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simpleeval (Simple Eval)
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A single file library for easily adding evaluatable expressions into
python projects. Say you want to allow a user to set an alarm volume,
which
could depend on the time of day, alarm level, how many previous alarms had
gone
off, and if there is music playing at the time.
Or if you want to allow simple formulae in a web application, but don't
want to
give full eval() access, or don't want to run in javascript on the client
side.
It's deliberately trying to stay simple to use and not have millions of
features,
pull it in from PyPI (pip or easy_install), or even just a single file you
can dump
into a project.
Internally, it's using the amazing python ast module to parse the
expression, which allows very fine control of what is and isn't allowed.
It
should be completely safe in terms of what operations can be performed by
the
expression.
The only issue I know to be aware of is that you can create an expression
which
takes a long time to evaluate, or which evaluating requires an awful lot of
memory, which leaves the potential for DOS attacks. There is basic
protection
against this, and you can lock it down further if you desire. (see the
Operators_ section below)
You should be aware of this when deploying in a public setting.
The defaults are pretty locked down and basic, and it's easy to add
whatever extra specific functionality you need (your own functions,
variable/name lookup, etc).
Basic Usage
-----------
To get very simple evaluating:
.. code-block:: python
from simpleeval import simple_eval
simple_eval("21 + 21")
returns 42.
Expressions can be as complex and convoluted as you want:
.. code-block:: python
simple_eval("21 + 19 / 7 + (8 % 3) ** 9")
returns ``535.714285714``.
You can add your own functions in as well.
.. code-block:: python
simple_eval("square(11)", functions={"square": lambda x: x*x})
returns 121.
For more details of working with functions, read further down.
Note:
~~~~~
all further examples use ``>>>`` to designate python code, as if you are
using
the python interactive prompt.
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