Top-rated recipes by Vasudev Ram

Get names and types of all attributes of a Python module (Python)

2016-10-06T17:21:42-07:00

Python recipe 580705 by Vasudev Ram (documentation, introspection, modules, reflection, type).

This recipe shows how to get the names and types of all the attributes of a Python module. This can be useful when exploring new modules (either built-in or third-party), because attributes are mostly a) data elements or b) functions or methods, and for either of those, you would like to know the type of the attribute, so that, if it is a data element, you can print it, and if it is a function or method, you can print its docstring to get brief help on its arguments, processsing and outputs or return values, as a way of learning how to use it.

The code for the recipe includes an example call to it, at the end of the code. Note that you first have to import the modules that you want to introspect in this way.

Unix tee-like functionality via a Python class (Python)

2017-03-31T14:30:30-07:00

Python recipe 580767 by Vasudev Ram (cli, command, commandline, linux, python, tee, unix, utilities, windows).

The Unix tee commmand, when used in a command pipeline, allows you to capture the output of the preceding command to a file or files, while still sending it on to standard output (stdout) for further processing via other commands in a pipeline, or to print it, etc.

This recipe shows how to implement simple tee-like functionality via a Python class. I do not aim to exactly replicate the functionality of the Unix tee, only something similar.

More details and sample output here:

https://jugad2.blogspot.in/2017/03/a-python-class-like-unix-tee-command.html

Easily create a Python REPL in Python (Python)

2016-10-31T21:53:30-07:00

Python recipe 580712 by Vasudev Ram (code_module, dynamic, evaluation, read_eval_print_loop, repl).

This recipe shows how to easily create a Python REPL (Read-Eval-Print Loop) in Python itself. This can allow the user to interact with a running Python program, including typing in Python statements at the REPL prompt, defining functions, using and changing variables that were set before the interaction started, and those variables modified during the interaction, will persist in the memory of the program, for any use, even after the interaction is over, as long as the program continues to run.

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.

Classifying characters using nested conditional expressions (Python)

2017-04-27T21:26:00-07:00

Python recipe 580792 by Vasudev Ram (characters, classification, conditional_expressions, expressions, join, lambda, map).

Python has a feature called conditional expressions, similar to C's ternary operator. For example:

print n, 'is odd' if n % 2 == 1 else 'is even'

Here, the conditional expression is this part of the print statement above:

'is odd' if n % 2 == 1 else 'is even'

This expression evaluates to 'is odd' if the condition after the if keyword is True, and evaluates to 'is even' otherwise.

The Python Language Reference section for conditional expressions shows that they can be nested. This recipe shows that we can use nested conditional expressions (within a return statement in a user-defined function) to classify characters into lowercase letters, uppercase letters, or neither.

It also shows how to do the same task using map, lambda and string.join, again with a nested conditional expression, but without using return or a user-defined function.

Implementing class-based callbacks in Python (Python)

2017-04-20T23:34:50-07:00

Python recipe 580788 by Vasudev Ram (callbacks, classes, functions, methods, objects, programming, python).

This is a follow-on to this recently posted recipe:

Implementing function-based callbacks in Python: https://code.activestate.com/recipes/580787-implementing-function-based-callbacks-in-python/?in=user-4173351

This new recipe shows how to create and use callbacks in Python, using classes with methods, instead of plain functions, as was done in the recipe linked above. All other points such as reasons and benefits for using callbacks, are more or less the same as mentioned in the previous recipe, except that class instances can carry state around, so to that extent, the two approaches are different.

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

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

A simple Unix shell utility to save cleaned-up man pages as text (Bash)

2017-03-25T14:12:25-07:00

Bash recipe 580766 by Vasudev Ram (bash, documentation, man, script, shell, utilities, utility).

It's a shell script that lets you save the man pages for one or more Unix commands, system calls or other topics, to text files, after cleaning up the man command output to remove formatting meant for emphasis, printing, etc.

More information here:

https://jugad2.blogspot.in/2017/03/m-unix-shell-utility-to-save-cleaned-up.html

Show OS error codes and messages from the os.errno module (Python)

2017-03-01T17:18:23-08:00

Python recipe 580759 by Vasudev Ram (commandline, introspection, libraries, python, unix, utilities, windows).

