Implementing function-based callbacks in Python (Python)

2017-04-19T18:03:11-07:00

Python recipe 580787 by Vasudev Ram (callback, function, functions, python, techniques).

This recipe shows a simple way of implementing callbacks in Python. There are a few ways this can be done. The way shown here uses a simple function-based approach.

In a nutshell, a callback can be informally described like this: function a calls function b, and wants to make b run a specific independent chunk of code at some point during b's execution. We want to be able to vary which chunk of code gets called in different calls to b, so it cannot be hard-coded inside b. So function a passes another function, c, to b, as one argument, and b uses that parameter c to call the functionality that a wants b to call. (Function b may pass some parameters to the function represented by c, when it calls it. These could be either internally generated, passed from a, or a combination of both). So, by changing the value of the function c that gets passed to b (on different calls to b), a can change what chunk of code b calls.

More details and full code, description and output here:

https://jugad2.blogspot.in/2017/04/implementing-and-using-callbacks-in.html

Discrete PID Controller (Python)

2015-12-18T20:59:43-08:00

Python recipe 577231 by Caner (controller, derivative, discrete, integral, pid, proportional, python).

The recipe gives simple implementation of a Discrete Proportional-Integral-Derivative (PID) controller. PID controller gives output value for error between desired reference input and measurement feedback to minimize error value. More information: http://en.wikipedia.org/wiki/PID_controller

For new version please check: https://github.com/ivmech/ivPID

Log watcher (tail -F *.log) (Python)

2014-04-04T15:54:03-07:00

Python recipe 577968 by Giampaolo Rodolà (color, log, logging, monitor, python, rotate, rotations, tail). Revision 10.

A python class which "watches" a directory and calls a callback(filename, lines) function every time one of the files being watched gets written, in real time.

Practically speaking, this can be compared to "tail -F *.log" UNIX command, but instead of having lines printed to stdout a python function gets called.

Similarly to tail, it takes care of "watching" new files which are created after initialization and "unwatching" those ones which are removed in the meantime. This means you'll be able to "follow" and support also rotating log files.

History

rev5 (2013-04-05):
- sizehint parameter
rev4 (2013-03-16):
- python 3 support (also dropped support for python <= 2.5)
- windows support
- unit tests
- main class can also be used as a context manager
rev3 (2012-01-13): initial release

Simple command-line alarm clock in Python (Python)

2015-10-25T18:27:27-07:00

Python recipe 579117 by Vasudev Ram (alarm, clock, commandline, linux, python, time, unix, windows).

This recipe shows how to create a simple alarm clock in Python, that can be run from the command line in a terminal. It lets you specify the alarm time in minutes as a command line argument, and prints a wake-up message and beeps a few times, after that time arrives. You can use 0 for the minutes to test it immediately, including to adjust the volume using your speaker controls.

Basic threaded Python TCP server (Python)

2012-09-19T17:59:01-07:00

Python recipe 578247 by Luis Martin Gil (python, server, tcp, thread). Revision 3.

TCP provides reliable, ordered delivery of a stream of bytes from a program on one computer to another program on another computer. Sometimes you need a quick deployment of a TCP server and here I bring to you a Python 2.* snippet of a threaded Python server.

Python text-to-speech with pyttsx (Python)

2014-03-02T21:35:15-08:00

Python recipe 578839 by Vasudev Ram (python, pyttsx, speech, text_to_speech).

This recipe shows how to generate computer speech from text using the pyttsx Python library. Text-to-speech, or speech synthesis, has many useful applications.

Convert Microsot Excel (XLSX) to PDF with Python and xtopdf (Python)

2015-11-22T22:15:25-08:00

Python recipe 579128 by Vasudev Ram (excel, formats, openpyxl, pdf, python, xlsx, xtopdf).

This recipe shows how the basics of to convert the text data in a Microsoft Excel file (XLSX format) to PDF (Portable Document Format). It uses openpyxl to read the XLSX file and xtopdf to generate the PDF file.

Python script to create a header for Python scripts (Python)

2011-10-02T15:45:11-07:00

Python recipe 577846 by userend (2, auto, create, emacs, header, linux, python, script, vim). Revision 5.

This will create a header for a Python script. It is a nice way keep a track of what your script does and when it was created, the author of the script, etc..

Update: Now, it will automatically open with one of the two most popular editors, Vim or Emacs! This script has been updated from the second version to replace spaces with underscores in the title, to convert uppercase to lowercase. It also checks to see if there is a script with the same name in the current working directory so it will not overwrite another file. Please leave comments and suggestions.

Disk usage (Python)

2012-10-06T15:33:40-07:00

Python recipe 577972 by Giampaolo Rodolà (disk, python, python3, space, statistics, usage). Revision 6.

Provides disk usage statistics (total, used and free disk space) about a given path.

This recipe was initially developed for psutil:

http://code.google.com/p/psutil/issues/detail?id=172

...and then included into shutil module starting from Python 3.3:

The recipe you see here is a modified version of the latter one in that the Windows implementation uses ctypes instead of a C extension module. As such it can be used with python >= 2.5.

Simple Back-propagation Neural Network in Python source code (Python)

2012-05-30T17:09:49-07:00

Python recipe 578148 by David Adler (back, back_propagation, neural, neural_network, propagation, python).

