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.

Python add/set attributes to list (Python)

2015-09-29T16:28:46-07:00

Python recipe 579103 by webby1111 (attributes, class, dictionary, list, subclass). Revision 3.

Python Attribute List

Add/set attributes to python lists.

A google search for "add attributes to python lists" yields no good stackoverflow answer, hence the need for this.

Useful for machine learning stuff where you need labeled feature vectors.

This technique can be easily adapted for other built-ins (e.g. int).

The Problem

a = [1, 2, 4, 8]
a.x = "Hey!" # AttributeError: 'list' object has no attribute 'x'

The Solution

a = L(1, 2, 4, 8)
a.x = "Hey!"
print a       # [1, 2, 4, 8]
print a.x     # "Hey!"
print len(a)  # 4

# You can also do these:
a = L( 1, 2, 4, 8 , x="Hey!" )                 # [1, 2, 4, 8]
a = L( 1, 2, 4, 8 )( x="Hey!" )                # [1, 2, 4, 8]
a = L( [1, 2, 4, 8] , x="Hey!" )               # [1, 2, 4, 8]
a = L( {1, 2, 4, 8} , x="Hey!" )               # [1, 2, 4, 8]
a = L( [2 ** b for b in range(4)] , x="Hey!" ) # [1, 2, 4, 8]
a = L( (2 ** b for b in range(4)) , x="Hey!" ) # [1, 2, 4, 8]
a = L( 2 ** b for b in range(4) )( x="Hey!" )  # [1, 2, 4, 8]
a = L( 2 )                                     # [2]

Flattening an arbitrarily nested list in Python (Python)

2014-10-05T21:44:45-07:00

Python recipe 578948 by Vasudev Ram (algorithm, algorithms, flatten, list, lists, python).

This is a recipe to flatten a Python list which may have nested lists as items within it. It works for lists that have a maximum depth of nesting roughly equal to the recursion depth limit of Python, which is set to 1000 by default, though it can be increased with sys.setrecursionlimit().

Python 2.7 Linked List vs List (Python)

2010-08-13T04:05:42-07:00

Python recipe 577355 by Jack Trainor (educational, list).

Linked list implementation based on Python 2.7 collections.MutableSequence with a few benchmarks comparing the linked list with the built-in list type.

Random Binary List (Python)

2011-11-09T19:38:14-08:00

Python recipe 577944 by Alexander James Wallar (base, binary, list, math, numbers, python, random, random_binary_list).

This recipe returns a list of size n such that the contents of the returned list are random 0s and 1s. It returns a random binary list of size n.

Get multiple elements from a list (Python)

2011-11-21T06:41:57-08:00

Python recipe 577953 by Alexander James Wallar (get, getvar, list, python, retrieve, retrieving).

This code lets you retrieve multiple elements from a list at one time

List comparison, difference and more using set & frozenset (Python)

2012-11-01T10:30:58-07:00

Python recipe 578310 by Scott S-Allen (compare, contain, difference, lambda, list, remove, set, union).

Python has a powerful suite of tools for comparing lists by way of sets and frozensets. Here are a few examples and conveniences that many newcomers, even a few seasoned developers, are unaware.

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]]

Sorting a list of dictionary based on a key value (Python)

2008-08-20T03:30:37-07:00

Python recipe 576433 by riteshn (dictionary, list, sorting).

Here is a quick and dirty way to sort a list of dictionary based on a key value.

Get a list from a ConfigParser option (Python)

2011-05-13T13:53:56-07:00

Python recipe 577694 by Georges Martin (configparser, list, option). Revision 2.

Return a list from a ConfigParser option. By default, split on a comma and strip whitespaces.

Flattening an arbitrarily deep list (or any iterator) (Python)

2012-04-03T17:13:35-07:00

Python recipe 578092 by Garrett (flatten, iterator, itertools, list, python, tuple). Revision 6.

