.. _module:

.. py:module:: bitmath


The ``bitmath`` Module
######################

.. contents::
   :depth: 3
   :local:

Functions
*********

This section describes utility functions included in the
:py:mod:`bitmath` module.

.. _bitmath_getsize:

bitmath.getsize()
=================

.. function:: getsize(path[, bestprefix=True[, system=NIST]])

   Return a bitmath instance representing the size of a file at any
   given path.

   :param string path: The path of a file to read the size of
   :param bool bestprefix: **Default:** ``True``, the returned
                           instance will be in the best human-readable
                           prefix unit. If set to ``False`` the result
                           is a ``bitmath.Byte`` instance.
   :param system: **Default:** :py:data:`bitmath.NIST`. The preferred
                  system of units for the returned instance.
   :type system: One of :py:data:`bitmath.NIST` or :py:data:`bitmath.SI`

   Internally :py:func:`bitmath.getsize` calls
   :py:func:`os.path.realpath` before calling
   :py:func:`os.path.getsize` on any paths.

   Here's an example of where we'll run :py:func:`bitmath.getsize` on
   the bitmath source code using the defaults for the ``bestprefix``
   and ``system`` parameters:

   .. code-block:: python

      >>> import bitmath
      >>> print bitmath.getsize('./bitmath/__init__.py')
      33.3583984375 KiB

   Let's say we want to see the results in bytes. We can do this by
   setting ``bestprefix`` to ``False``:

   .. code-block:: python

      >>> import bitmath
      >>> print bitmath.getsize('./bitmath/__init__.py', bestprefix=False)
      34159.0 Byte

   Recall, the default for representation is with the best
   human-readable prefix. We can control the prefix system used by
   setting ``system`` to either :py:data:`bitmath.NIST` (the default)
   or :py:data:`bitmath.SI`:

   .. code-block:: python
      :linenos:
      :emphasize-lines: 1-4

      >>> print bitmath.getsize('./bitmath/__init__.py')
      33.3583984375 KiB
      >>> print bitmath.getsize('./bitmath/__init__.py', system=bitmath.NIST)
      33.3583984375 KiB
      >>> print bitmath.getsize('./bitmath/__init__.py', system=bitmath.SI)
      34.159 kB

   We can see in lines **1** → **4** that the same result is returned
   when ``system`` is not set and when ``system`` is set to
   :py:data:`bitmath.NIST` (the default).

   .. versionadded:: 1.0.7

bitmath.listdir()
=================

.. function:: listdir(search_base[, followlinks=False[, filter='*'[, relpath=False[, bestprefix=False[, system=NIST]]]]])

   This is a `generator
   <https://docs.python.org/2/tutorial/classes.html#generators>`_
   which recurses a directory tree yielding 2-tuples of:

   * The absolute/relative path to a discovered file
   * A bitmath instance representing the *apparent size* of the file

   :param string search_base: The directory to begin walking down
   :param bool followlinks: **Default:** ``False``, do not follow
                            links. Whether or not to follow symbolic
                            links to directories. Setting to ``True``
                            enables directory link following
   :param string filter: **Default:** ``*`` (everything). A glob to
                         filter results with. See `fnmatch
                         <https://docs.python.org/2/library/fnmatch.html>`_
                         for more details about *globs*
   :param bool relpath: **Default:** ``False``, returns the fully
                        qualified to each discovered file. ``True`` to
                        return the relative path from the present
                        working directory to the discovered file. If
                        ``relpath`` is ``False``, then
                        :py:func:`bitmath.listdir` internally calls
                        :py:func:`os.path.realpath` to normalize path
                        references
   :param bool bestprefix: **Default:** ``False``, returns
                           ``bitmath.Byte`` instances. Set to ``True``
                           to return the best human-readable prefix
                           unit for representation
   :param system: **Default:** :py:data:`bitmath.NIST`. Set a prefix
                  preferred unit system. Requires ``bestprefix`` is
                  ``True``
   :type system: One of :py:data:`bitmath.NIST` or :py:data:`bitmath.SI`

   .. note::

      * This function does **not** return tuples for directory
        entities. Including directories in results is `scheduled for
        introduction <https://github.com/tbielawa/bitmath/issues/27>`_
        in the upcoming 1.1.0 release.
      * Symlinks to **files** are followed automatically


   When interpreting the results from this function it is *crucial* to
   understand exactly which items are being taken into account, what
   decisions were made to select those items, and how their sizes are
   measured.

   Results from this function may seem invalid when directly compared
   to the results from common command line utilities, such as ``du``,
   or ``tree``.

