Callable

Callable#

A function in Python is a reusable block of code that performs a specific task. It can be executed with different sets of arguments, allowing for code abstraction and modularity by encapsulating operations into a single, callable unit.

Parameters#

A named entity in a function (or method) definition that specifies an argument (or in some cases, arguments) that the function can accept.

Find out more:

There are such types of parameters in python:

Name

Description

Syntax

Positional-only

Parameters that can be specified only positionally.

Parameters before the symbol /

Positional-or-keyword

Can be specified positionally as well as through keyword arguments.

Default parameters of the function

Var-positional

Parameter that takes values of all positional arguments that don’t correspond to the positional-only or positional-or-keyword parameters.

Parameter name begins with the * symbol; typical option is *args

Keyword-only

Can be specified only through keyword arguments.

Parameters that follow the Var-positional argument or just *

Var-keyword

Parameter that takes values of all keyword arguments that don’t correspond to the positional-or-keyword or keyword-only parameters.

Parameter name begins with **; typical option is **kwargs

You can define default values for parameters just by using syntax <parameter>=<default value>. But of you have defined default values for positional-only or for positional-or-keyword parameter all following parameters of these groups should have default values.

The following cell shows the definition of a function that contains all types of parameters, with default values defined for some of them, arranged in a way that forms a valid Python expression.

def some_function(
    positional_only1,
    positional_only2,
    /,
    positional1,
    positional2=None,
    *args,
    keyword_only1=None,
    keyword_only2,
    **kwargs 
):
    pass

User-defined functions#

The set of attributes specific for user-defined functions is represented in the following table:

Category

Attribute

Meaning

Read-only

function.__globals__

The dictionary that hold’s the function’s global variables

Writable

function.__doc__

The funciton’s documentation string, or None if unavailable

function.__name__

The funciton’s name

function.__qualname__

The funciton’s qualified name

function.__module__

The name of the module the function was defined in, or None

funciton.__defaults__

A tuple containing default parameter values, or None

For full list of attributes check: special read only attributes and special writable attributes.

The following cell defines the function and displays the values of some of the attributes specified user-defined attributes.

def hello_function(val = 10):
    pass

print(hello_function.__name__)
print(hello_function.__module__)
print(hello_function.__qualname__)

hello_function
__main__
hello_function

Note: The python documentation doesn’t specify it explicitly, but it appears that the instance methods are a kind of subset of the user-defined functions and generally have the same attributes.

The following cell defines the MyClass.fun method and displays the values of sertain attributes.

class MyClass:
    def fun(self):
        """Function's doc-string"""
        global hello

my_instance = MyClass()

print(my_instance.fun.__name__)
print(my_instance.fun.__doc__)

