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.. "auto_examples/oop/call.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
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        Click :ref:`here <sphx_glr_download_auto_examples_oop_call.py>`
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.. rst-class:: sphx-glr-example-title

.. _sphx_glr_auto_examples_oop_call.py:


=============
3.14 __call__
=============
This lesson shows the usage of ``__call__`` method of a class.

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Suppose we have a function named `human`.

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.. code-block:: default



    def human(age):
        print(f"my age is {age}")
        return









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Since `human` is a function, we can **call** this function using ``()``.

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.. code-block:: default


    human(12)





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 .. code-block:: none

    my age is 12




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What if we want a class (or an instance of a class) to behave like function.
To be specific if we want to use an instance of a class as a function, so that
when we can call this instance, we will write ``__call__`` method of the class.

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.. code-block:: default



    class Human:

        def __init__(self, age):
            self.age = age

        def __call__(self):
            print(f"my age is {self.age}")
            return









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The `Human` class has two (user defined) methods i.e. ``__init__`` and ``__call__``.
The ``__init__`` method is used/called when we initialize th class and create its instance.

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.. code-block:: default


    human = Human(12)








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Now if we use the instance `human` as function i.e. if we call `human` using ``()``,
the ``__call__`` method will be executed.

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.. code-block:: default


    human()





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 .. code-block:: none

    my age is 12




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The ``__call__`` can be defined to take any keyword, non-keyword, optional or
obligatory arguments.

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.. code-block:: default



    class Human:

        def __init__(self, age):
            self.age = age

        def __call__(self, characteristic):
            print(f"I am {characteristic}")
            return


    human = Human(63)
    human("mortal")





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 .. code-block:: none

    I am mortal




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.. code-block:: default



    class Human:

        def __init__(self, age):
            self.age = age

        def __call__(self, *args, **kwargs):
            print(f"{args} {kwargs}")
            return


    human = Human(63)
    human()





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 .. code-block:: none

    () {}




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.. code-block:: default

    human(1)





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 .. code-block:: none

    (1,) {}




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.. code-block:: default

    human(1, a=2)





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 .. code-block:: none

    (1,) {'a': 2}




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Without writing, ``__call__`` method for the `Human` class, we wouldn't
be able to call the `Human` class or its instance `human`.

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**Question**:
In the code ``Human(1)()``, what does the second braces ``()``, those which
come after **(1)** represent?

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.. code-block:: default


    class Human:

        def __init__(self, age):
            self.age = age


    human = Human(2)

    # uncomment the following line
    # human()  # -> TypeError: 'Human' object is not callable.








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      .. image:: images/binder_badge_logo.svg
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      :download:`Download Python source code: call.py <call.py>`

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      :download:`Download Jupyter notebook: call.ipynb <call.ipynb>`


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