   Let's pretend we have a directory structure like the following::

      some_files/
      ├── deeper_files/
      │   └── second_file
      └── first_file

   Where ``some_files/`` is a directory, and so is
   ``some_files/deeper_files/``. There are two regular files in this
   tree:

   * ``somefiles/first_file`` - 1337 Bytes
   * ``some_files/deeper_files/second_file`` - 13370 Bytes

   The **total** size of the files in this tree is **1337 + 13370 =
   14707** bytes.

   Let's call :py:func:`bitmath.listdir` on the ``some_files/``
   directory and see what the results look like. First we'll use all
   the default parameters, then we'll set ``relpath`` to ``True``:

   .. code-block:: python
      :linenos:
      :emphasize-lines: 5-6,10-11

      >>> import bitmath
      >>> for f in bitmath.listdir('./some_files'):
      ...     print f
      ...
      ('/tmp/tmp.P5lqtyqwPh/some_files/first_file', Byte(1337.0))
      ('/tmp/tmp.P5lqtyqwPh/some_files/deeper_files/second_file', Byte(13370.0))
      >>> for f in bitmath.listdir('./some_files', relpath=True):
      ...     print f
      ...
      ('some_files/first_file', Byte(1337.0))
      ('some_files/deeper_files/second_file', Byte(13370.0))

   On lines **5** and **6** the results print the full path, whereas
   on lines **10** and **11** the path is relative to the present
   working directory.

   Let's play with the ``filter`` parameter now. Let's say we only
   want to include results for files whose name begins with "second":

   .. code-block:: python

      >>> for f in bitmath.listdir('./some_files', filter='second*'):
      ...     print f
      ...
      ('/tmp/tmp.P5lqtyqwPh/some_files/deeper_files/second_file', Byte(13370.0))


   If we wish to avoid having to write for-loops, we can collect the
   results into a list rather simply:

   .. code-block:: python

      >>> files = list(bitmath.listdir('./some_files'))
      >>> print files
      [('/tmp/tmp.P5lqtyqwPh/some_files/first_file', Byte(1337.0)), ('/tmp/tmp.P5lqtyqwPh/some_files/deeper_files/second_file', Byte(13370.0))]

   Here's a more advanced example where we will sum the size of all
   the returned results and then play around with the possible
   formatting. Recall that a bitmath instance representing the size of
   the discovered file is the second item in each returned tuple.

   .. code-block:: python

      >>> discovered_files = [f[1] for f in bitmath.listdir('./some_files')]
      >>> print discovered_files
      [Byte(1337.0), Byte(13370.0)]
      >>> print reduce(lambda x,y: x+y, discovered_files)
      14707.0 Byte
      >>> print reduce(lambda x,y: x+y, discovered_files).best_prefix()
      14.3623046875 KiB
      >>> print reduce(lambda x,y: x+y, discovered_files).best_prefix().format("{value:.3f} {unit}")
      14.362 KiB


   .. versionadded:: 1.0.7



bitmath.parse_string()
======================

.. function:: parse_string(str_repr)

   .. versionadded:: 1.1.0

   Parse a string representing a unit into a proper bitmath
   object. All non-string inputs are rejected and will raise a
   :py:exc:`ValueError`. Strings without units are also rejected. See
   the examples below for additional clarity.

   :param string str_repr: The string to parse. May contain whitespace
                           between the value and the unit.
   :return: A bitmath object representing ``str_repr``
   :raises ValueError: if ``str_repr`` can not be parsed

   A simple usage example:

   .. code-block:: python

      >>> import bitmath
      >>> a_dvd = bitmath.parse_string("4.7 GiB")
      >>> print type(a_dvd)
      <class 'bitmath.GiB'>
      >>> print a_dvd
      4.7 GiB

   .. caution::

      Caution is advised if you are reading values from an unverified
      external source, such as output from a shell command or a
      generated file. Many applications (even ``/usr/bin/ls``) still
      do not produce file size strings with valid (or even correct)
      prefix units unless `specially configured to do so
      <https://www.gnu.org/software/coreutils/manual/html_node/Block-size.html#Block-size>`_. See
      :py:func:`bitmath.parse_string_unsafe` as an alternative.

