http://code.activestate.com/recipes/langs/python/tags/evaluation/2016-10-31T21:53:30-07:00ActiveState Code Recipes2016-10-31T21:53:30-07:00Vasudev Ramhttp://code.activestate.com/recipes/users/4173351/http://code.activestate.com/recipes/580712-easily-create-a-python-repl-in-python/

<p style="color: grey"> Python recipe 580712 by <a href="/recipes/users/4173351/">Vasudev Ram</a> (<a href="/recipes/tags/code_module/">code_module</a>, <a href="/recipes/tags/dynamic/">dynamic</a>, <a href="/recipes/tags/evaluation/">evaluation</a>, <a href="/recipes/tags/read_eval_print_loop/">read_eval_print_loop</a>, <a href="/recipes/tags/repl/">repl</a>). </p> <p>This recipe shows how to easily create a Python REPL (Read-Eval-Print Loop) in Python itself. This can allow the user to interact with a running Python program, including typing in Python statements at the REPL prompt, defining functions, using and changing variables that were set before the interaction started, and those variables modified during the interaction, will persist in the memory of the program, for any use, even after the interaction is over, as long as the program continues to run.</p>

2015-09-30T15:12:17-07:00Vasudev Ramhttp://code.activestate.com/recipes/users/4173351/http://code.activestate.com/recipes/579105-how-a-python-function-can-find-the-name-of-its-cal/

<p style="color: grey"> Python recipe 579105 by <a href="/recipes/users/4173351/">Vasudev Ram</a> (<a href="/recipes/tags/evaluation/">evaluation</a>, <a href="/recipes/tags/introspection/">introspection</a>, <a href="/recipes/tags/python/">python</a>, <a href="/recipes/tags/sys/">sys</a>). </p> <p>This recipe shows how a Python function can find out the name of its caller, i.e. which other Python function has called it.</p>

2011-02-24T10:17:32-08:00Jakub Jankiewiczhttp://code.activestate.com/recipes/users/4028109/http://code.activestate.com/recipes/577585-universal-eval-to-string-function/

<p style="color: grey"> Python recipe 577585 by <a href="/recipes/users/4028109/">Jakub Jankiewicz</a> (<a href="/recipes/tags/evaluation/">evaluation</a>, <a href="/recipes/tags/exec/">exec</a>, <a href="/recipes/tags/python/">python</a>, <a href="/recipes/tags/python_scripts/">python_scripts</a>). </p> <p>This is a function that evaluate all expressions and statements and return the result as a string. It also return Exceptions as strings. It is used in <a href="http://trypython.jcubic.pl">trypython.jcubic.pl</a></p>

2009-06-02T23:57:44-07:00Stephen Chappellhttp://code.activestate.com/recipes/users/2608421/http://code.activestate.com/recipes/576790-expression-evaluator/

<p style="color: grey"> Python recipe 576790 by <a href="/recipes/users/2608421/">Stephen Chappell</a> (<a href="/recipes/tags/evaluation/">evaluation</a>, <a href="/recipes/tags/expressions/">expressions</a>, <a href="/recipes/tags/parsing/">parsing</a>). Revision 4. </p> <p>After reading a portion of the book "The C# Programming Language: Third Edition," I found a section in the introduction that introduced abstract classes and methods that involved an example that included the concept of expression trees. The code was easy to implement since it just had to be copied out of the book. After playing around with the program a little and extending it, I thought that it would be fun to write a program in C# that could (interactively) evaluate expressions and display the results. Not knowing C# quite as well as Python led to the following program written and tested in Python 3.0 (not sure about previous languages).</p> <p>The first section of the code includes port of the program from the aforementioned book along with extra code that allows for further features not originally included in the C# version. Those sections are clearly marked as being new code written by yours truly. The second area of the program has six functions that are profusely documented so as to explain how they go about parsing and processing expressions entered for evaluation. For those wishing to use the code, the "run" function should be all that you need. The final part of the module contains a test program that can be used to check the validity of the how well the program works.</p> <p>The parser is not very complicated and will except expressions that are both normal to Python and completely illegal in Python. The main features are its ability to (1) identify simple assignment and mathematical operations, (2) identify constant floating point numbers, and (3) identify variables that would otherwise have no other meaning to the program. A limited number of error messages are given when appropriate but may leave one guessing what the problem really is. Mathematical operations are evaluated from left to right without regards to precedence, and assignment statements are evaluated from right to left.</p>

2009-04-26T18:10:55-07:00Sridhar Ratnakumarhttp://code.activestate.com/recipes/users/4169511/http://code.activestate.com/recipes/576720-lazy-property/

<p style="color: grey"> Python recipe 576720 by <a href="/recipes/users/4169511/">Sridhar Ratnakumar</a> (<a href="/recipes/tags/evaluation/">evaluation</a>, <a href="/recipes/tags/lazy/">lazy</a>, <a href="/recipes/tags/lazy_evaluation/">lazy_evaluation</a>). Revision 6. </p> <p>Python does not have lazy evaluation syntax features built-in, but fortunately decorators can be used with new-style classes to emulate such a feature. There are cases where one wants <code>foo.property</code> to return the actual property whose calculation takes significant amount of time.</p> <p>This recipe adapts the existing <code>property</code> to provide a <code>lazypropery</code> decorator that does this.</p> <p>See the first comment below for an example usage.</p> <p>Also see: <a href="http://en.wikipedia.org/wiki/Lazy_initialization">lazy initialization</a></p>