Commit | Line | Data |
---|---|---|
920dae64 AT |
1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> |
2 | <html> | |
3 | <head> | |
4 | <link rel="STYLESHEET" href="ref.css" type='text/css' /> | |
5 | <link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" /> | |
6 | <link rel='start' href='../index.html' title='Python Documentation Index' /> | |
7 | <link rel="first" href="ref.html" title='Python Reference Manual' /> | |
8 | <link rel='contents' href='contents.html' title="Contents" /> | |
9 | <link rel='index' href='genindex.html' title='Index' /> | |
10 | <link rel='last' href='about.html' title='About this document...' /> | |
11 | <link rel='help' href='about.html' title='About this document...' /> | |
12 | <link rel="next" href="unary.html" /> | |
13 | <link rel="prev" href="primaries.html" /> | |
14 | <link rel="parent" href="expressions.html" /> | |
15 | <link rel="next" href="unary.html" /> | |
16 | <meta name='aesop' content='information' /> | |
17 | <title>5.4 The power operator</title> | |
18 | </head> | |
19 | <body> | |
20 | <DIV CLASS="navigation"> | |
21 | <div id='top-navigation-panel' xml:id='top-navigation-panel'> | |
22 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> | |
23 | <tr> | |
24 | <td class='online-navigation'><a rel="prev" title="5.3.4 Calls" | |
25 | href="calls.html"><img src='../icons/previous.png' | |
26 | border='0' height='32' alt='Previous Page' width='32' /></A></td> | |
27 | <td class='online-navigation'><a rel="parent" title="5. Expressions" | |
28 | href="expressions.html"><img src='../icons/up.png' | |
29 | border='0' height='32' alt='Up One Level' width='32' /></A></td> | |
30 | <td class='online-navigation'><a rel="next" title="5.5 Unary arithmetic operations" | |
31 | href="unary.html"><img src='../icons/next.png' | |
32 | border='0' height='32' alt='Next Page' width='32' /></A></td> | |
33 | <td align="center" width="100%">Python Reference Manual</td> | |
34 | <td class='online-navigation'><a rel="contents" title="Table of Contents" | |
35 | href="contents.html"><img src='../icons/contents.png' | |
36 | border='0' height='32' alt='Contents' width='32' /></A></td> | |
37 | <td class='online-navigation'><img src='../icons/blank.png' | |
38 | border='0' height='32' alt='' width='32' /></td> | |
39 | <td class='online-navigation'><a rel="index" title="Index" | |
40 | href="genindex.html"><img src='../icons/index.png' | |
41 | border='0' height='32' alt='Index' width='32' /></A></td> | |
42 | </tr></table> | |
43 | <div class='online-navigation'> | |
44 | <b class="navlabel">Previous:</b> | |
45 | <a class="sectref" rel="prev" href="calls.html">5.3.4 Calls</A> | |
46 | <b class="navlabel">Up:</b> | |
47 | <a class="sectref" rel="parent" href="expressions.html">5. Expressions</A> | |
48 | <b class="navlabel">Next:</b> | |
49 | <a class="sectref" rel="next" href="unary.html">5.5 Unary arithmetic operations</A> | |
50 | </div> | |
51 | <hr /></div> | |
52 | </DIV> | |
53 | <!--End of Navigation Panel--> | |
54 | ||
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 | ||
107 | <P> | |
108 | ||
109 | <DIV CLASS="navigation"> | |
110 | <div class='online-navigation'> | |
111 | <p></p><hr /> | |
112 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> | |
113 | <tr> | |
114 | <td class='online-navigation'><a rel="prev" title="5.3.4 Calls" | |
115 | href="calls.html"><img src='../icons/previous.png' | |
116 | border='0' height='32' alt='Previous Page' width='32' /></A></td> | |
117 | <td class='online-navigation'><a rel="parent" title="5. Expressions" | |
118 | href="expressions.html"><img src='../icons/up.png' | |
119 | border='0' height='32' alt='Up One Level' width='32' /></A></td> | |
120 | <td class='online-navigation'><a rel="next" title="5.5 Unary arithmetic operations" | |
121 | href="unary.html"><img src='../icons/next.png' | |
122 | border='0' height='32' alt='Next Page' width='32' /></A></td> | |
123 | <td align="center" width="100%">Python Reference Manual</td> | |
124 | <td class='online-navigation'><a rel="contents" title="Table of Contents" | |
125 | href="contents.html"><img src='../icons/contents.png' | |
126 | border='0' height='32' alt='Contents' width='32' /></A></td> | |
127 | <td class='online-navigation'><img src='../icons/blank.png' | |
128 | border='0' height='32' alt='' width='32' /></td> | |
129 | <td class='online-navigation'><a rel="index" title="Index" | |
130 | href="genindex.html"><img src='../icons/index.png' | |
131 | border='0' height='32' alt='Index' width='32' /></A></td> | |
132 | </tr></table> | |
133 | <div class='online-navigation'> | |
134 | <b class="navlabel">Previous:</b> | |
135 | <a class="sectref" rel="prev" href="calls.html">5.3.4 Calls</A> | |
136 | <b class="navlabel">Up:</b> | |
137 | <a class="sectref" rel="parent" href="expressions.html">5. Expressions</A> | |
138 | <b class="navlabel">Next:</b> | |
139 | <a class="sectref" rel="next" href="unary.html">5.5 Unary arithmetic operations</A> | |
140 | </div> | |
141 | </div> | |
142 | <hr /> | |
143 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
144 | </DIV> | |
145 | <!--End of Navigation Panel--> | |
146 | <ADDRESS> | |
147 | See <i><a href="about.html">About this document...</a></i> for information on suggesting changes. | |
148 | </ADDRESS> | |
149 | </BODY> | |
150 | </HTML> |