Popular recipes tagged "meta:loc=39"

Python-C-Interface: Check whether a given dictionary contains only valid keys (C)

2017-05-06T20:53:54-07:00

C recipe 580799 by Jorj X. McKie (c_interface, python).

This function is given a Python dictioanry and a list of string / unicode values. It will check whether all dictionary keys occur in this list and will return 1 (true) or 0 (false).

Python add/set attributes to list (Python)

2015-09-29T16:28:46-07:00

Python recipe 579103 by webby1111 (attributes, class, dictionary, list, subclass). Revision 3.

Python Attribute List

Add/set attributes to python lists.

A google search for "add attributes to python lists" yields no good stackoverflow answer, hence the need for this.

Useful for machine learning stuff where you need labeled feature vectors.

This technique can be easily adapted for other built-ins (e.g. int).

The Problem

a = [1, 2, 4, 8]
a.x = "Hey!" # AttributeError: 'list' object has no attribute 'x'

The Solution

a = L(1, 2, 4, 8)
a.x = "Hey!"
print a       # [1, 2, 4, 8]
print a.x     # "Hey!"
print len(a)  # 4

# You can also do these:
a = L( 1, 2, 4, 8 , x="Hey!" )                 # [1, 2, 4, 8]
a = L( 1, 2, 4, 8 )( x="Hey!" )                # [1, 2, 4, 8]
a = L( [1, 2, 4, 8] , x="Hey!" )               # [1, 2, 4, 8]
a = L( {1, 2, 4, 8} , x="Hey!" )               # [1, 2, 4, 8]
a = L( [2 ** b for b in range(4)] , x="Hey!" ) # [1, 2, 4, 8]
a = L( (2 ** b for b in range(4)) , x="Hey!" ) # [1, 2, 4, 8]
a = L( 2 ** b for b in range(4) )( x="Hey!" )  # [1, 2, 4, 8]
a = L( 2 )                                     # [2]

Jump (Batch)

2013-08-08T09:18:31-07:00

Batch recipe 578627 by greg zakharov (dirjump, jscript, regjump).

How does it work? Just input registry key or folder path after script name. Note that script works well on WinXP and has not been tested on higher Win systems. Also you should know that if regedit has been launched then when you trying access another key it always starts with another window of regedit. Explorer has the same behaviour with this script. You can jump to HKCR, HKCU and HKLM branches but if you need more, please edit script manually :) For folders jump you should input full or relative path. For example: jump \doc or jump . or jump E:\fotos

Peek at Python value stack (Python)

2013-01-08T22:15:21-08:00

Python recipe 578412 by Dima Tisnek (python, python2, stack).

Poking at value stack, a.k.a. evaluation stack is not allowed in Python, however everything is doable with ctypes.

I think this could be useful in debugging complex statements.

Saving a Tkinter canvas image or animation using PIL (Python)

2012-03-05T04:09:00-08:00

Python recipe 578063 by J W J (borderless, canvas_save, imagegrab). Revision 2.

Demonstrates saving an animation done on Tkinter canvas as a series of jpeg images

Multidimensional arrays (Ruby)

2012-11-19T08:43:11-08:00

Ruby recipe 578338 by greg zakharov (array, ironruby, multidimensional).

The next example shows how to create rectangular and jagged arrays.

FeatureClassRandomizer (Python)

2012-08-07T15:35:23-07:00

Python recipe 578237 by Dale Lindeman (randomization, random_number).

Generates a randomized list of unique IDs and iteratively assigns values to features in a featureclass.

Python Viewer (Python)

2012-07-02T22:29:27-07:00

Python recipe 578181 by Stephen Chappell (archive, cgi, old, viewer).

This was a CGI experiment from many years ago for viewing Python files on a server. This is committed for archival to be run under Python 2.5 or later versions.

subtract or add a month to a datetime.date or datetime.datetime (Python)

2010-06-25T18:41:19-07:00

Python recipe 577274 by Trent Mick (date, datetime, month).

Adding or subtracting a month to a Python datetime.date or datetime.datetime is a little bit of a pain. Here is the code I use for that. These functions return the same datetime type as given. They preserve time of day data (if that is at all important to you).

Flattening an arbitrarily deep list (or any iterator) (Python)

2012-04-03T17:13:35-07:00

Python recipe 578092 by Garrett (flatten, iterator, itertools, list, python, tuple). Revision 6.

What if you had a list like this: [1, -10, [1,2,[3,4]], xrange(200)], and you just wanted to go through each element in order (wanted it to return a simple list of [1,-10,1,2,3,4,1,2,3,4...199])

I've seen a couple of attempts to flatten arbitrarily deep lists. Many of them involve recursion, like this one: http://rightfootin.blogspot.com/2006/09/more-on-python-flatten.html

Recursion is generally considered non-pythonic (at least to my knowledge), so I have used one which just involves simple iterators instead. Also, recursion will fail if the list is too deep (so it wouldn't really be arbitrary, would it?).

