Pyqt Signals And Slots Across Threads
This interesting article evaluates how often are objects copied when passed across signal/slot connections in Qt. Basically, the outcome is that when passed by const reference in C++, objects are either not copied at all (for direct connections) or copied once (for queued connections).
How about PyQt? Does the same hold? For Python objects, when a copy is made, is it a deep copy?
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- A python program using an example cpp thread (TestThread) which communicates with PyQt signals and slots can be found here: valkkaexamples / apilevel2 / qt / cppthreaddemo. Py See also the documentation for the cpp source code of TestThread.
- Qt provides the signals and slots framework which allows you to do just that and is thread-safe, allowing safe communication directly from running threads to your GUI frontend. Signals allow you to.emit values, which are then picked up elsewhere in your code by slot functions which have been linked with.connect.
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I am interested primarily in PyQt5 and Python 3.
As suggested by @ekhumoro, I did try, and surprisingly I get a different result to what the test conducted in C++ reveals. Basically, my test shows that: objects are not copied at all, even when passed across thread boundaries using QueuedConnection
Consider the following test code:
The result is:
which shows that despite the emitting slot and the receiving slot living in different threads, they do share the data object sent over a QueuedConnection.
How to check for multiple attributes in a list
python,python-2.7
You can create a set holding the different IDs and then compare the size of that set to the total number of quests. The difference tells you how many IDs are duplicated. Same for names. Something like this (untested): def test_quests(quests): num_total = len(quests) different_ids = len(set((q.ID for q in...
Can't get value from xpath python
python,html,xpath,web-scraping,html-parsing
The values in the table are generated with the help of javascript being executed in the browser. One option to approach it is to automate a browser via selenium, e.g. a headless PhantomJS: >>> from selenium import webdriver >>> >>> driver = webdriver.PhantomJS() >>> driver.get('http://www.tabele-kalorii.pl/kalorie,Actimel-cytryna-miod-Danone.html') >>> >>> table = driver.find_element_by_xpath(u'//table[tbody/tr/td/h3...
ctypes error AttributeError symbol not found, OS X 10.7.5
python,c++,ctypes
Your first problem is C++ name mangling. If you run nm on your .so file you will get something like this: nm test.so 0000000000000f40 T __Z3funv U _printf U dyld_stub_binder If you mark it as C style when compiled with C++: #ifdef __cplusplus extern 'C' char fun() #else char fun(void)...
In sklearn, does a fitted pipeline reapply every transform?
python,scikit-learn,pipeline,feature-selection
The pipeline calls transform on the preprocessing and feature selection steps if you call pl.predict. That means that the features selected in training will be selected from the test data (the only thing that makes sense here). It is unclear what you mean by 'apply' here. Nothing new will be...
Identify that a string could be a datetime object
python,regex,algorithm,python-2.7,datetime
What about fuzzyparsers: Sample inputs: jan 12, 2003 jan 5 2004-3-5 +34 -- 34 days in the future (relative to todays date) -4 -- 4 days in the past (relative to todays date) Example usage: >>> from fuzzyparsers import parse_date >>> parse_date('jun 17 2010') # my youngest son's birthday datetime.date(2010,...
trying to understand LSH through the sample python code
python,similarity,locality-sensitive-hash
a. It's a left shift: https://docs.python.org/2/reference/expressions.html#shifting-operations It shifts the bits one to the left. b. Note that ^ is not the 'to the power of' but 'bitwise XOR' in Python. c. As the comment states: it defines 'number of bits per signature' as 2**10 → 1024 d. The lines calculate...
Displaying a 32-bit image with NaN values (ImageJ)
python,image-processing,imagej
The display range of your image might not be set correctly. Try outputImp.resetDisplayRange() or outputImp.setDisplayRange(Stats.min, Stats.max) See the ImagePlus javadoc for more info....
Sort when values are None or empty strings python
python,list,sorting,null
If you want the None and ' values to appear last, you can have your key function return a tuple, so the list is sorted by the natural order of that tuple. The tuple has the form (is_none, is_empty, value); this way, the tuple for a None value will be...
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python,module,python-module
The convention is to declare constants in modules as variables written in upper-case (Python style guide: https://www.python.org/dev/peps/pep-0008/#global-variable-names). But there's no way to prevent someone else to re-declare such a variable -- thus ignoring conventions -- when importing a module. There are two ways of working around this when importing modules...