This is a slightly different version of this http://arctrix.com/nas/python/bpnn.py

Simple Morse Code Translator in Python (Python)

2013-01-08T18:02:46-08:00

Python recipe 578407 by Captain DeadBones (morse_code, python).

This is a basic Morse Code Generator in python. I wrote it for an article I put together Morse Code and Dictionaries in Python

Bisection Method in Python (Python)

2013-01-16T16:37:33-08:00

Python recipe 578417 by Captain DeadBones (bisect, mathematics, python).

This is a quick way to do bisection method in python. I wrote his code as part of an article, How to solve equations using python

Genetic Algorithm in Python source code - AI-Junkie tutorial (Python)

2012-06-19T12:59:13-07:00

Python recipe 578128 by David Adler (algorithm, artificial, genetic, network, neural, python). Revision 5.

A simple genetic algorithm program. I followed this tutorial to make the program http://www.ai-junkie.com/ga/intro/gat1.html.

The objective of the code is to evolve a mathematical expression which calculates a user-defined target integer.

KEY:

chromosome = binary list (this is translated/decoded into a protein in the format number --> operator --> number etc, any genes (chromosome is read in blocks of four) which do not conform to this are ignored.

protein = mathematical expression (this is evaluated from left to right in number + operator blocks of two)

output = output of protein (mathematical expression)

error = inverse of difference between output and target

fitness score = a fraction of sum of of total errors

OTHER:

One-point crossover is used.

I have incorporated elitism in my code, which somewhat deviates from the tutorial but made my code more efficient (top ~7% of population are carried through to next generation)

Validate data easily with JSON Schema (Python)

2015-12-06T21:23:48-08:00

Python recipe 579135 by Vasudev Ram (data, json, jsonschema, python, python2).

This recipe shows how to use the jsonschema Python library, which implements the JSON Schema specification, to easily validate your Python data. It sends good output to stdout and bad output to stderr, for demo purposes.

jsonschema Python library: https://pypi.python.org/pypi/jsonschema

JSON Schema: http://json-schema.org/

Super Simple Sudoku Solver in Python source code (Python)

2012-06-23T14:56:05-07:00

Python recipe 578140 by David Adler (algorithm, python, recursive, recurssion, sodoku, sudoku). Revision 5.

A simple algorithm which uses a recursive function to solve the puzzle.

THE ALGORITHM

The credit for this algorithm must go to Richard Buckland: http://www.youtube.com/watch?v=bjObm0hxIYY&feature=autoplay&list=PL6B940F08B9773B9F&playnext=1

Takes a partially filled in grid, inserts the min value in a cell (could be a random cell, in this case the first free cell). If the min value is not legal it will increment until the max value is reached (number 9), checking each time if the incremented value is legal in that cell (ie does not clash with any already entered cells in square, col or row). If it is legal, it will call itself (the hasSolution function) thus using this slightly more filled in grid to find a new cell and check which value is legal in this next cell. If no values are legal in the next cell, it will clear the previous grid entry and try incrementing the value.

isLegal = does not conflict with any other numbers in the same row, column or square

Recognizing speech (speech-to-text) with the Python speech module (Python)

2015-10-22T13:09:02-07:00

Python recipe 579115 by Vasudev Ram (language_translation, python, python2, speech_recognition, windows).

This recipe shows how to use the 'speech' (or 'pyspeech' - it seems to have two names) Python library to make the computer recognize what you say and convert it to text. Note: This library did not always give correct results for me, so it may not be advisable to use it in production. Also, the pyspeech site says that the library is no longer being maintained. Use at your own risk.

Convert doc and docx files to pdf (Python)

2014-03-31T18:39:16-07:00

Python recipe 578858 by Fabian Mayer (doc, pdf, python, win32com). Revision 2.

The Script converts all doc and docx files in a specified folder to pdf files. It checks whether the provided absolute path does actually exist and whether the specified folder contains any doc and docx files. It does not travers the directory recursively. The script is not portable and runs only a Windows machine. Based on the experience I made, I recommend closing MS Word before running the script.

Chek if a number is a power of two (Python)

2010-12-23T11:29:38-08:00

Python recipe 577514 by A. Polino (2, check, number, power, python). Revision 2.

Pretty good way to check if a number is a power of two or not.

Decoding Binary Files (Python)

2011-03-15T00:11:10-07:00

Python recipe 577610 by Yony Kochinski (binary, decode, file, python). Revision 2.

One way to read files that contain binary fields is to use the struct module. However, to do this properly one must learn struct's format characters, which may look especially cryptic when sprinkled around the code. So instead, I use a wrapper object that presents a simple interface as well as type names that are more inline with many IDLs.

Merge unique items from multiple lists into a new list (Python)

2016-04-05T18:11:49-07:00

Python recipe 580634 by Johannes S (lists, merge, python, set). Revision 2.

Suppose you have multiple lists. You want to print all unique items from the list. Now, what you could do is merge the lists into one_big_list (e.g., a + b +c), and then iterate over each item in one_big_list, etc. The solution proposed here gets this done faster and in one line of code. How? By using a python set. A python set is a dictionary that contains only keys (and no values). And dictionary keys are, by definition, unique. Hence, duplicate items are weeded out automatically. Once you have the set, you can easily convert it back into a list. As easy as that!

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