python-cookbook | Code samples from the `` Python Cookbook | Learning library
kandi X-RAY | python-cookbook Summary
kandi X-RAY | python-cookbook Summary
Code samples from the "Python Cookbook, 3rd Edition", published by O’Reilly & Associates, May, 2013.
Support
Quality
Security
License
Reuse
Top functions reviewed by kandi - BETA
- Perform a daemonization process .
- Finds a module .
- Find a loader for a full name .
- Parses an namel list .
- Register a method .
- Parses an element and removes it from the given path .
- Acquires all of the specified locks .
- Used to print out the class that implements .
- Write polys .
- Get the next item .
python-cookbook Key Features
python-cookbook Examples and Code Snippets
Lines of Code : 57
License : No License
Copy
def decorator_apply(dec, func):
"""
Decorate a function by preserving the signature even if dec
is not a signature-preserving decorator.
"""
return FunctionMaker.create(
func, 'return decfunc(%(shortsignature)s)',
def decorator_apply(dec, func):
"""
Decorate a function by preserving the signature even if dec
is not a signature-preserving decorator.
"""
return FunctionMaker.create(
func, 'return decfunc(%(shortsignature)s)',
pip install futures
pip install python-parallel-collections
from parallel import parallel
>>> def double_iterables(l):
... for item in l:
... return map(double, l)
...
>>> parallel_gen = parallel([[1,2,3],[4,5,6]])
> Community Discussions
Trending Discussions on python-cookbook
QUESTION
I am trying to understand the design of dispatch table in function tables.
Here is what I initially coded
...ANSWER
Answered 2021-Oct-18 at 09:17To understand the issue, let's read the code as the interpreter does, line by line:
QUESTION
I'm trying to put together a utility that works kind of like Python's dataclass but gives me some additional things I can do like type checking on assignment, etc. I'm basically following the general pattern described in "9.21 Avoiding Repetitive Property Methods" from the O'Reilly Python Cookbook, 3rd Edition
I'm running into an issue where subsequent instantiations of MyClass overwrite data from other instances of it. Here's a simplified version of what I'm doing:
ANSWER
Answered 2021-May-20 at 10:12You're correct that the reference to the default value is shared between MyClass instances, and your tests confirm as much. One important piece of information to understand why this happens is that, other than e.g. the body of an __init__ function, a class-body only gets evaluated once; on class creation. There is no way for two or more different default-objects to exist, because the code related to it does not get executed when creating a new MyClass instance.
dataclasses solve this issue of having default values defined in the class body by having both default for immutable default values and default_factory for mutable default values. I'd suggest to just use a similar pattern for your construct, the alternative of creating copies is bound to create problems in case you actually do want to share an object between instances:
QUESTION
Consider the following minimized example:
Code:
...ANSWER
Answered 2021-Feb-26 at 18:15You can use a dict to map a letter to its correct position:
QUESTION
The following code snippet is from python cook book, 3rd Ed. Chapter 8.21:
...ANSWER
Answered 2021-Jan-03 at 16:50meth = self.generic_visit makes meth refer to the method self.generic_visit itself. It does not refer to its return value; that would be obtained by calling meth(x) for some x.
QUESTION
I am using TKinter to build a GUI (for a socket connection to a multichannel analyzer) to receive & plot data (~15.000.000 values) in regular intervals (~15 seconds).
While receiving data I don't want the GUI to freeze, so I am using multi-threading for connection handling, data receiving & plotting operations. I accomplished this, as seen in the reproducable code, with setting an event with threading.Event() and handle one thread after another (few lines of code in initSettings() & acquireAndPlotData). The only time I interfere with the GUI is when plotting to the canvas & I do this with tkinters after() method.
When started, the code runs without freezing & receives and plots as long as the window is opened & works as expected.
As I read on handling blocking I/O operations in tkinter GUIs, I only found examples with queuing and checking the queue recursively (with Queue & after(),
1
2
3
4
5
), but I found it to be way more convenient and easier to handle these operations with threading.Event().
Now my question is:
Am I using the right approach or am I missing something important here? (regarding thread safety, race conditions, what if plotting fails and takes longer than data acquisiton? Something I don't think of? Bad practices? etc...)
I would be really thankful for feedback on this matter!
Reproducable code
...ANSWER
Answered 2020-Aug-14 at 20:29So I did it like this but I do not know if it fits to you or if this is a good way to do this, but it safes you the .after as stated in the comments, which has the benefit that your function do_stuff is just called when needed.
QUESTION
I am trying to store a pickled nested dictionary in Postgresql (I am aware that this is a quick & dirty method and won't be able to access dictionary contents from Postgresql - usually bad practice)
...ANSWER
Answered 2020-Jul-18 at 18:12When your CREATE TABLE lists two fields, you have to list in INSERT which ones you want to fill, unless you fill them all.