   To protect your application from unexpected runtime errors it is
   recommended that calls to :py:func:`bitmath.parse_string` are
   wrapped in a ``try`` statement:

   .. code-block:: python

      >>> import bitmath
      >>> try:
      ...     a_dvd = bitmath.parse_string("4.7 G")
      ... except ValueError:
      ...    print "Error while parsing string into bitmath object"
      ...
      Error while parsing string into bitmath object


   Here we can see some more examples of invalid input, as well as two
   acceptable inputs:

   .. code-block:: python

      >>> import bitmath
      >>> sizes = [ 1337, 1337.7, "1337", "1337.7", "1337 B", "1337B" ]
      >>> for size in sizes:
      ...     try:
      ...         print "Parsed size into %s" % bitmath.parse_string(size).best_prefix()
      ...     except ValueError:
      ...         print "Could not parse input: %s" % size
      ...
      Could not parse input: 1337
      Could not parse input: 1337.7
      Could not parse input: 1337
      Could not parse input: 1337.7
      Parsed size into 1.3056640625 KiB
      Parsed size into 1.3056640625 KiB


   .. versionchanged:: 1.2.4
      Added support for parsing *octet* units via issue `#53 - parse
      french units
      <https://github.com/tbielawa/bitmath/issues/53>`_. The `usage
      <https://en.wikipedia.org/wiki/Octet_(computing)#Use>`_ of
      "octet" is still common in some `RFCs
      <https://en.wikipedia.org/wiki/Request_for_Comments>`_, as well
      as France, French Canada and Romania. See also, a table of the
      octet units and their values on `Wikipedia
      <https://en.wikipedia.org/wiki/Octet_(computing)#Unit_multiples>`_.

   Here are some simple examples of parsing *octet* based units:

   .. code-block:: python
      :linenos:
      :emphasize-lines: 4,5

      >>> import bitmath
      >>> a_mebibyte = bitmath.parse_string("1 MiB")
      >>> a_mebioctet = bitmath.parse_string("1 Mio")
      >>> print a_mebibyte, a_mebioctet
      1.0 MiB 1.0 MiB
      >>> print bitmath.parse_string("1Po")
      1.0 PB
      >>> print bitmath.parse_string("1337 Eio")
      1337.0 EiB

   Notice how on lines **4** and **5** that the variable
   ``a_mebibyte`` from the input ``1 MiB`` is exactly equivalent to
   ``a_mebioctet`` from the different input ``1 Mio``. This is because
   after :py:mod:`bitmath` parses the octet units the results are
   normalized into their **standard** NIST/SI equivalents
   automatically.


   .. note::

      If your input isn't compatible with
      :py:func:`bitmath.parse_string` you can try using
      :py:func:`bitmath.parse_string_unsafe`
      instead. :py:func:`bitmath.parse_string_unsafe` is more
      forgiving with input. Please read the documentation carefully so
      you understand the risks you assume using the ``unsafe`` parser.


bitmath.parse_string_unsafe()
=============================

.. function:: parse_string_unsafe(repr[, system=bitmath.SI])

   .. versionadded:: 1.3.1

   Parse a string or number into a proper bitmath object. This is the
   less strict version of the :py:func:`bitmath.parse_string`
   function. While :py:func:`bitmath.parse_string` only accepts SI and
   NIST defined unit prefixes, :py:func:`bitmath.parse_string_unsafe`
   accepts *non-standard* units such as those often displayed in
   command-line output. Examples following the description.

   :param repr: The value to parse. May contain whitespace between the
                value and the unit.

   :param system: :py:func:`bitmath.parse_string_unsafe` defaults to
                  parsing units as ``SI`` (base-10) units. Set the
                  ``system`` parameter to :py:data:`bitmath.NIST` if
                  you know your input is in ``NIST`` (base-2) format.

   :return: A bitmath object representing ``repr``
   :raises ValueError: if ``repr`` can not be parsed

   Use of this function comes with several caveats:

   * All inputs are assumed to be byte-based (as opposed to bit based)
   * Numerical inputs (those without any units) are assumed to be a number of bytes
   * Inputs with single letter units (``k``, ``M``, ``G``, etc) are
     assumed to be SI units (base-10). See the ``system`` parameter
     description **above** to change this behavior
   * Inputs with an ``i`` character following the leading letter (``Ki``,
     ``Mi``, ``Gi``) are assumed to be NIST units (base-2)
   * Capitalization does not matter

   What exactly are these *non-standard* units? Generally speaking
   non-standard units will not include enough information to be able
   to identify exactly which unit system is being used. This is caused
   by mis-capitalized characters (capital ``k``'s for SI *kilo* units
   when they should be lower case), or omitted Byte or Bit
   suffixes. You can find examples of non-standard units in many
   common command line functions or parameters. For example:

   * The ``ls`` command will print out single-letter units when given
     the ``-h`` option flag
   * Running ``qemu-img info virtualdisk.img`` will also report with
     single letter units
   * The ``df`` command also uses single-letter units
   * `Kubernetes
     <http://kubernetes.io/docs/user-guide/compute-resources/>`_ will
     display items like *memory limits* using two letter NIST units
     (ex: ``memory: 2370Mi``)

   Given those considerations, understanding exactly what values you
   are feeding into this function is crucial to getting accurate
   results. You can control the output of some commands with various
   option flags. For example, you could ensure the GNU ``ls`` and
   ``df`` commands print with SI values by providing the ``--si``
   option flag. By default those commands will print out using NIST
   (base-2) values.