This recipe is a simple Python introspection utility that displays the defined OS error codes and messages (that Python knows about) from the os.errno module. It works for both Python 2 and Python 3. For each kind of OS error defined in Python, it will display a serial number, the error code, and the corresponding error name, and English error message. E.g. the first few lines of its output are shown below:

$ py -2 os_errno_info.py

Showing error codes and names

from the os.errno module:

Python sys.version: 2.7.12

Number of error codes: 86

Idx Code Name Message

0 1 EPERM Operation not permitted

1 2 ENOENT No such file or directory

2 3 ESRCH No such process

3 4 EINTR Interrupted function call

4 5 EIO Input/output error

More information, full output and other details are available here:

https://jugad2.blogspot.in/2017/03/show-error-numbers-and-codes-from.html

A simple text file pager in Python (Python)

2017-02-10T21:34:45-08:00

Python recipe 580755 by Vasudev Ram (command, commandline, pagination, paging, python, text, utilities, windows).

This recipe shows how to create a simple text file pager in Python. It allows you to view text content a page at a time (with a user-definable number of lines per page). Like standard Unix utilities, it can either take a text file name as a command-line argument, or can read the text from its standard input, which can be redirected to come from a file, or to come from a pipe. The recipe is for Windows only, though, since it uses the msvcrt.getch() function, which is Windows-specific. However, the recipe can be modified to work on Unix by using things like tty, curses, termios, cbreak, etc.

More details here:

https://jugad2.blogspot.in/2017/02/tp-simple-text-pager-in-python.html

Find the arity of a Python function (Python)

2017-01-30T14:09:47-08:00

Python recipe 580753 by Vasudev Ram (functions, introspection, python, python2, reflection).

This recipe shows how to find the arity of a given Python function. The arity of a function is the number of arguments the function takes. The recipe uses the inspect module of Python.

More details and sample output (including some limitations) here:

https://jugad2.blogspot.in/2017/01/finding-arity-of-python-function.html

Classifying letters as vowels or consonants and counting their frequencies (Python)

2017-01-17T20:05:10-08:00

Python recipe 580749 by Vasudev Ram (assertions, comprehension, dict, dictionaries, dict_comp, python, python2, tuple, unpack).

This recipe shows how to take a string as input and classify the characters in it as vowels, consonants or neither. The frequency of each vowel is calculated and the frequency of all the consonants in total is calculated. The program logic is fairly simple, and uses a dictionary comprehension and a dict; the more interesting thing about it, is that it illustrates 8 Python language features in under 35 lines of code.

More details and sample output here:

https://jugad2.blogspot.in/2017/01/classifying-letters-and-counting-their.html

Two quick functions for object introspection (Python)

2017-01-14T22:35:17-08:00

Python recipe 580747 by Vasudev Ram (attributes, debugging, functions, introspection, methods, objects, reflection).

This recipe shows two quick-and-clean :) utility functions for introspection of Python objects. They are meant to be used while working interactively in the reular Python shell or in the IPython shell. Both of them display attributes of any given object passed as the argument. The first function displays all attributes. The second function only displays atttributes that do not begin and end with a double underscore, so as to filter out "dunder" methods a.k.a. "special" methods - like __len__, __str__, __repr__, etc. The first function - oa(o) , where o is some object - does the same as dir(o), but is useful - in IPython - because, dir(o) output will scroll off the screen if the output is long, since it prints the attributes vertically, one per line, while oa(o) prints them horizontally, so has less chance of the output scrolling off, and the output also occupies fewer lines on the screen, so is easier to scan quickly. The second function - oar(o) - is like oa(o), but filters out attribute names that begin and end with a dunder. So it is useful in both IPython and Python.

More information and outputs here:

https://jugad2.blogspot.in/2017/01/two-simple-python-object-introspection.html

A utility like Unix seq (command-line), in Python (Python)

2017-01-08T17:48:57-08:00

Python recipe 580744 by Vasudev Ram (bash, command, commandline, linux, script, seq, sequence, shell, unix, utilities, utility).

