"To sort a dictionary" (Python)

2001-04-08T19:35:01-07:00

Python recipe 52306 by Alex Martelli (search). Revision 2.

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 keys (in a separate list). Sorting (key,value) pairs (items) is simplest, but not fastest.

Sorting dictionaries by value in Python 2.4 (Python)

2004-09-13T04:19:24-07:00

Python recipe 304440 by Nick Coghlan (search).

Python 2.4 adds a new builtin function sorted(), which can make obtaining the items of a dictionary sorted by key or value a single line operation.

Random selection of elements in a list, with no repeats (Python)

2002-06-05T05:50:10-07:00

Python recipe 59883 by Iuri Wickert (search). Revision 2.

The simplest, direct way of consuming a list in a random fashion is painfully slow for list with a few 100's of elements. There are equally simple, but much faster ways to do this.

Python Binary Search Tree (Python)

2011-01-10T02:27:08-08:00

Python recipe 577540 by Edward Loper (algorithms, maximum, minimum, search, sort). Revision 2.

A data structure that holds a sorted collection of values, and supports efficient insertion, deletion, sorted iteration, and min/max finding. Values may sorted either based on their natural ordering, or on a key function (specified as an argument to the search tree's constructor). The search tree may contain duplicate values (or multiple values with equal keys) -- the ordering of such values is undefined.

This implementation was made with efficiency in mind. In particular, it is more than twice as fast as the other native-Python implementations I tried (which all use objects to store search tree nodes).

Find Multiple Elements In a List (Python)

2011-11-05T23:40:41-07:00

Python recipe 577943 by Alexander James Wallar (enumerate, find, list, search, search_list).

This algorithm searches for more than one element in a list. The input is a list that you want to search through and a list of elements that you want to search for. The output is a multidimensional list with the positions of the elements you are searching for in the search list in the order that you listed them.

grep in Python (Python)

2014-03-05T19:47:50-08:00

Python recipe 578845 by Andy Dustman (generator, grep, search).

The grep() function is inspired by UNIX grep, but is not limited to string patterns and files or streams.

Reorder a sequence (uses generators, and recursion!) (Python)

2003-11-28T12:54:43-08:00

Python recipe 252178 by Michael Davies (search).

Small function to generate every permutation of a given sequence. Works for lists and strings

extract email addresses from files (Python)

2002-07-10T16:38:29-07:00

Python recipe 138889 by carl scharenberg (search).

A quick way to find valid email addresses in text files using a regular expression search. It then removes duplicate entries and returns the results in a list.

Select the nth smallest element (Python)

2004-03-05T08:51:37-08:00

Python recipe 269554 by Raymond Hettinger (search). Revision 6.

O(n) quicksort style algorithm for looking up data based on rank order. Useful for finding medians, percentiles, quartiles, and deciles. Equivalent to data[n] when the data is already sorted.

Knuth-Morris-Pratt string matching (Python)

2002-03-01T23:49:23-08:00

Python recipe 117214 by David Eppstein (search).

This is an implementation of the Knuth-Morris-Pratt algorithm for finding copies of a given pattern as a contiguous subsequence of a larger text. Since KMP accesses the text only sequentially, it is natural to implement it in a way that allows the text to be an arbitrary iterator. After a preprocessing stage which takes time linear in the length of the pattern, each text symbol is processed in constant amortized time.

Binary search and insert in Python (Python)

2001-04-25T05:09:37-07:00

Python recipe 54159 by Noah Spurrier (search). Revision 3.

This demonstrates a simple binary search through sorted data. A binary search is a basic algorithm provided by bisect in Python. The binary search can be summarized by two lines of code: list.sort() item_insert_point = bisect.bisect (list, item)

Just For Fun: Quicksort in 3 Lines (Python)

2001-08-07T20:58:18-07:00

Python recipe 66473 by Nathan Gray (search). Revision 4.

OK, 4 lines if you count wrapped lines. :^) This is a rather naive implementation of quicksort that illustrates the expressive power of list comprehensions. DO NOT USE THIS IN REAL CODE!

NOTE: Due to an annoyance in the ASPN submission filters you must manually remove the space after the '\' character in the third line if you intend to use the code. Otherwise you will get a syntax error.

Sort a string using numeric order (Python)

2002-06-25T08:17:18-07:00

Python recipe 135435 by Chui Tey (search).

This recipe sorts a list of strings using the numeric order where possible.

Fuzzy matching dictionary (Python)

2006-03-18T11:23:25-08:00

Python recipe 475148 by Mark Mc Mahon (search).

This is more an ease of use subclass of dict - rather then one that uses a lot of dict features.

If your requested item is in the dictionary (with a key that hashes the same) then it acts as a more or less normal dictionary.

If on the other hand you are looking for a string that is similar to a key in the dictionary, then the class iterates over all the keys and finds the one that is the closest match.

Priority dict: a priority queue with updatable priorities (Python)

2007-06-26T09:20:06-07:00

Python recipe 522995 by Matteo Dell'Amico (search).

You may have needed a priority queue with the ability to change the priorities of elements that were in the queue. This recipe solves this problem in an efficient way.

Tkinter search box (Python)

2017-04-08T12:27:36-07:00

Python recipe 580773 by Miguel Martínez López (entry, search, searchbox, tkinter). Revision 9.

Instead of using two colors for active background and normal background, I use only one color and opacity parameter.

I trigger the feeling of a button using different colors when the mouse is and isn't over. Many modern HTML search boxes uses the same approach.

Command function receives text of entry box when button is pressed.

guaranteed-stable sort with the decorate-sort-undecorate idiom (aka Schwartzian transform) (Python)

2001-06-04T18:47:59-07:00

Python recipe 52234 by Alex Martelli (search). Revision 2.

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").

Setting up a listbox filter in Tkinter(python 2.7) (Python)

2014-04-10T10:25:38-07:00

Python recipe 578860 by Wykleph (filter, listbox, python, search, searchbar, tkinter). Revision 3.

If you have a listbox and need to filter the contents of the listbox based on the contents of an entry field, this will help you! Shoutout to Nikola-K for the revision. It's much simpler now :D

Lazy sorting (Python)

2004-05-03T12:30:10-07:00

Python recipe 280501 by Matteo Dell'Amico (search). Revision 2.

This generator will sort only the requested part of a list. Useful for getting just the first few elements of a list and avoiding the overhead of sorting the whole thing.

Python Multidimensional List Searcher (Python)

2011-10-29T22:21:39-07:00

Python recipe 577929 by Alexander James Wallar (element, elements, find, finder, list, python, search).

This module/function lets you find a 2 dimensional list of indices for elements you are looking for in a super list. Example:

find([1,1,1,2,1,2,3,3],[1,2,3])

returns: [[0, 1, 2, 4], [3, 5], [6, 7]]

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