   In this example let's pretend we're parsing the output of running
   ``df -H / /boot /home`` on our filesystems. Assume the output is
   saved into a file called ``/tmp/df-output.txt`` and looks like
   this::

      Filesystem                                 Size  Used Avail Use% Mounted on
      /dev/mapper/luks-ca8d5493-72bb-4691-afe1   107G   64G   38G  63% /
      /dev/sda1                                  500M  391M   78M  84% /boot
      /dev/mapper/vg_deepfryer-lv_home           129G  118G  4.7G  97% /home

   Now let's read this file, parse the ``Used`` column, and then print
   out the space used (line **7**):

   .. code-block:: python
      :linenos:
      :emphasize-lines: 7

      >>> with open('/tmp/df-output.txt', 'r') as fp:
      ...     # Skip parsing the 'df' header column
      ...     _ = fp.readline()
      ...     for line in fp.readlines():
      ...         cols = line.split()[0:4]
      ...         print """Filesystem: %s
      ... - Used: %s""" % (cols[0], bitmath.parse_string_unsafe(cols[1]))
      Filesystem: /dev/mapper/luks-ca8d5493-72bb-4691-afe1
      - Used: 107.0 GB
      Filesystem: /dev/sda1
      - Used: 500.0 MB
      Filesystem: /dev/mapper/vg_deepfryer-lv_home
      - Used: 129.0 GB


   If we had ran the ``df`` command with the ``-h`` option (instead of
   ``-H``) we will get base-2 (NIST) output. That would look like
   this::

     Filesystem                                 Size  Used Avail Use% Mounted on
     /dev/mapper/luks-ca8d5493-72bb-4691-afe1   100G   59G   36G  63% /
     /dev/sda1                                  477M  373M   75M  84% /boot
     /dev/mapper/vg_deepfryer-lv_home           120G  110G  4.4G  97% /home

   Because we switch from ``SI`` output to ``NIST`` output the values
   displayed are slightly different. **However** they still print
   using the same prefix unit, ``G``. We can tell
   :py:func:`bitmath.parse_string_unsafe` that the input is ``NIST``
   (base-2) by giving ``bitmath.NIST`` to the ``system`` parameter
   like this (line **8**):

   .. code-block:: python
      :linenos:
      :emphasize-lines: 8

      >>> with open('/tmp/df-output.txt', 'r') as fp:
      ...     # Skip parsing the 'df' header column
      ...     _ = fp.readline()
      ...     for line in fp.readlines():
      ...         cols = line.split()[0:4]
      ...         print """Filesystem: %s
      ... - Used: %s""" % (cols[0],
      ...                  bitmath.parse_string_unsafe(cols[1], \
      ...                      system=bitmath.NIST))
      Filesystem: /dev/mapper/luks-ca8d5493-72bb-4691-afe1
      - Used: 100.0 GiB
      Filesystem: /dev/sda1
      - Used: 477.0 MiB
      Filesystem: /dev/mapper/vg_deepfryer-lv_home
      - Used: 120.0 GiB

   The results printed use the proper NIST prefix unit syntax now:
   Capital **G** followed by a lower-case **i** ending with a capital
   **B**, ``GiB``.



bitmath.query_device_capacity()
===============================

.. function:: query_device_capacity(device_fd)

   Create :class:`bitmath.Byte` instances representing the capacity of
   a block device.

   :param file device_fd: An open file handle (``handle =
                          open('/dev/sda')``) of the target device.
   :return: A :class:`bitmath.Byte` equal to the size of ``device_fd``.
   :raises ValueError: if file descriptor ``device_fd`` is not of a
                       device type.
   :raises IOError:

      * :py:exc:`IOError[13]` - If the effective **uid** of this
        process does not have access to issue raw commands to block
        devices. I.e., this process does not have super-user rights.
      * :py:exc:`IOError[2]` - If the device ``device_fd`` points to
        does not exist.