QUESTION
I have functioning code that displays data in a GUI which is periodically updated with new information downloaded from the web. (The base code for the threaded approach was sourced from https://www.oreilly.com/library/view/python-cookbook/0596001673/ch09s07.html) I am using a threaded solution so as to improve blocking IO issues (IO code not included in the simplified code example below, as the IO does not appear to be the problem). The code runs fine if I run it as a single instance. However, it would be most convenient if I could use multiprocessing to run several instances of the code in parallel, using a different input list for each instance. When I try to implement the multiprocessing version, each separate process hangs during the attempt to create the root window: "window = tk.Tk()". Here is the working single instance version:
...ANSWER
Answered 2020-Jun-28 at 19:07You cannot use tkinter code across multiple processes. At least, you can't run the same tkinter code. It simply isn't designed to be used that way. When you create a root window, underneath the covers a tcl interpreter is created, and this interpreter can't be pickled or shared between processes, and doesn't use python's global interpreter lock.
In short, all of your GUI code needs to be in a single thread in a single process.
The following answer is a slightly better explanation, written by one of the developers on the Tcl core team: https://stackoverflow.com/a/38767665/7432. Here is the opening paragraph of that answer:
Each Tcl interpreter object (i.e., the context that knows how to run a Tcl procedure) can only be safely used from the OS thread that creates it. This is because Tcl doesn't use a global interpreter lock like Python, and instead makes extensive use of thread-specific data to reduce the number of locks required internally. (Well-written Tcl code can take advantage of this to scale up very large on suitable hardware.)
QUESTION
In the last couple of weeks, I've been trying to make an application that can read EEG data from OpenBCI Cyton (@250Hz) and plot a graph in 'real-time'. What seems to work better here are threads. I applied the tips I found here 1 to communicate the thread with Tkinter, but the application still doesn't work (gives me the error RecursionError: maximum recursion depth exceeded while calling a Python object). Maybe I'm doing something wrong because I'm trying to use multiple .py files? See below the main parts of my code and a few more comments in context:
ANSWER
Answered 2020-Jun-09 at 02:41after() (similar to button's command= and bind()) needs function's name without () and without argument - it is called callback - and after sends it to mainloop and mainloop later uses () to run it.
You use function with ()
QUESTION
So my project is about showing information from a database in conjunction with images. The idea is the following:
I have a database that describes images. One table has general information, like which color is contained in which image and another table has more granular information, like where that color can be found, etc.
When I launch a search, I want two windows to open (ClassTwo and ClassThree).
Instead of the first Window that only contains a Button to launch the search, my full application contains fields that are used to filter a database request. When I launch that search I want e.g. all images with the color green in them, so ClassTwo would list all images with that color, along with additional metadata.
ClassThree would then list all areas that contain the same color, but with a bit more detail, like position in the image and size, etc.
Upon clicking on either of the MultiListbox, I want to open an ImageViewer that shows the image.
In case of ClassThree, I would also directly highlight the area that I clicked on, so both classes would have functions bound to the MultiListbox.
My problem is with the binding of the Listboxes, that does not work properly. When I use e.g. image_parts_info_lb.bind() the function is not triggered at all. When i use image_parts_info_lb.bind_all() only the function of the last MultiListbox is triggered.
You can find the original Python2 version of the MultiListbox in the comment of the class.
Here is my code
...ANSWER
Answered 2020-Jan-14 at 15:23Question:
MultiListboxcustom event binding problem, click on any of the list elements, trigger theprint_stuff_x function
Implement a custom event '<>' which get fired on processed a '<>' event and .bind(... at it.
Reference:
- Tkinter.Widget.event_generate-method
- event generate
Generates a window event and arranges for it to be processed just as if it had come from the window system. If the
-whenoption is specified then it determines when the event is processed.
Crore Point:
QUESTION
I'm trying to use python to turn on some RGB lights after motion is detected. My code is below but I can't get the thread to end and switch off the LEDS. All that happening is I get stuck after keyboard interrupt.
Essentially when I run the code it works to detect movement and switch the lights on but then when I try to end the program with a keyboard interupt exception either the program hangs and doesn't stop or it stops but the LEDs don't switch off and stay lit. I've looked at various pages about how to stop a thread running but none of it has helped. Below are the articles I've looked at. I think my issue is that the thread running the lighting pattern loop isn't stopping so when I try to turn each LED off its turned back on immediately but I'm not sure.
I can't get the thread to stop any way I've tried. Any help would be much appreciated.
...ANSWER
Answered 2020-Jan-03 at 17:43Reduced to a minimal example so it can run without hardware. Comments added for fixes. The main problem was stop was only checked after 256*iterations*wait_ms/1000.0 or 25.6 seconds, so stopping appeared unresponsive. A few other bugs as well. Global stop is sufficient to end the thread so the Event wasn't needed.
Community Discussions, Code Snippets contain sources that include Stack Exchange Network
Vulnerabilities
No vulnerabilities reported
Install python-cookbook
You can use python-cookbook like any standard Python library. You will need to make sure that you have a development environment consisting of a Python distribution including header files, a compiler, pip, and git installed. Make sure that your pip, setuptools, and wheel are up to date. When using pip it is generally recommended to install packages in a virtual environment to avoid changes to the system.
Support
Reuse Trending Solutions
Find, review, and download reusable Libraries, Code Snippets, Cloud APIs from over 650 million Knowledge Items
Find more librariesStay Updated
Subscribe to our newsletter for trending solutions and developer bootcamps
Share this Page
