tools/src/nas,5.n2.os.2/lib/python/html/python/ref/power.html

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<title>5.4 The power operator</title>
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<H1><A NAME="SECTION007400000000000000000"></A><A NAME="power"></A>
<BR>
5.4 The power operator
</H1>

<P>
The power operator binds more tightly than unary operators on its
left; it binds less tightly than unary operators on its right.  The
syntax is:

<P>
<dl><dd class="grammar">
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<tr>
    <td><a id='tok-power' xml:id='tok-power'>power</a></td>
    <td>::=</td>
    <td><a class='grammartoken' href="primaries.html#tok-primary">primary</a> ["**" <a class='grammartoken' href="unary.html#tok-u_expr">u_expr</a>]</td></tr>
</table>
</div>
<a class="grammar-footer"
  href="grammar.txt" type="text/plain"
  >Download entire grammar as text.</a>
</dd></dl>

<P>
Thus, in an unparenthesized sequence of power and unary operators, the
operators are evaluated from right to left (this does not constrain
the evaluation order for the operands).

<P>
The power operator has the same semantics as the built-in
<tt class="function">pow()</tt> function, when called with two arguments: it yields
its left argument raised to the power of its right argument.  The
numeric arguments are first converted to a common type.  The result
type is that of the arguments after coercion.

<P>
With mixed operand types, the coercion rules for binary arithmetic
operators apply. For int and long int operands, the result has the
same type as the operands (after coercion) unless the second argument
is negative; in that case, all arguments are converted to float and a
float result is delivered. For example, <code>10**2</code> returns <code>100</code>,
but <code>10**-2</code> returns <code>0.01</code>. (This last feature was added in
Python 2.2. In Python 2.1 and before, if both arguments were of integer
types and the second argument was negative, an exception was raised).

<P>
Raising <code>0.0</code> to a negative power results in a
<tt class="exception">ZeroDivisionError</tt>.  Raising a negative number to a
fractional power results in a <tt class="exception">ValueError</tt>.

<P>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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