   .. include:: query_device_capacity_warning.rst


   .. include:: example_block_devices.rst


   Here's an example using the ``with`` context manager to open a
   device and print its capacity with the best-human readable prefix
   (line **3**):

   .. code-block:: python
      :linenos:
      :emphasize-lines: 3

      >>> import bitmath
      >>> with open("/dev/sda") as device:
      ...     size = bitmath.query_device_capacity(device).best_prefix()
      ...     print "Device %s capacity: %s (%s Bytes)" % (device.name, size, size_bytes)
      Device /dev/sda capacity: 238.474937439 GiB (2.56060514304e+11 Bytes)


   .. important:: **Platform Notice**:
                  :py:func:`bitmath.query_device_capacity` is only
                  verified to work on **Linux** and **Mac OS X**
                  platforms. To file a bug report, please follow the
                  instructions in the :ref:`contributing
                  section<contributing_issue_reporting>`.

   .. versionadded:: 1.2.4

.. _module_context_managers:

Context Managers
****************

This section describes all of the `context managers
<https://docs.python.org/2/reference/datamodel.html#context-managers>`_
provided by the bitmath class.

.. warning::

   It is a known limitation that the bitmath context managers are
   **not thread-safe**. You may get unexpected results or errors using
   these in a threaded environment.

   The suggested workaround is to apply formatting to each object
   instance directly. See the instance :ref:`format
   <instances_format>` method docs for additional reference.


.. note::

   For a bit of background, a *context manager* (specifically, the
   ``with`` statement) is a feature of the Python language which is
   commonly used to:

   * Decorate, or *wrap*, an arbitrary block of code. I.e., effect a
     certain condition onto a specific body of code

   * Automatically *open* and *close* an object which is used in a
     specific context. I.e., handle set-up and tear-down of objects in
     the place they are used.

.. seealso::

   :pep:`343`
      *The "with" Statement*

   :pep:`318`
      *Decorators for Functions and Methods*


.. _module_bitmath_format:

bitmath.format()
================

.. function:: format([fmt_str=None[, plural=False[, bestprefix=False]]])

   The :py:func:`bitmath.format` context manager allows you to specify
   the string representation of all bitmath instances within a
   specific block of code.

   This is effectively equivalent to applying the
   :ref:`format()<instances_format>` method to an entire region of
   code.

   :param str fmt_str: a formatting mini-language compat formatting
                       string. See the :ref:`instance attributes
                       <instances_attributes>` for a list of available
                       items.
   :param bool plural: ``True`` enables printing instances with
                       trailing **s**'s if they're plural. ``False``
                       (default) prints them as singular (no trailing
                       's')
   :param bool bestprefix: ``True`` enables printing instances in
                           their best human-readable
                           representation. ``False``, the default,
                           prints instances using their current prefix
                           unit.


   .. note:: The ``bestprefix`` parameter is not yet implemented!

   Let's look at an example of toggling pluralization on and
   off. First we'll look over a demonstration script (below), and then
   we'll review the output.

   .. code-block:: python
      :linenos:
      :emphasize-lines: 33-34

      import bitmath

      a_single_bit = bitmath.Bit(1)
      technically_plural_bytes = bitmath.Byte(0)
      always_plural_kbs = bitmath.kb(42)

      formatting_args = {
          'not_plural': a_single_bit,
          'technically_plural': technically_plural_bytes,
          'always_plural': always_plural_kbs
      }

      print """None of the following will be pluralized, because that feature is turned off
      """

      test_string = """   One unit of 'Bit': {not_plural}

         0 of a unit is typically said pluralized in US English: {technically_plural}

         several items of a unit will always be pluralized in normal US English
         speech: {always_plural}"""

      print test_string.format(**formatting_args)

      print """
      ----------------------------------------------------------------------
      """

      print """Now, we'll use the bitmath.format() context manager
      to print the same test string, but with pluralization enabled.
      """

      with bitmath.format(plural=True):
          print test_string.format(**formatting_args)

   The context manager is demonstrated in lines **33** → **34**. In
   these lines we use the :py:func:`bitmath.format` context manager,
   setting ``plural`` to ``True``, to print the original string
   again. By doing this we have enabled pluralized string
   representations (where appropriate). Running this script would have
   the following output::


      None of the following will be pluralized, because that feature is turned off

         One unit of 'Bit': 1.0 Bit

         0 of a unit is typically said pluralized in US English: 0.0 Byte

         several items of a unit will always be pluralized in normal US English
         speech: 42.0 kb

      ----------------------------------------------------------------------

      Now, we'll use the bitmath.format() context manager
      to print the same test string, but with pluralization enabled.

