projects / OpenSPARC-T2-DV / blame
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| 55 | <H1><A NAME="SECTION007400000000000000000"></A><A NAME="power"></A> | |
| 56 | <BR> | |
| 57 | 5.4 The power operator | |
| 58 | </H1> | |
| 59 | ||
| 60 | <P> | |
| 61 | The power operator binds more tightly than unary operators on its | |
| 62 | left; it binds less tightly than unary operators on its right. The | |
| 63 | syntax is: | |
| 64 | ||
| 65 | <P> | |
| 66 | <dl><dd class="grammar"> | |
| 67 | <div class="productions"> | |
| 68 | <table> | |
| 69 | <tr> | |
| 70 | <td><a id='tok-power' xml:id='tok-power'>power</a></td> | |
| 71 | <td>::=</td> | |
| 72 | <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> | |
| 73 | </table> | |
| 74 | </div> | |
| 75 | <a class="grammar-footer" | |
| 76 | href="grammar.txt" type="text/plain" | |
| 77 | >Download entire grammar as text.</a> | |
| 78 | </dd></dl> | |
| 79 | ||
| 80 | <P> | |
| 81 | Thus, in an unparenthesized sequence of power and unary operators, the | |
| 82 | operators are evaluated from right to left (this does not constrain | |
| 83 | the evaluation order for the operands). | |
| 84 | ||
| 85 | <P> | |
| 86 | The power operator has the same semantics as the built-in | |
| 87 | <tt class="function">pow()</tt> function, when called with two arguments: it yields | |
| 88 | its left argument raised to the power of its right argument. The | |
| 89 | numeric arguments are first converted to a common type. The result | |
| 90 | type is that of the arguments after coercion. | |
| 91 | ||
| 92 | <P> | |
| 93 | With mixed operand types, the coercion rules for binary arithmetic | |
| 94 | operators apply. For int and long int operands, the result has the | |
| 95 | same type as the operands (after coercion) unless the second argument | |
| 96 | is negative; in that case, all arguments are converted to float and a | |
| 97 | float result is delivered. For example, <code>10**2</code> returns <code>100</code>, | |
| 98 | but <code>10**-2</code> returns <code>0.01</code>. (This last feature was added in | |
| 99 | Python 2.2. In Python 2.1 and before, if both arguments were of integer | |
| 100 | types and the second argument was negative, an exception was raised). | |
| 101 | ||
| 102 | <P> | |
| 103 | Raising <code>0.0</code> to a negative power results in a | |
| 104 | <tt class="exception">ZeroDivisionError</tt>. Raising a negative number to a | |
| 105 | fractional power results in a <tt class="exception">ValueError</tt>. | |
| 106 | ||
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| 143 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
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