> def expensive_generator():
...     for i in range(100):
...         yield i
...
>>> lazy_tuple = LazyTuple(expensive_generator())
>>> lazy_tuple[4]
4

locked_class ^^^^^^^^^^^^ Prevents changing public class attributes.

.. code:: python

>>> from six import with_metaclass
>>> from basicco.locked_class import LockedClassMeta
>>> class Foo(with_metaclass(LockedClassMeta, object)):
...     bar = "foo"
...
>>> Foo.bar = "bar"
Traceback (most recent call last):
AttributeError: can't set read-only class attribute 'bar'

mangling ^^^^^^^^ Functions to mangle/unmangle/extract private names.

.. code:: python

>>> from basicco.mangling import mangle, unmangle, extract
>>> mangle("__member", "Foo")
'_Foo__member'
>>> unmangle("_Foo__member", "Foo")
'__member'
>>> extract("_Foo__member")
('__member', 'Foo')

mapping_proxy ^^^^^^^^^^^^^ Mapping Proxy type (read-only dictionary) for older Python versions.

.. code:: python

>>> from basicco.mapping_proxy import MappingProxyType
>>> internal_dict = {"foo": "bar"}
>>> proxy_dict = MappingProxyType(internal_dict)
>>> proxy_dict["foo"]
'bar'

namespace ^^^^^^^^^ Wraps a dictionary/mapping and provides attribute-style access to it.

.. code:: python

>>> from basicco.namespace import Namespace
>>> ns = Namespace({"bar": "foo"})
>>> ns.bar
'foo'

.. code:: python

>>> from basicco.namespace import MutableNamespace
>>> ns = MutableNamespace({"bar": "foo"})
>>> ns.foo = "bar"
>>> ns.foo
'bar'
>>> ns.bar
'foo'

Also provides a NamespacedMeta metaclass that adds a __namespace protected class attribute that is unique to each class.

.. code:: python

>>> from six import with_metaclass
>>> from basicco.namespace import NamespacedMeta
>>> class Asset(with_metaclass(NamespacedMeta, object)):
...     @classmethod
...     def set_class_value(cls, value):
...         cls.__namespace.value = value
...
...     @classmethod
...     def get_class_value(cls):
...         return cls.__namespace.value
...
>>> Asset.set_class_value("foobar")
>>> Asset.get_class_value()
'foobar'

null_context ^^^^^^^^^^^^ Backport of contextlib.nullcontext for Python 2.7.

.. code:: python

>>> from basicco.null_context import null_context
>>> from basicco.suppress_exception import suppress_exception
>>> def myfunction(arg, ignore_exceptions=False):
...     if ignore_exceptions:
...         # Use suppress_exception to ignore all exceptions.
...         cm = suppress_exception(Exception)
...     else:
...         # Do not ignore any exceptions, cm has no effect.
...         cm = null_context()
...     with cm:
...         pass # Do something
...

obj_state ^^^^^^^^^ Get/update the state of an object, slotted or not (works even in Python 2.7).

.. code:: python

>>> from basicco.obj_state import get_state
>>> class Slotted(object):
...     __slots__ = ("foo", "bar")
...     def __init__(self, foo, bar):
...         self.foo = foo
...         self.bar = bar
...
>>> slotted = Slotted("a", "b")
>>> sorted(get_state(slotted).items())
[('bar', 'b'), ('foo', 'a')]

Also provides a ReducibleMeta metaclass that allows for pickling instances of slotted classes in Python 2.7.

qualname ^^^^^^^^ Python 2.7 compatible way of getting the qualified name. Based on wbolster/qualname <https://github.com/wbolster/qualname>_. Also provides a QualnamedMeta metaclass with a __qualname__ class property for Python 2.7.

recursive_repr ^^^^^^^^^^^^^^ Decorator that prevents infinite recursion for __repr__ methods.

.. code:: python

>>> from basicco.recursive_repr import recursive_repr
>>> class MyClass(object):
...
...     @recursive_repr
...     def __repr__(self):
...         return "MyClass<{!r}>".format(self)
...
>>> my_obj = MyClass()
>>> repr(my_obj)
'MyClass<...>'

runtime_final ^^^^^^^^^^^^^ Runtime-checked version of the typing.final <https://docs.python.org/3/library/typing.html#typing.final>_ decorator.