         One unit of 'Bit': 1.0 Bit

         0 of a unit is typically said pluralized in US English: 0.0 Bytes

         several items of a unit will always be pluralized in normal US English
         speech: 42.0 kbs

   Here's a shorter example, where we'll:

   * Print a string containing bitmath instances using the default
     formatting (lines **2** → **3**)
   * Use the context manager to print the instances in scientific
     notation (lines **4** → **7**)
   * Print the string one last time to demonstrate how the formatting
     automatically returns to the default format (lines **8** → **9**)

   .. code-block:: python
      :linenos:

      >>> import bitmath
      >>> print "Some instances: %s, %s" % (bitmath.KiB(1 / 3.0), bitmath.Bit(512))
      Some instances: 0.333333333333 KiB, 512.0 Bit
      >>> with bitmath.format("{value:e}-{unit}"):
      ...     print "Some instances: %s, %s" % (bitmath.KiB(1 / 3.0), bitmath.Bit(512))
      ...
      Some instances: 3.333333e-01-KiB, 5.120000e+02-Bit
      >>> print "Some instances: %s, %s" % (bitmath.KiB(1 / 3.0), bitmath.Bit(512))
      Some instances: 0.333333333333 KiB, 512.0 Bit


   .. versionadded:: 1.0.8


.. _module_class_variables:

Module Variables
****************

This section describes the module-level variables. Some of which are
constants and are used for reference. Some of which effect output or
behavior.

.. versionchanged:: 1.0.7
   The formatting strings were not available for manupulate/inspection
   in earlier versions

.. versionadded:: 1.1.1
   Prior to this version :py:data:`ALL_UNIT_TYPES` was not defined

.. note:: Modifying these variables will change the default
          representation indefinitely. Use the
          :py:func:`bitmath.format` context manager to limit
          changes to a specific block of code.

.. _module_format_string:

.. py:data:: format_string

   This is the default string representation of all bitmath
   instances. The default value is ``{value} {unit}`` which, when
   evaluated, formats an instance as a floating point number with at
   least one digit of precision, followed by a character of
   whitespace, followed by the prefix unit of the instance.

   For example, given bitmath instances representing the following
   values: **1337 MiB**, **0.1234567 kb**, and **0 B**, their printed
   output would look like the following:

   .. code-block:: python

      >>> from bitmath import *
      >>> print MiB(1337), kb(0.1234567), Byte(0)
      1337.0 MiB 0.1234567 kb 0.0 Byte

   We can make these instances print however we want to. Let's wrap
   each one in square brackets (``[``, ``]``), replace the separating
   space character with a hyphen (``-``), and limit the precision to
   just 2 digits:

   .. code-block:: python

      >>> import bitmath
      >>> bitmath.format_string = "[{value:.2f}-{unit}]"
      >>> print bitmath.MiB(1337), bitmath.kb(0.1234567), bitmath.Byte(0)
      [1337.00-MiB] [0.12-kb] [0.00-Byte]

.. py:data:: format_plural

   A boolean which controls the pluralization of instances in string
   representation. The default is ``False``.

   If we wanted to enable pluralization we could set the
   :py:data:`format_plural` variable to ``True``. First, let's look at
   some output using the default singular formatting.

   .. code-block:: python

      >>> import bitmath
      >>> print bitmath.MiB(1337)
      1337.0 MiB

   And now we'll enable pluralization (line **2**):

   .. code-block:: python
      :linenos:
      :emphasize-lines: 2,5

      >>> import bitmath
      >>> bitmath.format_plural = True
      >>> print bitmath.MiB(1337)
      1337.0 MiBs
      >>> bitmath.format_plural = False
      >>> print bitmath.MiB(1337)
      1337.0 MiB

   On line **5** we disable pluralization again and then see that the
   output has no trailing "s" character.

.. py:data:: NIST

   Constant used as an argument to some functions to specify the
   **NIST** system.

.. py:data:: SI

   Constant used as an argument to some functions to specify the
   **SI** system.