fun
Function's doc-string
{'__name__': '__main__', '__doc__': 'Automatically created module for IPython interactive environment', '__package__': None, '__loader__': None, '__spec__': None, '__builtin__': <module 'builtins' (built-in)>, '__builtins__': <module 'builtins' (built-in)>, '_ih': ['', 'def hello_function(val = 10):\n    pass\n\nhello_function.__name__', 'def hello_function(val = 10):\n    pass\n\nhello_function.dir', 'def hello_function(val = 10):\n    pass\n\nhello_function.dir()', 'def hello_function(val = 10):\n    pass\n\ndir(hello_function)', 'def hello_function(val = 10):\n    pass\n\nprint(hello_function.__name__)\nprint(hello_function.__module__)', 'def hello_function(val = 10):\n    pass\n\nprint(hello_function.__name__)\nprint(hello_function.__module__)\nprint(hello_function.__qualname__)', '---', 'class MyClass:\n    def fun(self):\n        pass\n\nmy_instance = MyClass()\nmy_instance.fun.__name__', 'class MyClass:\n    def fun(self, val: 10):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__defaults__)', 'class MyClass:\n    def fun(self, val: 10):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__defaults__)', 'class MyClass:\n    def fun(self, val: 10):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__defaults__)', 'class MyClass:\n    def fun(self):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__defaults__)', 'class MyClass:\n    def fun(self):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)', 'class MyClass:\n    def fun(self):\n        """Function"""\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)', 'class MyClass:\n    def fun(self):\n        """Function\'s doc-string"""\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)', 'class MyClass:\n    def fun(self):\n        """Function\'s doc-string"""\n        global hello\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)\nprint(my_instance.fun.__globals__)'], '_oh': {1: 'hello_function', 4: ['__annotations__', '__builtins__', '__call__', '__class__', '__closure__', '__code__', '__defaults__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__get__', '__getattribute__', '__getstate__', '__globals__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__kwdefaults__', '__le__', '__lt__', '__module__', '__name__', '__ne__', '__new__', '__qualname__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__type_params__'], 8: 'fun'}, '_dh': [PosixPath('/home/fedor/Documents/code/python/core/syntax')], 'In': ['', 'def hello_function(val = 10):\n    pass\n\nhello_function.__name__', 'def hello_function(val = 10):\n    pass\n\nhello_function.dir', 'def hello_function(val = 10):\n    pass\n\nhello_function.dir()', 'def hello_function(val = 10):\n    pass\n\ndir(hello_function)', 'def hello_function(val = 10):\n    pass\n\nprint(hello_function.__name__)\nprint(hello_function.__module__)', 'def hello_function(val = 10):\n    pass\n\nprint(hello_function.__name__)\nprint(hello_function.__module__)\nprint(hello_function.__qualname__)', '---', 'class MyClass:\n    def fun(self):\n        pass\n\nmy_instance = MyClass()\nmy_instance.fun.__name__', 'class MyClass:\n    def fun(self, val: 10):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__defaults__)', 'class MyClass:\n    def fun(self, val: 10):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__defaults__)', 'class MyClass:\n    def fun(self, val: 10):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__defaults__)', 'class MyClass:\n    def fun(self):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__defaults__)', 'class MyClass:\n    def fun(self):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)', 'class MyClass:\n    def fun(self):\n        """Function"""\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)', 'class MyClass:\n    def fun(self):\n        """Function\'s doc-string"""\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)', 'class MyClass:\n    def fun(self):\n        """Function\'s doc-string"""\n        global hello\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)\nprint(my_instance.fun.__globals__)'], 'Out': {1: 'hello_function', 4: ['__annotations__', '__builtins__', '__call__', '__class__', '__closure__', '__code__', '__defaults__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__get__', '__getattribute__', '__getstate__', '__globals__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__kwdefaults__', '__le__', '__lt__', '__module__', '__name__', '__ne__', '__new__', '__qualname__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__type_params__'], 8: 'fun'}, 'get_ipython': <bound method InteractiveShell.get_ipython of <ipykernel.zmqshell.ZMQInteractiveShell object at 0x7604cc1482f0>>, 'exit': <IPython.core.autocall.ZMQExitAutocall object at 0x7604cc14a900>, 'quit': <IPython.core.autocall.ZMQExitAutocall object at 0x7604cc14a900>, 'open': <function open at 0x7604d12523e0>, '_': 'fun', '__': ['__annotations__', '__builtins__', '__call__', '__class__', '__closure__', '__code__', '__defaults__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__get__', '__getattribute__', '__getstate__', '__globals__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__kwdefaults__', '__le__', '__lt__', '__module__', '__name__', '__ne__', '__new__', '__qualname__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__type_params__'], '___': 'hello_function', '__vsc_ipynb_file__': '/home/fedor/Documents/code/python/core/syntax/callable.ipynb', '_i': 'class MyClass:\n    def fun(self):\n        """Function\'s doc-string"""\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)', '_ii': 'class MyClass:\n    def fun(self):\n        """Function"""\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)', '_iii': 'class MyClass:\n    def fun(self):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)', '_i1': 'def hello_function(val = 10):\n    pass\n\nhello_function.__name__', 'hello_function': <function hello_function at 0x7604b489d6c0>, '_1': 'hello_function', '_i2': 'def hello_function(val = 10):\n    pass\n\nhello_function.dir', '_i3': 'def hello_function(val = 10):\n    pass\n\nhello_function.dir()', '_i4': 'def hello_function(val = 10):\n    pass\n\ndir(hello_function)', '_4': ['__annotations__', '__builtins__', '__call__', '__class__', '__closure__', '__code__', '__defaults__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__get__', '__getattribute__', '__getstate__', '__globals__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__kwdefaults__', '__le__', '__lt__', '__module__', '__name__', '__ne__', '__new__', '__qualname__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__type_params__'], '_i5': 'def hello_function(val = 10):\n    pass\n\nprint(hello_function.__name__)\nprint(hello_function.__module__)', '_i6': 'def hello_function(val = 10):\n    pass\n\nprint(hello_function.__name__)\nprint(hello_function.__module__)\nprint(hello_function.__qualname__)', '_i7': '---', '_i8': 'class MyClass:\n    def fun(self):\n        pass\n\nmy_instance = MyClass()\nmy_instance.fun.__name__', 'MyClass': <class '__main__.MyClass'>, 'my_instance': <__main__.MyClass object at 0x7604b48bc980>, '_8': 'fun', '_i9': 'class MyClass:\n    def fun(self, val: 10):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__defaults__)', '_i10': 'class MyClass:\n    def fun(self, val: 10):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__defaults__)', '_i11': 'class MyClass:\n    def fun(self, val: 10):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__defaults__)', '_i12': 'class MyClass:\n    def fun(self):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__defaults__)', '_i13': 'class MyClass:\n    def fun(self):\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)', '_i14': 'class MyClass:\n    def fun(self):\n        """Function"""\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)', '_i15': 'class MyClass:\n    def fun(self):\n        """Function\'s doc-string"""\n        pass\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)', '_i16': 'class MyClass:\n    def fun(self):\n        """Function\'s doc-string"""\n        global hello\n\nmy_instance = MyClass()\n\nprint(my_instance.fun.__name__)\nprint(my_instance.fun.__doc__)\nprint(my_instance.fun.__globals__)'}

Qualified name#

Qualified name is a dotted “path” of the global module’s namespace: For an object that defined in the current module.

Callable objects store their qualified names in the __qualname__ attribute.

The following cell defines nested classes structure:

class Outer():
    class Inner():
        def method(self):
            pass

The __qualname__ attribute values for different elements of the structure:

Outer.__qualname__

'Outer'

inner = Outer.Inner
inner.__qualname__

'Outer.Inner'

inner.method.__qualname__

'Outer.Inner.method'

Note: The __qualname__ for imported objects does not include the information about the module.

The following cell shows the __qualname__ of the unittest.TestCase.

from unittest import TestCase
TestCase.__qualname__

'TestCase'
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