Editing Eval (section)

=== Python ===
In [[Python (language)|Python]], the <code>eval</code> function in its simplest form evaluates a single expression.

<code>eval</code> example (interactive shell):
<syntaxhighlight lang="pycon">
>>> x = 1
>>> eval('x + 1')
2
>>> eval('x')
1
</syntaxhighlight>

The <code>eval</code> function takes two optional arguments, <code>global</code> and <code>locals</code>, which allow the programmer to set up a restricted environment for the evaluation of the expression.

The <code>exec</code> statement (or the <code>exec</code> function in Python 3.x) executes statements:

<code>exec</code> example (interactive shell):
<syntaxhighlight lang="pycon">
>>> x = 1
>>> y = 1
>>> exec "x += 1; y -= 1"
>>> x
2
>>> y
0
</syntaxhighlight>

The most general form for evaluating statements/expressions is using code objects. Those can be created by invoking the <code>compile()</code> function and by telling it what kind of input it has to compile: an "<code>exec</code>" statement, an "<code>eval</code>" statement or a "<code>single</code>" statement:

<code>compile</code> example (interactive shell):
<syntaxhighlight lang="pycon">
>>> x = 1
>>> y = 2
>>> eval (compile ("print 'x + y = ', x + y", "compile-sample.py", "single"))
x + y =  3
</syntaxhighlight>