Popular recipes by Paddy McCarthy

Shoelace Formula for polygonal area (Python)

2017-07-17T05:53:45-07:00

Python recipe 580812 by Paddy McCarthy (2d, area).

Copied, by author from "Paddy3118 Go deh!: Python investigation of the Shoelace Formula for polygonal area http://paddy3118.blogspot.com/2017/07/python-investigation-of-shoelace.html#ixzz4n43Dqhaa " Where there is more meat on the bone (under a different license though).

Generate the parity or sign of a permutation (Python)

2012-07-28T07:21:49-07:00

Python recipe 578227 by Paddy McCarthy (determinants, mathematics, matrix, permutations).

The parity of a given permutation is whether an odd or even number of swaps between any two elements are needed to transform the given permutation to the first permutation.

The sign of the permutation is +1 for an even parity and -1 for an odd parity.

This python function returns the sign of a permutation of all the integers 0..N. When the program is run it shows the sign of permutations as generated by the standard function itertools.permutations.

The function uses a modified selection sort to compute the parity.

Alternatve generation of the parity or sign of a permutation (Python)

2012-08-07T08:45:23-07:00

Python recipe 578236 by Paddy McCarthy (determinants, mathematics, matrix, permutations).

Although Recipe 578227 was straight-forward to derive, I came across this Stack Overflow answer that gives another method for generating the sign based on comparing the perm and the sorted perm.

Topological Sort (Python)

2010-09-28T19:22:27-07:00

Python recipe 577413 by Paddy McCarthy (algorithm, sorting, topological).

Given items that depend on other items, a topological sort arranges items in order that no one item precedes an item it depends on. In this example items are strings and dependencies are expressed in a dictionary whose keys are items and whose values are a set of dependent items. Note that the dict may contain self-dependencies (which are ignored), and dependent items that are not also dict keys, such as the item 'ieee'.

McCarthy's amb operator in Python (Python)

2010-08-23T22:41:53-07:00

Python recipe 577368 by Paddy McCarthy (declarative, style).

From reading about amb it seems that it allows for a declaritive style of programming where the one amb "operator" can * Set the ranges of variables * Set a constraint function * And iterate over all solutions

(See http://paddy3118.blogspot.com/2010/08/mccarthys-amb-operator-in-python.html for a more descriptive intro).

Extension to Python 3 Counter class (Python)

2010-08-18T21:02:41-07:00

Python recipe 577362 by Paddy McCarthy (bag, counter, multiset, python). Revision 3.

Adds symmetric difference and cartesian product to the Counter class. I had a use case for the former and Raymond H. asked about the latter so I coded the latter from its Wikipedia description.

Luhn test for credit card numbers (Python)

2010-03-01T22:19:44-08:00

Python recipe 577078 by Paddy McCarthy (algorithms). Revision 2.

Implements the Luhn test succinctly.

SEDOL code validator and checksum generator (Python)

2008-08-03T01:00:51-07:00

Python recipe 576405 by Paddy McCarthy (security).

Will check SEDOL numbers as well as generate a SEDOL checksum digit.

Another generator for an arbitrary number of 'for' loops (Python)

2007-01-31T13:31:26-08:00

Python recipe 502199 by Paddy McCarthy (algorithms).

Saw recipe 502194 and wondered if I could do similar. I initially came up with function comb that enumerates all combinations. I wanted a generator however and so abandoned that approach for comb2 which is a little more complex.

Optimising Regression Testing on COmpute Farms (Python)

2004-04-25T18:53:23-07:00

Python recipe 280030 by Paddy McCarthy (algorithms). Revision 2.

Collects statistics on different algorithms for grouping thousands of tests for execution on a compute farm where you are limited to much less job slots, (tens).