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Initial commit of OpenSPARC T2 design and verification files.
[OpenSPARC-T2-DV] / tools / src / nas,5.n2.os.2 / lib / python / html / python / whatsnew / node5.html
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53<H1><A NAME="SECTION000500000000000000000">
544 PEP 292: Simpler String Substitutions</A>
55</H1>
56
57<P>
58Some new classes in the standard library provide an alternative
59mechanism for substituting variables into strings; this style of
60substitution may be better for applications where untrained
61users need to edit templates.
62
63<P>
64The usual way of substituting variables by name is the <code>%</code>
65operator:
66
67<P>
68<div class="verbatim"><pre>
69&gt;&gt;&gt; '%(page)i: %(title)s' % {'page':2, 'title': 'The Best of Times'}
70'2: The Best of Times'
71</pre></div>
72
73<P>
74When writing the template string, it can be easy to forget the
75"<tt class="samp">i</tt>" or "<tt class="samp">s</tt>" after the closing parenthesis. This isn't a big
76problem if the template is in a Python module, because you run the
77code, get an ``Unsupported format character'' <tt class="exception">ValueError</tt>,
78and fix the problem. However, consider an application such as Mailman
79where template strings or translations are being edited by users who
80aren't aware of the Python language. The format string's syntax is
81complicated to explain to such users, and if they make a mistake, it's
82difficult to provide helpful feedback to them.
83
84<P>
85PEP 292 adds a <tt class="class">Template</tt> class to the <tt class="module">string</tt> module
86that uses "<tt class="samp">$</tt>" to indicate a substitution. <tt class="class">Template</tt> is a
87subclass of the built-in Unicode type, so the result is always a
88Unicode string:
89
90<P>
91<div class="verbatim"><pre>
92&gt;&gt;&gt; import string
93&gt;&gt;&gt; t = string.Template('$page: $title')
94&gt;&gt;&gt; t.substitute({'page':2, 'title': 'The Best of Times'})
95u'2: The Best of Times'
96</pre></div>
97
98<P>
99If a key is missing from the dictionary, the <tt class="method">substitute</tt> method
100will raise a <tt class="exception">KeyError</tt>. There's also a <tt class="method">safe_substitute</tt>
101method that ignores missing keys:
102
103<P>
104<div class="verbatim"><pre>
105&gt;&gt;&gt; t = string.SafeTemplate('$page: $title')
106&gt;&gt;&gt; t.safe_substitute({'page':3})
107u'3: $title'
108</pre></div>
109
110<P>
111<div class="seealso">
112 <p class="heading">See Also:</p>
113
114<dl compact="compact" class="seerfc">
115 <dt><a href="http://www.python.org/peps/pep-0292.html"
116 title="Simpler String Substitutions"
117 >PEP 292, <em>Simpler String Substitutions</em></a>
118 <dd>Written and implemented
119by Barry Warsaw.
120 </dl>
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Full OpenSPARC design & verification tarball including full HDL.