OCRmyPDF/docs/api.rst

Using the OCRmyPDF API
======================

OCRmyPDF originated as a command line program and continues to have this legacy, but parts of it can be imported and used in other Python applications.

Some applications may want to consider running ocrmypdf from a subprocess call anyway, as this provides isolation of its activities.

Example
-------

OCRmyPDF one high-level function to run its main engine from an application. The parameters are symmetric to the command line arguments and largely have the same functions.

.. code-block:: python

    import ocrmypdf

    ocrmypdf.run('input.pdf', 'output.pdf', deskew=True)

With a few exceptions, all of the command line arguments are available and may be passed as equivalent keywords.

A few differences are that ``verbose`` and ``quiet`` are not available. Instead, output should be managed by configuring logging.

Parent process requirements
^^^^^^^^^^^^^^^^^^^^^^^^^^^

The :func:`ocrmypdf.ocrmypdf` function runs OCRmyPDF similar to command line execution. To do this, it will:
- create a monitoring thread
- create worker processes (forking itself)
- manage the signal flags of worker processes
0 execute other subprocesses (forking and executing other programs)

The Python process that calls ``ocrmypdf.run()`` must be sufficiently privileged to perform these actions. If it is not, ``ocrmypdf()`` will fail.

There is no currently no option to manage how jobs are scheduled other than the argument ``jobs=`` which will limit the number of worker processes.

Forking a child process to call ``ocrmypdf.run()`` is suggested. That way your application will survive even if OCRmyPDF does not.

Logging
^^^^^^^

OCRmyPDF will log under loggers named ``ocrmypdf``. In addition, it imports ``pdfminer`` and ``PIL``, both of which post log messages under those logging namespaces.

You can configure the logging as desired for your application or call :func:`ocrmypdf.configure_logging` to configure logging the same way OCRmyPDF itself does. The command line parameters such as ``--quiet`` and ``--verbose`` have no equivalents in the API; you must configure logging.

Progress monitoring
^^^^^^^^^^^^^^^^^^^

OCRmyPDF uses the ``tqdm`` package to implement its progress bars. :func:`ocrmypdf.configure_logging` will set up logging output to ``sys.stderr`` in a way that is compatible with the display of the progress bar.

Exceptions
^^^^^^^^^^

OCRmyPDF may throw standard Python exceptions, ``ocrmypdf.exceptions.*`` exceptions, some exceptions related to multiprocessing, and ``KeyboardInterrupt``. The parent process should provide an exception handler. OCRmyPDF will clean up its temporary files and worker processes automatically when an exception occurs.

Programs that call OCRmyPDF should consider trapping KeyboardInterrupt so that they allow OCR to terminate with the whole program terminating.

When OCRmyPDF succeeds conditionally, it may return an integer exit code.

Reference
---------

.. autofunction:: ocrmypdf.run

.. autoclass:: ocrmypdf.Verbosity
    :members:
    :undoc-members:

.. autoclass:: ocrmypdf.ExitCode
    :members:
    :undoc-members:

.. autofunction:: ocrmypdf.configure_logging