Collection of Utilities
Project description
WorkToy v0.40.28
pip install worktoy
Table of Contents
WorkToyClass
Parent class providing general utility functions on the class itself.
from worktoy.worktoyclass import WorkToyClass
class MyClass(WorkToyClass):
"""Example class"""
def __init__(self, *args, **kwargs) -> None:
WorkToyClass.__init__(self, *args, **kwargs)
By inheriting from the WorkToyClass, instances now have access to a
collection of utility functions:
WorkToyClass.maybe
from typing import Any
from worktoy.worktoyclass import WorkToyClass
class MyClass(WorkToyClass):
"""Example class"""
def instanceMethod(self, *args) -> Any:
"""Instance method using ``maybe`` use a default argument value."""
return self.maybe(*args)
myInstance = MyClass()
myInstance.instanceMethod(None, [], ) # >>> []
WorkToyClass.maybeType
from worktoy.worktoyclass import WorkToyClass
class MyClass(WorkToyClass):
"""Example class"""
def instanceMethod(self, *args, **kwargs) -> int:
"""Instance method using ``maybeType`` to extract an integer from the
positional arguments. """
return self.maybeType(int, *args)
myInstance = MyClass()
myInstance.instanceMethod('one', 2, '3', 4, 5) # >>> 2
WorkToyClass.maybeTypes
from worktoy.worktoyclass import WorkToyClass
class MyClass(WorkToyClass):
"""Example class"""
def instanceMethod(self, *args, **kwargs) -> int:
"""Instance method using 'maybeTypes' to extract every integer from the
positional arguments."""
out = self.maybeTypes(int, *args)
if isinstance(out, int):
return out
myInstance = MyClass()
myInstance.instanceMethod('one', 2, '3', 4, 5) # >>> [2, 4, 5]
WorkToyClass.searchKey
from worktoy.worktoyclass import WorkToyClass
class MyClass(WorkToyClass):
"""Example class"""
def instanceMethod(self, *keys, **kwargs) -> int:
"""Instance method using ``searchKey`` to search for keyword argument
value."""
return self.searchKey(*keys, **kwargs)
myInstance = MyClass()
myInstance.instanceMethod('count', 'Count', 'amount', count=7) # >>> 7
WorkToyClass.searchKeys
from worktoy.worktoyclass import WorkToyClass
class MyClass(WorkToyClass):
"""Example class"""
def instanceMethod(self, *keys, **kwargs) -> int:
"""Instance method using ``searchKeys`` to search for every keyword
argument."""
return self.searchKeys(*keys, **kwargs)
myInstance = MyClass()
myInstance.instanceMethod('a', 'd', 'e', a=1, b=2, c=3, d=4) # >>> [1, 4]
WorkToyClass.maybeKey
from worktoy.worktoyclass import WorkToyClass
class MyClass(WorkToyClass):
"""Example class"""
def instanceMethod(self, *args, **kwargs) -> int:
"""Instance method using ``maybeKey`` to search for a keyword argument
value with a type restriction argument."""
return self.maybeKey(*args, **kwargs)
myInstance = MyClass()
myInstance.instanceMethod('a', 'b', int, a='1', b=2, c=3, d=4) # >>> 2
WorkToyClass.maybeKeys
from worktoy.worktoyclass import WorkToyClass
class MyClass(WorkToyClass):
"""Example class"""
def instanceMethod(self, *args, **kwargs) -> int:
"""Instance method using ``maybeKeys`` to search for every keyword
argument restricted to a certain type."""
return self.maybeKeys(*args, **kwargs)
myInstance = MyClass()
myInstance.instanceMethod('a', 'b', int, a=1, b=2, c=3, d=4) # >>> [1, 2]
WorkToyClass - Guards
The following methods are various type guards.
WorkToyClass.noneGuard
Raises UnavailableNameException if the given object is not None.
WorkToyClass.someGuard
Raises MissingArgumentException if given object is None
WorkToyClass.overRideGuard
Raises UnavailableNameException if given object is not None
WorkToyClass.functionGuard
Raises TypeSupportError if given object is not a function
WorkToyClass.intGuard
Raises TypeSupportError if given object is None or not an integer
WorkToyClass.floatGuard
Raises TypeSupportError if given object is None or not a float
WorkToyClass.strGuard
Raises TypeSupportError if given object is None or not a string
Descriptors
The Attribute class implements flexible descriptors.
class Attribute(WorkToyClass):
"""WorkToy - Fields - Field
Basic descriptor implementation."""
def __init__(self, defVal: Any = None, *args, **kwargs) -> None:
WorkToyClass.__init__(self, *args, **kwargs)
self._defaultValue = None
self._defaultType = None
case 1:
Receives a default value that is not a type
if defVal is not None and not isinstance(defVal, type):
self._setDefaultValue(defVal)
self._defaultType = type(self._defaultValue)
case 2:
Receives a default value that is a type. This is taken to mean that the attribute is to hold a value of that type. The type is then called without argument to attempt to create a default value.
if isinstance(defVal, type):
self._setDefaultValue(defVal)
self._defaultValue = defVal()
case 3
Receives no argument. In this case, the instance is
responsible for providing a default value. For example in the
instance __init__ method using the public setter.
