Popular recipes tagged "meta:min_python_3=1"

Equally-spaced numbers (linspace) (Python)

2015-01-12T22:16:37-08:00

Python recipe 579000 by Andrew Barnert (float, linspace, range, spread).

An equivalent of numpy.linspace, but as a pure-Python lazy sequence.

Like NumPy's linspace, but unlike the spread and frange recipes listed here, the num argument specifies the number of values, not the number of intervals, and the range is closed, not half-open.

Although this is primarily designed for floats, it will work for Fraction, Decimal, NumPy arrays (although this would be silly) and even datetime values.

This recipe can also serve as an example for creating lazy sequences.

See the discussion below for caveats.

Compute Memory footprint of an object and its contents (Python)

2012-11-23T23:57:31-08:00

Python recipe 577504 by Raymond Hettinger (memory, sizeof). Revision 3.

Recursive version sys.getsizeof(). Extendable with custom handlers.

Function guards for Python 3 (Python)

2016-05-01T13:11:05-07:00

Python recipe 580658 by Dmitry Dvoinikov (call, decorator, dispatch, function, guard).

This module implements a function guard - facility to redirect the the call to one of several function implementations at run time based on the actual call arguments.

Wrap each of the identically named functions in a @guard decorator and provide a _when parameter with a default value set to guarding expression.

See samples at the top of the module.

Yet another singleton pattern in Python using class decorators (Python)

2015-08-11T19:14:45-07:00

Python recipe 579090 by David Hollman (patterns, python, singleton). Revision 8.

Another pattern for creating singleton instances of classes in Python.

Amazon SNS handler for the logging module (Python)

2014-11-06T17:32:26-08:00

Python recipe 578956 by Andrea Corbellini (aws, logging, sns). Revision 2.

This is a handler for the standard logging module that sends notifications to the Amazon Simple Notification Service.

You can use it like so:

logging.config.dictConfig({
    'version': 1,
    'disable_existing_loggers': False,
    'formatters': {
        'verbose': {
            'format': '%(levelname)s %(asctime)s %(module)s %(process)d '
                      '%(thread)d %(message)s',
        },
        'simple': {
            'format': '%(levelname)s %(message)s',
        },
    },
    'handlers': {
        'sns': {
            'level': 'INFO',
            'class': 'SNSHandler',
            'formatter': 'verbose',
            'topic_arn': 'YOUR SNS TOPIC ARN',
        },
    },
    'loggers': {
        'YOUR MODULE': {
            'handlers': ['sns'],
            'level': 'INFO',
            'propagate': True,
        },
    },
}

Call out to an external editor (Python)

2014-09-01T18:26:51-07:00

Python recipe 578926 by Steven D'Aprano (editing, editor, external, text). Revision 2.

Here's a function that lets you use Python to wrap calls to an external editor. The editor can be an command line editor, like venerable old "ed", or something more powerful like nano, vim or emacs, and even GUI editors. After the editor quits, the text you typed in the editor is returned by the function.

A simple example, using the (rather cryptic) 'ed' editor on Linux. For the benefit of those unfamiliar with 'ed', I have annotated the editor session with comments.

>>> status, text = edit('ed')
0                        ## ed prints the initial number of lines
a                        ## start "append" mode
Hello World!
Goodbye now
.                        ## stop appending
w                        ## write the file to disk
25                       ## ed prints the number of bytes written
q                        ## quit ed and return to Python
>>> status
0
>>> print text
Hello World!
Goodbye now

Strongly connected components of a directed graph. (Python)

2013-04-03T19:30:32-07:00

Python recipe 578507 by Mark Dickinson (connected, directed, graph, strong, tarjan). Revision 3.

Two linear-time algorithms for finding the strongly connected components of a directed graph. strongly_connected_components_tree implements (a variant of) Tarjan's well-known algorithm for finding strongly connected components, while strongly_connected_components_path implements a path-based algorithm due (in this form) to Gabow.

Edit: I added an iterative function strongly_connected_components_iterative; this is a direct conversion of strongly_connected_components_path into iterative form. It's therefore safe to use on high-depth graphs, without risk of running into Python's recursion limit.

Integer square root function (Python)

2011-08-04T05:29:16-07:00

Python recipe 577821 by Steven D'Aprano (integer, isqrt, math, mathematics, maths, root, square).

The integer square root function, or isqrt, is equivalent to floor(sqrt(x)) for non-negative x. For small x, the most convenient way to calculate isqrt is by calling int(x**0.5) or int(math.sqrt(x)), but if x is a large enough integer, the sqrt calculation overflows.

You can calculate the isqrt without any floating point maths, using just pure integer maths, allowing the function to operate with numbers far larger than possible with floats:

>>> n = 1234567*(10**1000)
>>> n2 = n*n
>>> math.sqrt(n2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OverflowError: long int too large to convert to float
>>> isqrt(n2) == n
True

Yahoo Stock Information (Python)

2012-08-25T17:16:47-07:00

Python recipe 577989 by Alexander James Wallar (computation, corey_goldberg, finance, information, python, realtime, stock, yahoo). Revision 3.

This recipe is solely due to the programming of Corey Goldberg (corey@goldb.org). The only thing I did to it was make it into a class. I thought that by uploading it here that more people would come across it and more people could use it. It is really good. It gives you stock information.

