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.. _compat:

Python Compatibility
====================

``calcpy`` is compatible with Python 3.8+ only since it depends on some features of Python 3.8.

It is not recommended to deploy it in older Python versions, but if you indeed want to support older Python versions, you can download source codes from GitHub and remove the dependencies in the source codes.

---------------------
Download Source Codes
---------------------

Visit http://www.github.com/zhiqingxiao/calcpy to download the source codes.

-------------------------------
Remove Dependency on Python 3.8
-------------------------------

The codes depend on Python 3.8 feature `positional only parameters (PEP 570) <https://peps.python.org/pep-0570/>`_.
In order to remove this dependency, you can remove all ``, /`` in the source codes.

The version ``__version__`` is generated by ``importlib.metadata``, which is available in Python 3.8.
In order to remove this dependency, you can replace ``importlib.metadata`` with the third-party package ``importlib_metadata``.

The file ``/_api.py`` uses some functions that are provided by Python 3.8+ only, including ``math.comb()``, ``math.dist()``, ``math.isqrt()``, ``math.prod()``. You can remove the the dependency by the following changes:

- Search ``comb = math.comb`` in ``/_api.py``. Remove it or change it the following codes:

.. code:: python

    def comb(n, k):
        """Calculate the number of ways to choose k items from n items without repetition and without order.

        Parameters:
            n: Number of items.
            k: Number of items to choose.

        Returns:
            The number of ways to choose k items from n items.

        Example:
            >>> comb(5, 2)
            10
            >>> comb(5, 0)
            1
        """
        if k < 0 or k > n:
            return 0
        if k == 0 or k == n:
            return 1
        k = min(k, n - k)
        c = 1
        for i in range(k):
            c = c * (n - i) // (i + 1)
        return c

- Search ``dist = math.dist`` in ``/_api.py``. Remove it or change it the following codes:

.. code:: python

    def dist(p, q):
        """Calculate the Euclidean distance between two points.

        Parameters:
            p: First point.
            q: Second point.

        Returns:
            The Euclidean distance between p and q.

        Examples:
            >>> dist([1, 2], [4, 6])
            5.0
            >>> dist((1, 2), (4, 6))
            5.0
        """
        return math.sqrt(sum((x - y) ** 2 for x, y in zip(p, q)))

- Search ``isqrt = math.isqrt`` in ``/_api.py``. Remove it or change it the following codes:

.. code:: python

    def isqrt(n):
        """Calculate the integer square root of a non-negative integer.

        Parameters:
            n: Non-negative integer.

        Returns:
            The integer square root of n.

        Example:
            >>> isqrt(16)
            4
            >>> isqrt(15)
            3
        """
        if n < 0:
            raise ValueError("Square root not defined for negative numbers")
        return int(n**0.5)

- Search ``prod = math.prod`` in ``/_api.py``. Remove it or change it the following codes:

.. code:: python

    def prod(iterable, start=1):
        """Calculate the product of all elements in an iterable.

        Parameters:
            iterable: An iterable object.
            start: Starting value.

        Returns:
            The product of all elements in the iterable.

        Example:
            >>> prod([1, 2, 3])
            6
            >>> prod([1, 2, 3], start=10)
            60
        """
        return functools.reduce(operator.mul, iterable, start)

-------------------------------
Remove Dependency on Python 3.7
-------------------------------

The ``__init__.py`` file uses the Python 3.7 feature `module __gettattr__ (PEP 562) <https://peps.python.org/pep-0562/>`_.
In order to remove the dependency, you can change the ``__getattr__`` function in ``__init__.py`` to the following codes:

.. code:: python

    class API:
        def __getattr__(self, name):
            return getcomponent(_api, name)

    api = API()

And then change relevant imports from ``calcpy`` to imports from ``calcpy.api``. For example, change ``from calcpy import add`` to ``from calcpy import api; add = api.add``.

The file ``/_api.py`` uses a function that are provided by Python 3.7+ only, i.e. ``math.remainder()``. You can remove the dependency by the following way:

- Search ``remainder = math.remainder`` in ``/_api.py``. Remove it or change it the following codes:

.. code:: python

    def remainder(x, y):
        """Calculate the remainder of x divided by y.

        Parameters:
            x: Dividend.
            y: Divisor.

        Returns:
            The remainder of x divided by y.

        Example:
            >>> remainder(5, 2)
            1.0
            >>> remainder(5, -2)
            -1.0
        """
        return x - y * math.floor(x / y)