This recipe shows how to create a utility like Unix seq (command-line), in Python. seq is described here:

https://en.wikipedia.org/wiki/Seq_(Unix)

but briefly, it is a command-line utility that takes 1 to 3 arguments (some being optional), the start, stop and step, and prints numbers from the start value to the stop value, on standard output. So seq has many uses in bigger commands or scripts; a common category of use is to quickly generate multiple filenames or other strings that contain numbers in them, for exhaustive testing, load testing or other purposes. A similar command called jot is found on some Unix systems.

This recipe does not try to be exactly the same in functionality as seq. It has some differences. However the core functionality of generating integer sequences is the same (but without steps other than 1 for the range).

More details and sample output are here:

https://jugad2.blogspot.in/2017/01/an-unix-seq-like-utility-in-python.html

The code is below.

Give Python code a web plus command-line interface with hug (Python)

2017-01-05T16:57:15-08:00

Python recipe 580742 by Vasudev Ram (cli, commandline, hug, library, python, python3, user_interface, web, web_server).

This recipe shows how to take a Python function and wrap it with both a web and a command-line interface, somewhat easily, using the hug Python library. The example used shows how to wrap a function that uses the psutil library to get information on disk partitions. So you can see the disk partition info either via the web browser or the command line. The code for the recipe is shown below. It is also possible to wrap multiple functions in the same Python file, and expose all of them via both the web and the command-line.

More information and multiple sample outputs are available here:

https://jugad2.blogspot.in/2017/01/give-your-python-function-webcli-hug.html

A command-line musical alarm clock (Python)

2016-12-30T19:06:32-08:00

Python recipe 580739 by Vasudev Ram (alarm, audio, clock, multimedia, music, playsound, python, time, utilities, utility).

This is a simple musical alarm clock in Python. You pass a command-line argument specifying the time in minutes after which the alarm should go off. When that time arrives, it plays a musical sound.

Get disk partition information with psutil (cross-platform) (Python)

2016-12-23T18:05:41-08:00

Python recipe 580737 by Vasudev Ram (device, disk, file_system, psutil, python, sysadmin, system).

This is a recipe that shows how to easily get disk partition information, in a cross-platform manner (for the supported OSes), from your computer's operating system, using the psutil library for Python.

[xtopdf] Publish Delimiter-Separated Values (DSV data) to PDF (Python)

2016-12-17T19:08:33-08:00

Python recipe 580736 by Vasudev Ram (commandline, csv, data, files, formats, pdf, pdf_generation, python, tsv, utilities, xtopdf).

This recipe shows how to publish delimiter-separated values (a commonly used tabular data format) to PDF, using the xtopdf toolkit for PDF creation. It lets the user specify the delimiter via one of two command-line options - an ASCII code or an ASCII character. As Unix filters tend to do, it can operate either on standard input or on input filenames given as command-line arguments. In the case of multiple inputs via files, each input goes to a separate PDF output file.

Simulate C's switch statement (Python)

2016-12-11T16:28:50-08:00

Python recipe 580730 by Vasudev Ram (c, features, language, python, switch).

This recipe shows a Python construct that can behave somewhat like C's switch statement. It is not a perfect one-to-one simulation. But it does have some of the features of the C switch. One feature not supported is the fall-through feature in C's switch.

Convert wildcard text files to PDF with xtopdf (e.g. report*.txt) (Python)

2016-12-06T20:37:30-08:00

Python recipe 580727 by Vasudev Ram (conversion, files, globbing, patterns, pdf, pdfwriter, pdf_generation, text_processing, wildcard, xtopdf).

This recipe shows how to convert all text files matching a filename wildcard to PDF, using the xtopdf PDF creation toolkit. For example, if you specify report.txt as the wildcard, all files in the current directory that match report.txt, will be converted to PDF, each in a separate PDF file. The original text files are not changed.

Here is a guide to installing and using xtopdf:

http://jugad2.blogspot.in/2012/07/guide-to-installing-and-using-xtopdf.html

More details on running the program, and sample output, are available here:

http://jugad2.blogspot.in/2016/12/xtopdf-wildcard-text-files-to-pdf-with.html