SciPy_SymPy/tutorial_sphinx/src/tutorial/printing.rst

.. _tutorial-printing:

==========
 Printing
==========

As we have already seen, SymPy can pretty print its output using Unicode
characters.  This is a short introduction to the most common printing options
available in SymPy.

Printers
========

There are several printers available in SymPy.  The most common ones are

- str
- repr
- ASCII pretty printer
- Unicode pretty printer
- LaTeX
- MathML
- Dot

In addition to these, there are also "printers" that can output SymPy objects
to code, such as C, Fortran, Javascript, Theano, and Python.  These are not
discussed in this tutorial.

Setting up Pretty Printing
==========================

If all you want is the best pretty printing, use the ``init_printing``
function.  This will automatically enable the best printer available in your
environment.

    >>> from sympy import init_printing
    >>> init_printing() # doctest: +SKIP

.. sidebar:: Quick Tip

   You an also change the printer used in SymPy Live.  Just change the "Output
   Format" in the settings.

If you plan to work in an interactive calculator-type session, the
``init_session`` function will automatically import everything in SymPy,
create some common Symbols, setup plotting, and run ``init_printing``.

    >>> from sympy import init_session
    >>> init_session() # doctest: +SKIP

    ::

       Python console for SymPy 0.7.2-git (Python 2.7.5-64-bit) (ground types: gmpy)

       These commands were executed:
       >>> from __future__ import division
       >>> from sympy import *
       >>> x, y, z, t = symbols('x y z t')
       >>> k, m, n = symbols('k m n', integer=True)
       >>> f, g, h = symbols('f g h', cls=Function)

       Documentation can be found at http://www.sympy.org

    >>>

In any case, this is what will happen:

- In the IPython QTConsole, if `\LaTeX` is installed, it will enable a printer
  that uses `\LaTeX`.

  .. image:: ../pics/ipythonqtconsole.png
     :height: 500

  If `\LaTeX` is not installed, but Matplotlib is installed, it will use the
  Matplotlib rendering engine. If Matplotlib is not installed, it uses the
  Unicode pretty printer.

- In the IPython notebook, it will use MathJax to render `\LaTeX`.

  .. image:: ../pics/ipythonnotebook.png
     :height: 250

- In an IPython console session, or a regular Python session, it will use the
  Unicode pretty printer if the terminal supports Unicode.

  .. image:: ../pics/consoleunicode.png
     :width: 700

- In a terminal that does not support Unicode, the ASCII pretty printer is
  used.

  .. image:: ../pics/consoleascii.png
     :width: 700

To explicitly not use `\LaTeX`, pass ``use_latex=False`` to ``init_printing``
or ``init_session``.  To explicitly not use Unicode, pass
``use_unicode=False``.


Printing Functions
==================

In addition to automatic printing, you can explicitly use any one of the
printers by calling the appropriate function.

str
---

To get a string form of an expression, use ``str(expr)``.  This is also the
form that is produced by ``print expr``.  String forms are designed to be easy
to read, but in a form that is correct Python syntax so that it can be copied
and pasted.  The ``str`` form of an expression will usually look exactly the
same as the expression as you would enter it.

    >>> from sympy import *
    >>> x, y, z = symbols('x y z')
    >>> str(Integral(sqrt(1/x), x))
    'Integral(sqrt(1/x), x)'
    >>> print Integral(sqrt(1/x), x)
    Integral(sqrt(1/x), x)

repr
----

The repr form of an expression is designed to show the exact form of an
expression.  It will be discussed more in the :ref:`tutorial-manipulation`
section.  To get it, use ``srepr`` [#srepr-fn]_.

    >>> srepr(Integral(sqrt(1/x), x))
    "Integral(Pow(Pow(Symbol('x'), Integer(-1)), Rational(1, 2)), Tuple(Symbol('x')))"

The repr form is mostly useful for understanding how an expression is built
internally.


ASCII Pretty Printer
--------------------

The ASCII pretty printer is accessed from ``pprint``.  If the terminal does
not support Unicode, the ASCII printer is used by default.  Otherwise, you
must pass ``use_unicode=False``.

    >>> pprint(Integral(sqrt(1/x), x), use_unicode=False)
      /
     |
     |     ___
     |    / 1
     |   /  -  dx
     | \/   x
     |
    /

``pprint`` prints the output to the screen.  If you want the string form, use
``pretty``.

    >>> pretty(Integral(sqrt(1/x), x), use_unicode=False)
    '  /          \n |           \n |     ___   \n |    / 1    \n |   /  -  dx\n | \\/   x    \n |           \n/            '
    >>> print pretty(Integral(sqrt(1/x), x), use_unicode=False)
      /
     |
     |     ___
     |    / 1
     |   /  -  dx
     | \/   x
     |
    /

Unicode Pretty Printer
----------------------

The Unicode pretty printer is also accessed from ``print``.  It the terminal
supports Unicode, it is used automatically.  It ``pprint`` is not able to
detect that the terminal supports unicode, you can pass ``use_unicode=True``.

    >>> pprint(Integral(sqrt(1/x), x), use_unicode=True)
    ⌠
    ⎮     ___
    ⎮    ╱ 1
    ⎮   ╱  ─  dx
    ⎮ ╲╱   x
    ⌡

`\LaTeX`
--------

To get the `\LaTeX` form of an expression, use ``latex``.

    >>> print latex(Integral(sqrt(1/x), x))
    \int \sqrt{\frac{1}{x}}\, dx

The ``latex`` function has many options to change the formatting of different
things.  See :py:meth:`its documentation <sympy.printing.latex.latex>` for
more details.

MathML
------

There is also a printer to MathML, called ``print_mathml``.  It must be imported
from ``sympy.printing.mathml``.

    >>> from sympy.printing.mathml import print_mathml
    >>> print_mathml(Integral(sqrt(1/x), x))
    <apply>
        <int/>
        <bvar>
            <ci>x</ci>
        </bvar>
        <apply>
            <root/>
            <apply>
                <power/>
                <ci>x</ci>
                <cn>-1</cn>
            </apply>
        </apply>
    </apply>

``print_mathml`` prints the output.  If you want the string, use the function
``mathml``.

Dot
---

The ``dotprint`` function in ``sympy.printing.dot`` prints output to dot
format, which can be rendered with Graphviz.  See the
:ref:`tutorial-manipulation` section for some examples of the output of this
printer.

.. rubric:: Footnotes

.. [#srepr-fn] SymPy does not use the Python builtin ``repr`` function for
   repr printing, because in Python ``str(list)`` calls ``repr`` on the
   elements of the list, and some SymPy functions return lists (such as
   ``solve``).  Since ``srepr`` is so verbose, it is unlikely that anyone
   would want it called by default on the output of ``solve``.