.. py:data:: SI_PREFIXES

   An array of all of the SI unit prefixes (e.g., ``k``, ``M``, or
   ``E``)

.. py:data:: SI_STEPS

   .. code-block:: python

      SI_STEPS = {
          'Bit': 1 / 8.0,
          'Byte': 1,
          'k': 1000,
          'M': 1000000,
          'G': 1000000000,
          'T': 1000000000000,
          'P': 1000000000000000,
          'E': 1000000000000000000
      }


.. py:data:: NIST_PREFIXES

   An array of all of the NIST unit prefixes (e.g., ``Ki``, ``Mi``, or
   ``Ei``)


.. py:data:: NIST_STEPS

   .. code-block:: python

      NIST_STEPS = {
          'Bit': 1 / 8.0,
          'Byte': 1,
          'Ki': 1024,
          'Mi': 1048576,
          'Gi': 1073741824,
          'Ti': 1099511627776,
          'Pi': 1125899906842624,
          'Ei': 1152921504606846976
      }


.. py:data:: ALL_UNIT_TYPES

   An array of all combinations of known valid prefix units mixed with
   both bit and byte suffixes.

   .. code-block:: python

      ALL_UNIT_TYPES = ['b', 'B', 'kb', 'kB', 'Mb', 'MB', 'Gb', 'GB',
         'Tb', 'TB', 'Pb', 'PB', 'Eb', 'EB', 'Kib', 'KiB', 'Mib',
         'MiB', 'Gib', 'GiB', 'Tib', 'TiB', 'Pib', 'PiB', 'Eib',
         'EiB']

.. py:module:: bitmath.integrations

3rd Party Module Integrations
*****************************

This section describes the various ways in which :py:mod:`bitmath` can
be integrated with other 3rd pary modules.

To see a full demo of the :mod:`argparse` and :mod:`progressbar`
integrations, as well as a comprehensive demonstrations of the full
capabilities of the bitmath library, see :ref:`Creating Download
Progress Bars <real_life_examples_download_progress_bars>` in the
*Real Life Examples* section.

.. _bitmath_BitmathType:

argparse
========

.. versionadded:: 1.2.0

The `argparse module
<https://docs.python.org/2/library/argparse.html>`_ (part of stdlib)
is used to parse command line arguments. By default, parsed options
and arguments are turned into strings. However, one useful feature
:py:mod:`argparse` provides is the ability to `specify what datatype
<https://docs.python.org/2/library/argparse.html#type>`_ any given
argument or option should be interpreted as.

.. function:: BitmathType(bmstring)

   The :func:`BitmathType` factory creates objects that can be passed
   to the type argument of `ArgumentParser.add_argument()
   <https://docs.python.org/2/library/argparse.html#argparse.ArgumentParser.add_argument>`_. Arguments
   that have :func:`BitmathType` objects as their type will
   automatically parse the command line argument into a matching
   :ref:`bitmath object <classes>`.

   :param str bmstring: The command-line option to parse into a
                        bitmath object
   :returns: A bitmath object representing ``bmstring``
   :raises ValueError: on any input that
                       :py:func:`bitmath.parse_string` already rejects
   :raises ValueError: on **unquoted inputs** with whitespace
                       separating the value from the unit (e.g.,
                       ``--some-option 10 MiB`` is bad, but
                       ``--some-option '10 MiB'`` is good)

   Let's take a look at a more in-depth example.

   A feature found in many command-line utilities is the ability to
   specify some kind of file size using a string which roughly
   describes some kind of parameter. For example, let's look at the
   :program:`du` (disk usage) command. Invoking it as :option:`du -B`
   allows one to specify a desired block-size scaling factor in
   printed results.

   Let's say we wanted to implement a similar mechanism in an
   application of our own. Except, instead of abbreviating down to
   ambiguous capital letters, we accept scaling factors as
   :ref:`properly written values <appendix_on_units>` with associated
   units. Such as **10 MiB**, or **1 MB**.

   To accomplish this, we'll use :py:mod:`argparse` to create an
   argument parser and add one option to it, ``--block-size``. This
   option will have a type of :func:`BitmathType` set.

   .. code-block:: python
      :linenos:
      :emphasize-lines: 3,6,7

      >>> import argparse, bitmath
      >>> parser = argparse.ArgumentParser()
      >>> parser.add_argument('--block-size', type=bitmath.BitmathType)
      >>> args = "--block-size 1MiB"
      >>> results = parser.parse_args(args.split())
      >>> print type(results.block_size)
      <class 'bitmath.MiB'>

   On line **3** we add the ``--block-size`` option to the parser,
   explicitly defining it's type as :func:`BitmathType`. In lines
   **6** and **7** when we parse the provided arguments we find that
   :py:mod:`argparse` has automatically created a bitmath object for
   us.

   If an invalid scaling factor is provided by the user, such as one
   which does not represent a recognizable unit, the bitmath library
   will automatically detect this for us and signal to the argument
   parser that an error has occurred.


