http://code.activestate.com/recipes/users/97991/views/2001-08-31T15:17:32-07:00ActiveState Code Recipes2001-08-20T07:12:14-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/65207-constants-in-python/

<p style="color: grey"> Python recipe 65207 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/oop/">oop</a>). Revision 2. </p> <p>In Python, any variable can be re-bound at will -- and modules don't let you define special methods such as an instance's __setattr__ to stop attribute re-binding. Easy solution (in Python 2.1 and up): use an instance as "module"...</p>

2001-04-08T19:35:01-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/52306-to-sort-a-dictionary/

<p style="color: grey"> Python recipe 52306 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/search/">search</a>). Revision 2. </p> <p>Dictionaries can't be sorted -- a mapping has no ordering! -- so, when you feel the need to sort one, you no doubt want to sort its <em>keys</em> (in a separate list). Sorting (key,value) pairs (items) is simplest, but not fastest.</p>

2001-08-27T08:05:21-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/66531-singleton-we-dont-need-no-stinkin-singleton-the-bo/

<p style="color: grey"> Python recipe 66531 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/oop/">oop</a>). Revision 2. </p> <p>The Singleton design pattern (DP) has a catchy name, but the wrong focus -- on identity rather than on state. The Borg design pattern has all instances share state instead, and Python makes it, literally, a snap.</p>

2001-08-14T13:18:30-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/66516-add-an-entry-to-a-dictionary-unless-the-entry-is-a/

<p style="color: grey"> Python recipe 66516 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/shortcuts/">shortcuts</a>). Revision 2. </p> <p>Often, when working with a dictionary D, you need to use the entry D[k] if it's already present, or add a new D[k] if k wasn't a key into D. The setdefault method of dictionaries is a very handy shortcut for this task.</p>

2001-06-19T10:16:00-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/52304-static-methods-aka-class-methods-in-python/

<p style="color: grey"> Python recipe 52304 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/oop/">oop</a>). Revision 3. </p> <p>An attribute of a class-object is implicitly mutated into an unbound-method object if it starts out as a Python-coded function; thus, such functions must be wrapped as other callables if "just calling them" (without an instance-argument) is desired.</p>

2001-04-08T19:08:56-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/52308-the-simple-but-handy-collector-of-a-bunch-of-named/

<p style="color: grey"> Python recipe 52308 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/oop/">oop</a>). Revision 2. </p> <p>Often we want to just collect a bunch of stuff together, naming each item of the bunch; a dictionary's OK for that, but a small do-nothing class is even handier, and prettier to use.</p>

2001-08-31T15:17:32-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/52305-yet-another-python-templating-utility-yaptu/

<p style="color: grey"> Python recipe 52305 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/text/">text</a>). Revision 6. </p> <p>"Templating" (copying an input file to output, on the fly inserting Python expressions and statements) is a frequent need, and YAPTU is a small but complete Python module for that; expressions and statements are identified by arbitrary user-chosen regular-rexpressions.</p>

2001-07-17T03:24:20-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/66062-determining-current-function-name/

<p style="color: grey"> Python recipe 66062 by <a href="/recipes/users/97991/">Alex Martelli</a> . </p> <p>You want to determine the name of the currently running function, e.g. to create error messages that don't need to be changed when copied to other functions. Function _getframe of module sys does this and much more.</p>

2001-08-14T09:14:39-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/66517-ip-address-conversion-functions-with-the-builtin-s/

<p style="color: grey"> Python recipe 66517 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/network/">network</a>). </p> <p>Convert dotted-quad IP addresses to long integer and back, get network and host portions from an IP address, all nice and fast thanks to the builtin socket module (with a little help from the builtin struct module, too).</p>

2001-04-08T14:57:10-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/52310-conditionals-in-expressions/

<p style="color: grey"> Python recipe 52310 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/algorithms/">algorithms</a>). Revision 2. </p> <p>Python's "if" is a _statement_, and there is no conditional _operator_ (like C's "a?b:c" ternary) that we could use where expressions are needed (lambdas, etc); however, with some due care, equivalents can easily be coded.</p>

