Latest recipes by Raymond Hettinger

Auto differentiation (Python)

2016-08-07T22:02:10-07:00

Python recipe 580610 by Raymond Hettinger (autodifferentiation, calculus, descent, gradient, math, optimization, vector). Revision 5.

Directly computes derivatives from ordinary Python functions using auto differentiation. The technique directly computes the desired derivatives to full precision without resorting to symbolic math and without making estimates bases on numerical methods.

The module provides a Num class for "dual" numbers that performs both regular floating point math on a value and its derivative at the same time. In addition, the module provides drop-in substitutes for most of the functions in the math module. There are also tools for partial derivatives, directional derivatives, gradients of scalar fields, and the curl and divergence of vector fields.

Proof-of-concept for a more space-efficient, faster-looping dictionary (Python)

2013-01-17T09:28:24-08:00

Python recipe 578375 by Raymond Hettinger (compact, dictionary). Revision 20.

Save space and improve iteration speed by moving the hash/key/value entries to a densely packed array keeping only a sparse array of indices. This eliminates wasted space without requiring any algorithmic changes.

Colorize Python -- Sourcecode Syntax Highlighting (Python)

2012-07-21T02:46:37-07:00

Python recipe 578178 by Raymond Hettinger (highlighting, syntax). Revision 20.

Generates colorized HTML, ANSI escaped text, or a LaTeX document from Python source code. Useful for publishing or viewing your code in a more readable way.

Pi Circle (Python)

2012-05-13T04:35:46-07:00

Python recipe 578130 by Raymond Hettinger (art, ascii, fun, pi). Revision 5.

Computes Pi to many decimal places and prints the digits in a circle.

Simple tool for simulating classes using closures and nested scopes (Python)

2012-04-11T06:21:18-07:00

Python recipe 578091 by Raymond Hettinger (closure, object, oriented). Revision 9.

Closured-based alternative to normal classes. Allows a faster, cleaner coding style at the expense of some functionality.

Py2.6+ and Py3.0+ backport of Python 3.3's LRU Cache (Python)

2013-03-06T05:38:15-08:00

Python recipe 578078 by Raymond Hettinger (cache, lru). Revision 6.

Full-featured O(1) LRU cache backported from Python3.3. The full Py3.3 API is supported (thread safety, maxsize, keyword args, type checking, __wrapped__, and cache_info). Includes Py3.3 optimizations for better memory utilization, fewer dependencies, and fewer dict lookups.

Simplified LRU Cache (Python)

2013-03-06T06:04:18-08:00

Python recipe 577970 by Raymond Hettinger (cache, lru). Revision 6.

An O(1) LRU cache. Short, sweet, and fast.

Simplified, highly optimized LRU Cache (Python)

2011-12-01T00:57:38-08:00

Python recipe 577969 by Raymond Hettinger (cache, lru). Revision 3.

An O(1) LRU cache. Short, sweet, and fast. No bells and whistles.

Inner Join (Python)

2011-11-01T20:10:34-07:00

Python recipe 577937 by Raymond Hettinger (database, join, sql). Revision 2.

Implemented an SQL style INNER JOIN for two lists of tuples to be joined on a common field.

Fast min/max function (Python)

2011-10-22T18:40:32-07:00

Python recipe 577916 by Raymond Hettinger (minmax, sorting).

Minimizes the number of comparisons to compute the minimum and maximum of a dataset. Uses 1.5 compares for every element, improving on the more obvious solution that does 2 comparisons per element.

Compare speeds of different kinds of access to variables (Python)

2011-08-10T23:54:12-07:00

Python recipe 577834 by Raymond Hettinger (optimization). Revision 5.

Compare speeds of locals, nested scopes, global, builtins, instance variables, and class variables.

Sleepsort (Python)

2011-06-17T05:17:22-07:00

Python recipe 577756 by Raymond Hettinger (sorting, threads). Revision 2.

Funky sort routine to demonstrate Python's threading basics.

Experiment with Kaprekar's routine (Python)

2011-06-12T03:29:01-07:00

Python recipe 577749 by Raymond Hettinger (6174, dot, graph, kaprekar). Revision 2.

Explore the story behind the mysterious number 6174. Generate all possible chains leading to 6174, show their length and their patterns of convergence.

Public Key Encryption (RSA) (Python)

2012-05-12T23:34:22-07:00

Python recipe 577737 by Raymond Hettinger (encryption, inverse, multiplicative, primality_testing, primes, publickey, rsa). Revision 2.

Simple code to create and use public/private keypairs. Accompanied by a rudimentary encoder.

How to use super() effectively -- Python 2.7 version (Python)

2011-06-01T19:19:37-07:00

Python recipe 577721 by Raymond Hettinger (cooperative, inheritance, multiple, next_in_mro, super). Revision 8.

Python's super() provides a unique and amazing capability. It allows subclasses to be written to reorder a chain method calls. The recipe demonstrates all of the tradecraft needed to get super() to do your bidding.

How to use super() effectively (Python)

2011-06-01T19:17:58-07:00

Python recipe 577720 by Raymond Hettinger (cooperative, inheritance, multiple, next_in_mro, super). Revision 8.

Bloom Filter (Python)

2011-06-04T17:44:21-07:00

Python recipe 577684 by Raymond Hettinger (big_table, bloom_filter, sets, spelling_checker, spell_checker). Revision 18.

Space efficient, probabilistic set membership tester. Has no False Negatives but allows a rare False Positive.

Dirt simple map/reduce (Python)

2011-05-15T16:46:55-07:00

Python recipe 577676 by Raymond Hettinger (analysis, crosstab, functional, map_reduce, pivot_table, statistics). Revision 9.

Simple tool for analyzing datasets.

Amazing estimation of Pi using the Mandlebrot set (Python)

2011-02-20T07:34:56-08:00

Python recipe 577584 by Raymond Hettinger (approximation, mandlebrot, pi, strange).

Miraculously, you can estimate π just by counting the number of iterations for a point near the neck to escape. The method has a rigorous error bound.

Compare algorithms for heapq.smallest (Python)

2011-12-25T23:41:23-08:00

Python recipe 577573 by Raymond Hettinger (algorithms, benchmark, heaps, performance). Revision 3.

General purpose technique for counting comparisons in various searching and sorting applications.