Please note, that fields must do one of the following:
- Provide a default value in the Field creation call (RECOMMENDED)
- Define a Field type in the creation call. (NOT RECOMMENDED)
- Have the owning class defer default instance creation to the first call to the getter-function. This advanced use case allows the owning class to control specifically when and how to create instances. This is supported and encouraged, for advanced owning classes. (ADVANCED USE CASE)
- Subclass attribute to the specific type. (ADVANCED USE CASE)
ATTENTION!
Doing none of the above leads to HIGHLY UNDEFINED BEHAVIOUR! The Attribute is intended to raise MissingArgumentException in such cases.
self._fieldName = None
self._fieldOwner = None
self._getterFunctionName = None
self._setterFunctionName = None
self._deleterFunctionName = None
MetaClass
Metaclasses are certainly the most powerful tool available in Python
development. The WorkToy package provides a basic skeleton for
implementing custom metaclasses in the form of AbstractMetaClass and
AbstractNameSpace. Before explaining the merits of these, a
examination of how metaclasses work seem appropriate.
Introduction to metaclasses
You are already familiar with the default baseclass: type. In a
somewhat unfortunate choice of nomenclature, we face an ambiguity here:
do we mean type as in: isinstance(int, type) or do we mean:
type(int)? The first treats type as a type, but the second
treats type as a function. To illustrate how unfortunate this
nomenclature is, consider this expression:
type(type) is type or isinstance(type, type) >>> True
A metaclass is a custom type. Consider TestClass defined below:
from worktoy.worktoyclass import WorkToyClass
class TestClass(WorkToyClass):
"""Created with traditional class body."""
def __init__(self, *args, **kwargs) -> None:
WorkToyClass.__init__(self, *args, **kwargs)
def instanceMethod(self, *args, **kwargs) -> int:
"""Instance method"""
return self.maybeType(int, *args)
The above is entirely equivalent to:
from typing import Any
from worktoy.worktoyclass import WorkToyClass
def initFunc(instance: Any, *args, **kwargs) -> None:
"""Init function"""
WorkToyClass.__init__(instance, *args, **kwargs)
def someFunc(self, *args, **kwargs) -> int:
"""Instance Method"""
return self._maybeType(int, *args)
name = 'TestClass'
bases = (WorkToyClass,)
nameSpace = dict(__init__=initFunc, instanceMethod=someFunc)
TestClass = type(name, bases, nameSpace)
type
The type object used above specifies the creation of new classes. By
creating a custom metaclass, we are able to define our own class
creation. Below we define a metaclass that behaves entirely like
type allowing us to recognize the class creation we are familiar with
and see how we can change this behaviour.
(Please note, the naming convention: mcls: metaclass, cls: new
class, self new instance).
from typing import Any
class BaseMeta(type): # metaclasses inherit from type
"""Base metaclass behaving line ``type``"""
@classmethod
def __prepare__(mcls, name: str, bases: tuple[type], **kwargs) -> dict:
"""The prepare method creates the empty mapping object providing the
namespace for the newly created class. The base implementation
returns an empty instance of ``dict``."""
return {}
def __new__(mcls, name: str, bases: tuple[type], nameSpace: dict,
**kwargs) -> type:
"""The ``__new__`` method createds the new class,"""
cls = type.__new__(mcls, name, bases, nameSpace, **kwargs)
return cls
def __init__(cls, name: str, bases: tuple[type], nameSpace: dict,
**kwargs) -> None:
"""Once the new class is created it is initialised by this method. """
type.__init__(cls, name, bases, nameSpace, **kwargs)
def __call__(cls: type, *args, **kwargs) -> Any:
"""This method specifies how the newly creatd class creates instances
of itself. The default behaviour is as shown below: The instance is
created with the __new__ method on the newly created class, and then
it is initialized with the __init__ on the newly created class."""
self = cls.__new__(cls, )
cls.__init__(self, *args, **kwargs)
return self
By introducing custom metaclasses, we are free to customize the above steps to achieve any imaginable functionality. People say that Python does not support function overloading. What they mean is that function overloading in Python must be implemented at the metaclass level. (That is dumb, function overloading should not require custom metaclasses, but the point stands).