Can be used on methods, properties, classmethods, staticmethods, and classes that have RuntimeFinalMeta as a metaclass. It is also recognized by static type checkers and prevents subclassing and/or member overriding during runtime:

.. code:: python

>>> from six import with_metaclass
>>> from basicco.runtime_final import RuntimeFinalMeta, final
>>> @final
... class Asset(with_metaclass(RuntimeFinalMeta, object)):
...     pass
...
>>> class SubAsset(Asset):
...     pass
...
Traceback (most recent call last):
TypeError: can't subclass final class 'Asset'

.. code:: python

>>> from six import with_metaclass
>>> from basicco.runtime_final import RuntimeFinalMeta, final
>>> class Asset(with_metaclass(RuntimeFinalMeta, object)):
...     @final
...     def method(self):
...         pass
...
>>> class SubAsset(Asset):
...     def method(self):
...         pass
Traceback (most recent call last):
TypeError: 'SubAsset' overrides final member 'method' defined by 'Asset'

.. code:: python

>>> from six import with_metaclass
>>> from basicco.runtime_final import RuntimeFinalMeta, final
>>> class Asset(with_metaclass(RuntimeFinalMeta, object)):
...     @property
...     @final
...     def prop(self):
...         pass
...
>>> class SubAsset(Asset):
...     @property
...     def prop(self):
...         pass
Traceback (most recent call last):
TypeError: 'SubAsset' overrides final member 'prop' defined by 'Asset'

safe_not_equals ^^^^^^^^^^^^^^^ Backport of the default Python 3 behavior of __ne__ behavior for Python 2.7.

.. code:: python

>>> from six import with_metaclass
>>> from basicco.safe_not_equals import SafeNotEqualsMeta
>>> class Class(with_metaclass(SafeNotEqualsMeta, object)):
...     pass
...
>>> obj_a = Class()
>>> obj_b = Class()
>>> assert (obj_a == obj_a) is not (obj_a != obj_a)
>>> assert (obj_b == obj_b) is not (obj_b != obj_b)
>>> assert (obj_a == obj_b) is not (obj_a != obj_b)

safe_repr ^^^^^^^^^ Decorator that prevents __repr__ methods from raising exceptions and return a default representation instead.

.. code:: python

>>> from basicco.safe_repr import safe_repr
>>> class Class(object):
...     @safe_repr
...     def __repr__(self):
...         raise RuntimeError("oh oh")
...
>>> obj = Class()
>>> repr(obj)
"<__main__.Class object at ...; repr failed due to 'RuntimeError: oh oh'>"

sentinel ^^^^^^^^ Easily define singleton sentinel values and their type (for type hinting).

.. code:: python

>>> from basicco.sentinel import SentinelType
>>> class MissingType(SentinelType):
...     def __repr__(self):
...         return "MISSING"
...
>>> MISSING = MissingType()
>>> MISSING
MISSING
>>> MissingType() is MISSING
True
>>> isinstance(MISSING, MissingType)
True

set_name ^^^^^^^^ Backport of the functionality of __set_name__ from PEP 487 to Python 2.7.

.. code:: python

>>> from basicco.set_name import SetName
>>> class Attribute(object):
...     def __set_name__(self, owner, name):
...         self.owner = owner
...         self.name = name
...
>>> class Collection(SetName):
...     foo = Attribute()
...
>>> Collection.foo.owner is Collection
True
>>> Collection.foo.name
'foo'

suppress_exception ^^^^^^^^^^^^^^^^^^ Backport of contextlib.suppress for Python 2.7. See null_context_ for an example usage.

type_checking ^^^^^^^^^^^^^ Runtime type checking with support for import paths and type hints.

.. code:: python

>>> from tippo import Mapping, Literal
>>> from itertools import chain
>>> from basicco.type_checking import is_instance
>>> class SubChain(chain):
...     pass
...
>>> is_instance(3, int)
True
>>> is_instance(3, (chain, int))
True
>>> is_instance(3, ())
False
>>> is_instance(SubChain(), "itertools.chain")
True
>>> is_instance(chain(), "itertools.chain", subtypes=False)
True
>>> is_instance(SubChain(), "itertools.chain", subtypes=False)
False
>>> is_instance({"a": 1, "b": 2}, Mapping[str, int])
True
>>> is_instance("PRE", Literal["PRE", "POST"])
True

unique_iterator ^^^^^^^^^^^^^^^ Iterator that yields unique values.

.. code:: python

>>> from basicco.unique_iterator import unique_iterator
>>> list(unique_iterator([1, 2, 3, 3, 4, 4, 5]))
[1, 2, 3, 4, 5]

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