.. _bitmath_BitmathFileTransferSpeed:

progressbar
===========

.. versionadded:: 1.2.1

The `progressbar module
<https://github.com/niltonvolpato/python-progressbar>`_ is typically
used to display the progress of a long running task, such as a file
transfer operation. The module provides widgets for custom formatting
how exactly the 'progress' is displayed. Some examples include:
overall percentage complete, estimated time until completion, and an
ASCII progress bar which fills as the operation continues.

While :mod:`progressbar` already includes a widget suitable for
displaying `file transfer rates
<https://github.com/niltonvolpato/python-progressbar/blob/master/progressbar/widgets.py#L165>`_,
this widget does not support customizing its presentation, and is
limited to only prefix units from the SI system.


.. class:: BitmathFileTransferSpeed([system=bitmath.NIST, [format="{value:.2f} {unit}/s"]])

   The :class:`BitmathFileTransferSpeed` class is a more functional
   replacement for the upstream `FileTransferSpeed
   <https://github.com/niltonvolpato/python-progressbar/blob/master/progressbar/widgets.py>`_
   widget.

   While both widgets are able to calculate average transfer rates
   over a period of time, the :class:`BitmathFileTransferSpeed` widget
   adds new support for `NIST <appendix_on_units>`_ prefix units (the
   upstream widget only supports SI prefix units).

   In addition to NIST unit support, :class:`BitmathFileTransferSpeed`
   enables the user to have **full control** over the look and feel of
   the displayed rates.

   :param system: **Default:** :py:data:`bitmath.NIST`. The preferred
                  system of units for the printed rate.
   :type system: One of :py:data:`bitmath.NIST` or :py:data:`bitmath.SI`
   :param string format: a formatting mini-language compat formatting
                       string. **Default** ``{value:.2f} {unit}/s``
                       (e.g., ``13.37 GiB/s``)

   .. note::

      See :ref:`instance attributes <instances_attributes>` for a list
      of available formatting items. See the section on
      :ref:`formatting bitmath instances <instances_format>` for more
      information on this topic.


   Use :class:`BitmathFileTransferSpeed` exactly like the upstream
   ``FileTransferSpeed`` widget (example copied and modified from the
   progressbar project page):

   .. code-block:: python
      :linenos:
      :emphasize-lines: 2,4

      >>> from progressbar import ProgressBar, Percentage, Bar, ETA, RotatingMarker
      >>> from bitmath.integrations import BitmathFileTransferSpeed
      >>> widgets = ['Something: ', Percentage(), ' ', Bar(marker=RotatingMarker()),
      ...           ' ', ETA(), ' ', BitmathFileTransferSpeed()]
      >>> pbar = ProgressBar(widgets=widgets, maxval=10000000).start()
      >>> for i in range(1000000):
      ...     # do something
      ...     pbar.update(10*i+1)
      >>> pbar.finish()

   If this was ran from a script we would see output similar to the
   following::

      Something: 100% ||||||||||||||||||||||||||||||||||| Time: 0:00:01 9.27 MiB/s

   If we wanted behavior identical to :class:`FileTransferSpeed` we
   would set the ``system`` parameter to :py:data:`bitmath.SI` (line
   **5** below):

   .. code-block:: python
      :linenos:
      :emphasize-lines: 5

      >>> import bitmath
      >>> # ...
      >>> widgets = ['Something: ', Percentage(), ' ', Bar(marker=RotatingMarker()),
      ...           ' ', ETA(), ' ',
      ...           BitmathFileTransferSpeed(system=bitmath.SI)]
      >>> pbar = ProgressBar(widgets=widgets, maxval=10000000).start()
      >>> # ...

   If this was ran from a script we would see output similar to the
   following::

      Something: 100% ||||||||||||||||||||||||||||||||||| Time: 0:00:01 9.80 MB/s

   Note how the only difference is in the displayed unit. The former
   example produced a rate with a unit of ``MiB`` (a NIST unit)
   whereas the latter examples unit is ``MB`` (an SI unit).

   As noted previously, :class:`BitmathFileTransferSpeed` allows for
   full control over the formatting of the calculated rate of
   transfer.

   For example, if we wished to see the rate printed using more
   verbose language and plauralized units, we could do exactly that by
   constructing our widget in the following way:

   .. code-block:: python

      BitmathFileTransferSpeed(format="{value:.2f} {unit_plural} per second")

   And if this were run from a script like the previous examples::

      Something: 100% ||||||||||||||||||||||||||||||||||| Time: 0:00:01 9.41 MiBs per second