NameSpace
Customizing the __prepare__ method gives the greatest
opportunity to customize the class creation. Let us examine the
requirements for the namespace object returned by the __prepare__
method. When attempting to use a custom class for this purppose, one is
likely to encounter errors like:
"""TypeError: type.__new__() argument 3 must be dict, not NameSpace"""
"""TypeError: META.__prepare__() must return a mapping, not NameSpace"""
"""TypeError: ``NameSpace`` object does not support item assignment"""
It is possible to create a custom class that does not trigger any such
TypeError, which is able to create classes without any problem. Until
one day, you introduce a staticmethod and then receive:
"""
@staticmethod
^^^^^^^^^^^^
TypeError: ``NoneType`` object is not callable"""
What even is that error message? The above happens if the __getitem__
method on the namespace object does not raise a KeyError when receiving a
missing key. The expected behaviour from the namespace object receiving a
missing key is to raise a KeyError with the missing key as the message.
For example:
from typing import Any
def __getitem__(self, key: str, ) -> Any:
try:
dict.__getitem__(self, key)
except KeyError as e:
print(key)
raise e
By including the print statement, we can see that the problems occur where the class body has a valid expression without an equal sign. For example when decorating a function. Consider the following example:
from typing import Any, Callable
class NameSpace(dict, ):
"""NameSpace custom class"""
def __getitem__(self, key: str, ) -> Any:
"""Prints missing keys that are encountered."""
try:
return dict.__getitem__(self, key)
except KeyError as e:
print(key)
raise e
class META(type):
"""Metaclass implementing the __prepare__ method which returns an
instance of the NameSpace class."""
@classmethod
def __prepare__(mcls, name, bases, **kwargs) -> Any:
nameSpace = NameSpace()
return nameSpace
def func(f: Callable) -> None:
"""Decorator"""
return f
class TestClass(metaclass=META):
"""TestClass """
@staticmethod
@func
def a(self) -> None:
pass
if __name__ == '__main__':
TestClass()
When running the above script, we see the following printed to the console:
'__name__'
'staticmethod'
'func'
Fortunately, WorkToy provides the AbstractNameSpace class which
implements all required mapping functionality. Besides implementing
dict methods, it logs every line in the class body.
Wait A Minute!
In this module, WorkToy provides the custom exceptions used throughout the entire package.
MetaXcept
Just like the SYM module, the custom exceptions
implement a custom metaclass inheriting from AbstractMetaClass. This
metaclass MetaXcept uses a custom namespace class inheriting from the
AbstractNameSpace in its __prepare__ method.
Below is a reference list of the custom exceptions currently implemented:
MetaTypeSupportError
Description
Indicates that an instance is not a member of class derived from the correct metaclass.
Signature
from typing import Any
expMetaClass: type # The expected metaclass
actualValue: Any # The actual value received
argName: str # Argument name
FieldDecoderException
Custom exception raised when an instance of DataField attempts to decode
with default JSON decoder. The exception catches the JSONDecodeError and
brings additional information.
FieldEncoderException
Custom exception raised when an instance of DataField attempts to
serialize its value to JSON format, but where the value is not
serializable.
MissingArgumentException
Description
Invoked when a function is called before it is ready.
Signature
from typing import Any
missingArgument: str # Argument name
RecursiveCreateGetError
Description
Raised when a getter function calls a creator function a second time.
Signature
from worktoy.core import Function
from typing import Any
creator: Function # The expected type
variableType: type # The type of the variable
variableName: str # Argument name
TypeSupportError
Description
This exception should be raised when the argument type is not supported.
Signature
from typing import Any
expectedType: type # The expected type
actualValue: Any # The actual value received
argName: str # Argument name
UnavailableNameException
Description
Exception raised when a name is already occupied. Meaning that the named
argument were expected to be None.
Signature
from typing import Any
argName: str # The unavailable name
existingValue: Any # The present value at the name
newValue: str # The new value attempted to set
UnexpectedEventException
Description
Raised when receiving a QEvent of the wrong QEvent.Type. (Please note
that this exception is intended for use with the companion WorkSide
module.)
Signature
from typing import Any
expectedQEventType: str # The expected QEvent.Type
actualEvent: Any # The actual instance of QEvent received
argumentName: str # The argument name
UnsupportedSubclassException
Description
This exception should be raised when encountering a variable of correct type, but of incorrect subclass.
Signature
from typing import Any
argumentName: str # The argument name
expectedParent: type # The actual instance of QEvent received
actualValue: str # The actual value of the variable
Core
This module provides common types and constants.
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