Generate equally-spaced floats (Python)

2011-09-24T18:49:39-07:00

Python recipe 577878 by Steven D'Aprano (float, range, spread).

Generating a list of equally-spaced floats can surprising due to floating point rounding. See, for example, the recipe for a floating point range. One way of avoiding some surprises is by changing the API: instead of specifying a start, stop and step values, instead use a start, stop and count:

>>> list(spread(0.0, 2.1, 7))
[0.0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8]

Like frange spread takes an optional mode argument to select whether the start and end values are included. By default, start is included and end is not, and exactly count values are returned.

(Yet another) Assignment in expression Recipe (Python)

2011-12-17T20:03:26-08:00

Python recipe 577987 by harish anand (expression, shortcuts). Revision 3.

Python does not support assignment in if and while statements such as "if (x=func()):". This is an attempt to bring similar functionality to python by injecting bytecode to all functions and methods in a module. This recipe is inspired from recipes 66061, 202234 and 277940.

Selective directory walking (Python)

2011-10-20T05:05:39-07:00

Python recipe 577913 by Nick Coghlan (directories, files, globbing). Revision 2.

Python's os.walk() standard library iterator is useful if you want to walk an entire directory tree, but you're on your own when it comes to implementing name filtering and recursive depth limiting on top of it.

This recipe supports these features with an interface that is just as convenient as the underlying os.walk() API, while being significantly more powerful.

Rsync Algorithm (Python)

2011-01-09T16:32:22-08:00

Python recipe 577518 by Eric Pruitt (algorithm, delta, diff, patch, python3, rsync). Revision 4.

This is a pure Python implementation of the rsync algorithm. On my desktop (3.0GHz dual core, 7200RPM), best case throughput for target file hash generation and delta generation is around 2.9MB/s. Absolute worst case scenario (no blocks in common) throughput for delta generation is 200KB/s to 300KB/s on the same system.

Tested in Python 2.5, 2.6, and 3.1. In 2.7, io.BufferedReader should yield the best throughput. On all other versions use __builtin__.open.

format_iter: easy formatting of arbitrary iterables (Python)

2011-08-16T11:44:59-07:00

Python recipe 577845 by Nick Coghlan (formatting, strings).

The format_iter recipe defines a simple wrapper around str.join and str.format that makes it easy to format an arbitrary iterable with a specified format string and item separator.

Search sequences for sub-sequence (Python)

2011-08-19T05:17:00-07:00

Python recipe 577850 by Steven D'Aprano (find, searching, sequence, string, sublist, substring).

The list and tuple index() method and in operator test for element containment, unlike similar tests for strings, which checks for sub-strings:

>>> "12" in "0123"
True
>>> [1, 2] in [0, 1, 2, 3]
False

These two functions, search and rsearch, act like str.find() except they operate on any arbitrary sequence such as lists:

>>> search([1, "a", "b", 2, 3], ["b", 2])
2

Bloom Filter (Python)

2011-05-05T07:25:01-07:00

Python recipe 577686 by Sundar Srinivasan (big_table, bloom_filter, sets, spelling_checker). Revision 2.

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

Bitmap Maker (Python)

2011-04-21T13:08:46-07:00

Python recipe 577674 by Stephen Chappell (experiment, generator, images, proof_of_concept, test).

A friend and I were discussing the possibility of creating every possible image that is 800x600x24 (800 pixels wide by 600 pixels tall and using 24-bit color). This recipe is a proof-of-concept program showing what is possible with just a 2x2 image using 15 different colors (yielding a total of 50,625 images when run). In terms of the original thought experiment, a total of 16777216 ** 480000 images should be possible given the 800x600x24 specifications (or 1 << 11520000 in binary). In base 10 that is 10 ** 3467865.55 and shows that there are an enormous number of possible states that a 800x600 canvas can take.

If you have any comments or wish to down-vote this recipe, please provide your insight as to what could be improved upon and how you would go about fixing any problems that you might find.

Convert a youtube transcript in srt subtitle (Python)

2010-11-12T01:59:53-08:00

Python recipe 577459 by Ginko (converter, srt, transcript, youtube).

A quick and dirty script to convert youtube's transcripts (xml format) to .srt subtitle files.

To download youtube's transcript, use this url: http://video.google.com/timedtext?lang=en&v=VIDEO_ID (replace "VIDEO_ID" by the ID which is in the video URL).

You can easily use this converter in a script which could download the transcript by importing it and then call the main function.

Sleepsort with processes and pipes (Python)

2011-06-17T02:37:58-07:00

Python recipe 577758 by Benjamin Peterson (process, sorting, unix). Revision 2.

Sleepsort is a sorting algorithm that uses the system sleep syscall in a very creative fashion.

This is the same algorithm as recipe 577756 but using *nix processes instead of threads.

Python Tkinter Canvas Rectangle Selection Box (Python)

2010-10-01T02:17:50-07:00

Python recipe 577409 by Sunjay Varma (canvas, rectangle, selection, tkinter).

A simple, yet effective rectangle selection box. :)

Works with a tkinter canvas! Just add the class and set it up like in the example code. The cross heir was my own touch, the RectTracker only draws a box.

Have fun! And please don't just vote down, post what you don't like if you don't like it.