Using IviScope Instrument driver with Python (Python)

2012-03-29T17:17:26-07:00

Python recipe 578089 by Pierre Cladé .

This recipe shows how to use the IVI-COM interface of a scope. The example is based on a Tektronix scope using the tkdpo2k3k4k driver. Two examples are given : the first using the IviScope interface (limited interface to the scope, but with full compatibility) and the Tkdpo2k3k4k interface (specific to Tektronix).

For Characters in a String, Replace with Character (Python)

2012-03-23T20:44:23-07:00

Python recipe 578086 by Andrew Yurisich (character, replace, substitute, text). Revision 9.

Useful if you need to replace many different characters with all of the same character. Can accept an unlimited number of request to replace.

Does not work with words, only characters. You can, however, replace single characters with words. I may go back and re-implement it using tuples for the keys, but this would make searching the text for any matches pretty expensive, I'd imagine. At that point, it's mostly a job for a regex, and those tools already exist.

Lazy Dynamic Binding on Classes (You'll Never Go Back) (Python)

2011-08-12T23:42:27-07:00

Python recipe 577745 by Eric Snow (decorator, decorators, descriptor, descriptors). Revision 4.

This recipe provides a descriptor class and a decorator to make the deferred binding. Before the first access to that name, the __dict__ of the class will have the descriptor object. After that first access it will have whatever was returned by the first access.

One big advantage of deferring the binding is that the class object will be available at that time and can be passed to the object. During normal class creation the class body is exec'd before the class object is created, so the objects bound there can't be passed the class.

Recipe #577746 provides a concrete example of how the deferred_binder can be used.

Change a Function's Closure! (Python)

2011-08-12T23:25:55-07:00

Python recipe 577760 by Eric Snow (closure, function). Revision 2.

This is a hack to get around the read-only nature of __closure__ on function objects. Watch your step!

Logging asserts (Python)

2010-03-01T03:22:43-08:00

Python recipe 577074 by d.schlabing (logging). Revision 2.

This tries to marry assert statements with logging. If you use asserts together with logging and the script stops because an assertion is not fulfilled, you will not find any information about this in the logs. Unless you do something like this:

meal = ["eggs", "bacon", "spam"]
try:
    assert "spam" not in meal, "But I don't like spam!"
except AssertionError:
    log.exception("But I don't like spam!")
    raise

With the proposed recipe a somewhat similar behaviour can be achieved by:

log_assert("spam" not in meal, "But I don't like spam!")

Chaotic Function Analysis Graph (Python)

2010-12-10T03:31:50-08:00

Python recipe 577487 by FB36 (chaos, graph, graphics, math, mathematics). Revision 2.

There are 3 chaotic functions to graph as examples.

Graph of function (0) is a curve. Graph of function (1) is a group of lines. (Both are Xn+1 = f(Xn) type functions.)

Graph of function (2) on the other hand is a plane. (It is Xn+1 = f(Xn, Xn-1) type function.)

These mean there is a simple relationship between the previous and next X values in (0) and (1). (Next X value can always be predicted from the previous X value by using the graph of the function w/o knowing the function itself.) But (2) does not have a discernible relationship. (No prediction possible!) So (2) is clearly more chaotic than others. (I think it could be used as a Pseudo-Random Number Generator (PRNG).)

transform command line arguments to args and kwargs for a method call (Python)

2010-03-21T22:41:42-07:00

Python recipe 577122 by Trent Mick (argv, cli, json). Revision 2.

For many of my Python modules I find it convenient to provide a small if __name__ == "__main__": ... block to be able to call individual methods from the command line. This requires some kind of translation of command-line string arguments to args and kwargs for the method call. This recipe uses a few conventions to do that:

the first argument is the method name
positional args are positional (duh)
"key=value" is a keyword argument
an attempt is made to interpret arguments as JSON to allow specifying types other than string

simple state machine implementation (Python)

2010-07-15T17:54:17-07:00

Python recipe 577308 by David Klaffenbach (machine, state).

A very simple idiom for implementing a state machine.

dfs and bfs graph traversal (Python)

2013-06-28T09:59:38-07:00

Python recipe 576723 by bruce wernick (algorithm, graph).

Very simple depth first search and breath first graph traversal. This is based on the find_path written by Guido van Rossum.

RC4, ARC4, ARCFOUR algorithm (Python)

2009-05-03T09:45:59-07:00

Python recipe 576736 by Thimo Kraemer (algorithm, encryption, text). Revision 5.

RC4 generates a pseudorandom stream of bits (a keystream) which, for encryption, is combined with the plaintext using bit-wise exclusive-or; decryption is performed the same way (since exclusive-or is a symmetric operation).

(see http://en.wikipedia.org/wiki/RC4)