Popular recipes by Vasudev Ram

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.

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

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

Simulating an unless (reverse if) statement in Python (Python)

2017-02-23T22:38:50-08:00

Python recipe 580758 by Vasudev Ram (features, if, perl, programming, python, trick).

This recipe shows how to simulate an unless statement (a sort of reverse if, like Perl has), in Python. It is just for fun and as an experiment, not meant for real use, because the effect of unless can easily be got by negating the sense of the condition in an if statement.

More details and output here:

https://jugad2.blogspot.in/2017/02/perl-like-unless-reverse-if-feature-in.html

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

[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.

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

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

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.

Batch conversion of text files to PDF with fileinput and xtopdf (Python)

2016-11-07T20:28:01-08:00

Python recipe 580715 by Vasudev Ram (batch, batchmode, conversion, files, pdf, pdfwriter, python, text, text_processing, utilities, xtopdf).

This recipe shows how to do a batch conversion of the content of multiple text files into a single PDF file, with a) an automatic page break after the content of each text file (in the PDF output), b) page numbering, and c) a header and footer on each page.

It uses the fileinput module (part of the Python standard library), and xtopdf, a Python library for conversion of other formats to PDF.

xtopdf is available here: https://bitbucket.org/vasudevram/xtopdf

and a guide to installing and using xtopdf is here:

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

Here is a sample run of the program:

python BTTP123.pdf text1.txt text2.txt text3.txt

This will read the content from the three text files specified and write it into the PDF file specified, neatly formatted.

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.

Read CSV with D and write it to PDF with Python (Python)

2016-10-26T17:49:00-07:00

Python recipe 580710 by Vasudev Ram (conversion, csv, data, files, formats, pdf, pdf_generation, xtopdf).

This recipe shows how to read data from a CSV file with a D program and write that data to a PDF file with a Python program - all in a single command-line invocation (after writing the individual programs, of course).

It requires the xtopdf toolkit, which you can get from:

https://bitbucket.org/vasudevram/xtopdf

Instructions for installing xtopdf:

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

xtopdf in turn requires the open source version of the ReportLab toolkit, which you can get from:

http://www.reportlab.com/ftp (http://www.reportlab.com/ftp/reportlab-1.21.1.tar.gz)

It also requires the DMD compiler to compile the D program - this was the version used:

DMD32 D Compiler v2.071.2

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

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

Number of bits needed to store an integer, and its binary representation (Python)

2017-03-12T23:10:48-07:00

Python recipe 580762 by Vasudev Ram (binary, formats, integers, numbers, representation, type).

This recipe shows how to find, via Python code, the number of bits needed to store an integer, and how to generate its binary representation. It does this for integers from 0 to 256.

More details and full output here:

https://jugad2.blogspot.in/2017/03/find-number-of-bits-needed-to-store.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.

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

Quick-and-dirty Windows drive detector (Python)

2016-09-20T17:46:37-07:00

Python recipe 580699 by Vasudev Ram (drives, sysadmin, system_programming, utility, windows).

This is a quick-and-dirty Python script to detect the currently available drives on your Windows PC.