pak.dyn_value

Code for transforming certain values into dynamic values.

class DynamicValue(initial_value)

Bases: ABC

A definition of how to dynamically get one value from another.

Types and Packets have certain attributes whose values can be transformed into something callable-ish. DynamicValue is the mechanism behind that transformation.

To enroll a certain type into the DynamicValue machinery, make a subclass of DynamicValue, setting the _type attribute to the type in question. Doing so will “enable” the subclass on class initialization. This can be overridden by setting the _enabled attribute explicitly.

Alternatively, there are also the enable() and disable() methods, and the context() method for context management.

For instance, to enroll str into the machinery:

import pak

class StringDynamicValue(pak.DynamicValue):
    _type = str

    # The initial value is passed to
    # the constructor.
    def __init__(self, string):
        self.string = string

    # The dynamic value is returned
    # from the "get" method.
    #
    # Here we return the reversed string.
    def get(self, *, ctx=None):
        return self.string[::-1]

# This will lead to the following behavior:
v = pak.DynamicValue("Hello")
print(isinstance(v, StringDynamicValue))
print(v.get())

StringDynamicValue.disable()
print(pak.DynamicValue("Hello"))

True
olleH
Hello

Parameters:

initial_value – The initial value for the DynamicValue.

Returns:

If the type of inital_value is something for DynamicValue to deal with, then an instance of the appropriate subclass will be returned.

Otherwise, initial_value is returned.

Return type:

any

_type

The type for the DynamicValue to deal with.

Type:

type

_enabled

Whether the DynamicValue is enabled.

Type:

bool

classmethod enable()

Enables the class to be used in the DynamicValue machinery.

classmethod disable()

Disables the class to be used in the DynamicValue machinery.

classmethod context()

Temporarily enables then disables the class.

Examples

>>> import pak
>>> class StringToIntDynamicValue(pak.DynamicValue):
...     _type = str
...     def __init__(self, string):
...         self.string = string
...     def get(self, *, ctx=None):
...         return int(self.string)
...
>>> with StringToIntDynamicValue.context():
...     print(isinstance(pak.DynamicValue("1"), StringToIntDynamicValue))
...
True
>>> pak.DynamicValue("1")
'1'

abstract get(*, ctx=None)

Gets the dynamic value.

Parameters:

ctx (Packet.Context or Type.Context) – The context for the dynamic value.

Returns:

The dynamic value.

Return type:

any