What if you had a list like this: [1, -10, [1,2,[3,4]], xrange(200)], and you just wanted to go through each element in order (wanted it to return a simple list of [1,-10,1,2,3,4,1,2,3,4...199])

I've seen a couple of attempts to flatten arbitrarily deep lists. Many of them involve recursion, like this one: http://rightfootin.blogspot.com/2006/09/more-on-python-flatten.html

Recursion is generally considered non-pythonic (at least to my knowledge), so I have used one which just involves simple iterators instead. Also, recursion will fail if the list is too deep (so it wouldn't really be arbitrary, would it?).

Flatten a list (or list of lists, etc.) (Python)

2011-03-01T03:46:26-08:00

Python recipe 577255 by Sunjay Varma (extend, flatten, list, optimization, python, smart). Revision 2.

I created this function sometime ago for my own purposes. It simply flattens a list.

Check out the first comment for another version of someone else's design.

Generate List of Numbers from Hyphenated and comma separeted string like "1-5,25-30,4,5" (Python)

2010-07-01T02:08:09-07:00

Python recipe 577279 by Siddhant Sanyam (hypen, list, range).

This function takes a range in form of "a-b" and generate a list of numbers between a and b inclusive. Also accepts comma separated ranges like "a-b,c-d,f" will build a list which will include numbers from a to b, a to d and f Example: hyphen_range('54-78') hyphen_range('57-78,454,45,1-10') hyphen_range('94-100,1052,2-50')

User List Subclass (Python)

2008-08-18T09:26:07-07:00

Python recipe 576428 by nosklo (list, slices, subclass, __getitem__). Revision 2.

As subclassing list has a problem when using __getitem__, __delitem__ and __setitem__ methods with slices (they don't get called because parent implements __getslice__, __delslice__ and __setslice__ respectively), I've coded this UserList class that is a subclass of list, but overwrites these methods. By subclassing this class, you can overwrite __getitem__ and it will be called correctly for slices.

Fast Indexing functions (greater than, less than, equal to, and not equal to) (Python)

2012-03-13T16:21:36-07:00

Python recipe 578071 by Garrett (index, list, list_comprehension, numpy, python). Revision 2.

Oftentimes you want to find the index of a list-like object. Numpy arrays, for example, do not have a index member function. These get the job done quickly.

Note: these do not raise exceptions, instead they return -1 on error. You should change that if you want different behavior.

List with fast membership test (contains) (Python)

2010-04-18T05:52:57-07:00

Python recipe 577185 by Paul Bohm (list, subclass). Revision 3.

Just a list subclass with a fast hash based __contains__ provided by a Set. Inheriting from list was far more work than I had anticipated AND the code below is still buggy.

Still, this provides O(1) indexed access and O(1) contains. If you use this expect the slicing code to be broken despite the attempts to get it right. Fixes graciously accepted!

Nest a flat list (Python)

2010-02-25T03:50:09-08:00

Python recipe 577061 by Sander Evers (list, nest, nested, unflatten). Revision 2.

Turn a flat list into a nested list, with a specified number of lists per nesting level.

Flatten a list (Python)

2010-06-18T03:45:20-07:00

Python recipe 577250 by Giannis Fysakis (flatten, list). Revision 3.

Flatten a list

Fixed Lengh List (Python)

2014-01-24T15:27:25-08:00

Python recipe 578813 by Hiro (length, list). Revision 2.

In some applications, it's advantageous to be able to define a fixed length list.

The class provides all features as python internal type: list

The main focus of fixed length list is only keep certain number of items. "overflow" items will be discarded.

Tkinter draggable list V2 (Python)

2017-03-03T14:13:14-08:00

Python recipe 580748 by Miguel Martínez López (draggable, list, tkinter). Revision 3.

This version use tkinter frame instead of ttk frame.

This next link is version 1 (It's the same code but it uses ttk frame):

https://code.activestate.com/recipes/580717-sortable-megawidget-in-tkinter-like-the-sortable-w/

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