This chapter describes modules (function and class libraries) which are built into MicroPython. There are a few categories of modules:

• Modules which implement a subset of standard Python functionality and are not intended to be extended by the user.
• Modules which implement a subset of Python functionality, with a provision for extension by the user (via Python code).
• Modules which implement MicroPython extensions to the Python standard libraries.
• Modules specific to a particular port and thus not portable.

Note about the availability of modules and their contents: This documentation in general aspires to describe all modules and functions/classes which are implemented in MicroPython. However, MicroPython is highly configurable, and each port to a particular board/embedded system makes available only a subset of MicroPython libraries. For officially supported ports, there is an effort to either filter out non-applicable items, or mark individual descriptions with "Availability:" clauses describing which ports provide a given feature. With that in mind, please still be warned that some functions/classes in a module (or even the entire module) described in this documentation may be unavailable in a particular build of MicroPython on a particular board. The best place to find general information of the availability/non-availability of a particular feature is the "General Information" section which contains information pertaining to a specific port.

Beyond the built-in libraries described in this documentation, many more modules from the Python standard library, as well as further MicroPython extensions to it, can be found in the micropython-lib repository.

The following standard Python libraries have been "micro-ified" to fit in with the philosophy of MicroPython. They provide the core functionality of that module and are intended to be a drop-in replacement for the standard Python library.

.. only:: not port_unix

    The modules are available by their u-name, and also by their non-u-name.  The
    non-u-name can be overridden by a file of that name in your package path.
    For example, ``import json`` will first search for a file ``json.py`` or
    directory ``json`` and load that package if it is found.  If nothing is found,
    it will fallback to loading the built-in ``ujson`` module.

.. only:: port_unix

    .. toctree::
       :maxdepth: 1

       array.rst
       builtins.rst
       cmath.rst
       gc.rst
       math.rst
       select.rst
       sys.rst
       ubinascii.rst
       ucollections.rst
       uhashlib.rst
       uheapq.rst
       uio.rst
       ujson.rst
       uos.rst
       ure.rst
       usocket.rst
       ustruct.rst
       utime.rst
       uzlib.rst

.. only:: port_pyboard

    .. toctree::
       :maxdepth: 1

       array.rst
       builtins.rst
       cmath.rst
       gc.rst
       math.rst
       select.rst
       sys.rst
       ubinascii.rst
       ucollections.rst
       uhashlib.rst
       uheapq.rst
       uio.rst
       ujson.rst
       uos.rst
       ure.rst
       usocket.rst
       ustruct.rst
       utime.rst
       uzlib.rst

.. only:: port_wipy

    .. toctree::
       :maxdepth: 1

       array.rst
       builtins.rst
       gc.rst
       select.rst
       sys.rst
       ubinascii.rst
       ujson.rst
       uos.rst
       ure.rst
       usocket.rst
       ussl.rst
       utime.rst

.. only:: port_esp8266

    .. toctree::
       :maxdepth: 1

       array.rst
       builtins.rst
       gc.rst
       math.rst
       sys.rst
       ubinascii.rst
       ucollections.rst
       uhashlib.rst
       uheapq.rst
       uio.rst
       ujson.rst
       uos.rst
       ure.rst
       usocket.rst
       ussl.rst
       ustruct.rst
       utime.rst
       uzlib.rst

Functionality specific to the MicroPython implementation is available in the following libraries.

.. toctree::
   :maxdepth: 1

   machine.rst
   micropython.rst
   network.rst
   uctypes.rst

.. only:: port_pyboard

   Libraries specific to the pyboard
   ---------------------------------

   The following libraries are specific to the pyboard.

   .. toctree::
      :maxdepth: 2

      pyb.rst

.. only:: port_wipy

   Libraries specific to the WiPy
   ---------------------------------

   The following libraries are specific to the WiPy.

   .. toctree::
      :maxdepth: 2

      wipy.rst

.. only:: port_esp8266

   Libraries specific to the ESP8266
   ---------------------------------

   The following libraries are specific to the ESP8266.

   .. toctree::
      :maxdepth: 2

      esp.rst