2001-06-18T05:28:27-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/65225-reversing-a-string-by-words-or-characters/

<p style="color: grey"> Python recipe 65225 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/text/">text</a>). </p> <p>You want to reverse the characters or words of a string.</p>

2001-08-15T16:47:48-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/66063-read-a-text-file-by-paragraph/

<p style="color: grey"> Python recipe 66063 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/files/">files</a>). Revision 2. </p> <p>Text files are most often read by-line, with excellent direct Python support. Sometimes we need to use other units, such as the paragraph -- a sequence of non-empty lines separated by empty lines. Python doesn't support that directly, but, as usual, it's not too hard to add such functionality.</p>

2001-07-16T08:14:17-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/66061-assign-and-test/

<p style="color: grey"> Python recipe 66061 by <a href="/recipes/users/97991/">Alex Martelli</a> . </p> <p>When transliterating C, Perl &amp;c to Python, one often misses idioms such as "if((x=foo())" or "while((x=foo())" -- but, it's easy to get them back, with one small utility class!</p>

2001-04-08T21:03:15-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/52295-automatic-delegation-as-an-alternative-to-inherita/

<p style="color: grey"> Python recipe 52295 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/oop/">oop</a>). Revision 2. </p> <p>Python classes cannot inherit from any type, just from other classes. However, automatic delegation (via __getattr__ and __setattr__) can provide pretty much the same functionality as inheritance (without such limits, and with finer-grained control).</p>

2001-03-26T12:02:44-08:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/52309-to-return-none-from-your-python-callable-c-functio/

<p style="color: grey"> Python recipe 52309 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/extending/">extending</a>). </p> <p>Often a function written in C for Python needs to return nothing in particular -- a "return None" in Python terms; but _don't_ just "return Py_None" from C, as that will mess up reference counts!</p>

2001-04-27T14:48:19-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/52236-various-idioms-for-call-my-superclasss-__init__-if/

<p style="color: grey"> Python recipe 52236 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/oop/">oop</a>). Revision 2. </p> <p>Python does not automatically call the __init__ (and __del__) methods of superclasses if subclasses define their own; explicit calling is needed, and it may be advisable to use a call-if-it-exists idiom.</p>

2001-06-04T18:47:59-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/52234-guaranteed-stable-sort-with-the-decorate-sort-unde/

<p style="color: grey"> Python recipe 52234 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/search/">search</a>). Revision 2. </p> <p>Python lists' .sort method is not guaranteed stable -- items that compare equal may or may not be in unchanged order. Ensuring stability is easy as one of the many application of the commom idiom decorate-sort-undecorate (aka "Schwartzian transform").</p>

2001-08-15T16:35:12-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/66509-a-simple-extension-type-for-python/

<p style="color: grey"> Python recipe 66509 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/extending/">extending</a>). Revision 2. </p> <p>C-coded Python extension types have an aura of mystery and difficulty they don't really deserve. Sure, it's a lot of work to implement every possible nicety, but a fundamental useful type doesn't take much.</p>

2001-06-18T05:01:58-07:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/65224-accessing-substrings/

<p style="color: grey"> Python recipe 65224 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/text/">text</a>). </p> <p>You want to access portions of a string. For example, you've read a fixed-width record and want to extract the fields.</p>

2001-03-12T08:06:55-08:00Alex Martellihttp://code.activestate.com/recipes/users/97991/http://code.activestate.com/recipes/52235-calling-a-superclasss-implementation-of-a-method/

<p style="color: grey"> Python recipe 52235 by <a href="/recipes/users/97991/">Alex Martelli</a> (<a href="/recipes/tags/oop/">oop</a>). </p> <p>Python has no equivalent to Java's "super" keyword (so that some part of a method can be delegated to the superclass), but it's easy to get similar convenience despite Python's multiple-inheritance generality.</p>