SQLAlchemy. 2 different relationships for 1 column
python,sqlalchemy
I'm afraid you can't do it like this. I suggest you have just one relationship users and validate the insert queries.
sys.argv in a windows environment
python,windows,python-3.x
You are calling the script wrong Bring up a cmd (command line prompt) and type: cd C:/Users/user/PycharmProjects/helloWorld/ module_using_sys.py we are arguments And you will get the correct output....
Inserting a variable in MongoDB specifying _id field
python,mongodb,pymongo
Insert only accepts a final document or an array of documents, and an optional object which contains additional options for the collection. db.collection.insert( <document or array of documents>, { // options writeConcern: <document>, ordered: <boolean> } ) You may want to add the _id to the document in advance, but...
Django: html without CSS and the right text
python,html,css,django,url
Are you using the {% load staticfiles %} in your templates?
Replace nodejs for python?
python,node.js,webserver
You might want to have a look at Tornado. It is well-documented and features built-in support for WebSockets. If you want to steer clear of the Tornado-framework, there are several Python implementations of Socket.io. Good luck!...
SyntaxError: invalid syntax?
python,syntax
Check the code before the print line for errors. This can be caused by an error in a previous line; for example: def x(): y = [ print 'hello' x() This produces the following error: File 'E:Pythontest.py', line 14 print 'hello' ^ SyntaxError: invalid syntax When clearly the error is...
How to change the IP address of Amazon EC2 instance using boto library
python,amazon-web-services,boto
Make sure you have set properly with ~/.boto and connect to aws, have the boto module ready in python. If not, go through this first: Getting Started with Boto For example, you need assign a new EIP 54.12.23.34 to the instance i-12345678 Make sure, EIP has been allocated(existed) and you...
Peewee: reducing where conditionals break after a certain length
python,peewee
Try ...where(SomeTable.BIN.in_(big_list)) PeeWee has restrictions as to what can be used in their where clause in order to work with the library. http://docs.peewee-orm.com/en/latest/peewee/querying.html#query-operators...
Python: histogram/ binning data from 2 arrays.
python,histogram,large-files
if you only need to do this for a handful of points, you could do something like this. If intensites and radius are numpy arrays of your data: bin_width = 0.1 # Depending on how narrow you want your bins def get_avg(rad): average_intensity = intensities[(radius>=rad-bin_width/2.) & (radius<rad+bin_width/2.)].mean() return average_intensities #...
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python,list
Your list contains one dictionary you can access the data inside like this : >>> yourlist[0]['popularity'] 2354 [0] for the first item in the list (the dictionary). ['popularity'] to get the value associated to the key 'popularity' in the dictionary....
Spring-integration scripting with Python
python,spring-integration,jython
This is a bug in Spring Integration; I have opened a JIRA Issue. if (variables != null) { result = scriptEngine.eval(script, new SimpleBindings(variables)); } else { result = scriptEngine.eval(script); } When the first branch of the if test is taken, the result variable is added to the SimpleBindings object, and...
Using counter on array for one value while keeping index of other values
python,collections
To count how often one value occurs and at the same time you want to select those values, you'd simply select those values and count how many you selected: fruits = [f for f in foods if f[0] 'fruit'] fruit_count = len(fruits) If you need to do this for...
how to enable a entry by clicking a button in Tkinter?
python,tkinter
You need to use the configure method of each widget: def rakhi(): entry1.configure(state='normal') entry2.configure(state='normal') ...
odoo v8 - Field(s) `arch` failed against a constraint: Invalid view definition
python,xml,view,odoo,add-on
You have made silly mistake in defining _columns. _colums is not valid dictionary name for fields structure. Replace this by _columns and restart service and update module. ...
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python,html,django,templates,django-1.4
You can use the include tag in order to supply the included template with a consistent variable name: For example: parent.html <div> <div> {% include 'templates/child.html' with list_item=mylist.0 t=50 only %} </div> </div> child.html {{ list_item.text truncatewords:t }} UPDATE: As spectras recommended, you can use the...
Python: can't access newly defined environment variables
python,bash,environment-variables
After updating your .bashrc, perform source ~/.bashrc to apply the changes. Also, merge the two BONSAI-related calls into one: export BONSAI=/home/me/Utils/bonsai_v3.2 UPDATE: It was actually an attempt to update the environment for some Eclipse-based IDE. This is a different usecase altogether. It should be described in the Eclipse help. Also,...
Pandas - Dropping multiple empty columns
python,pandas
You can just subscript the columns: df = df[df.columns[:11]] This will return just the first 11 columns or you can do: df.drop(df.columns[11:], axis=1) To drop all the columns after the 11th one....
How to remove structure with python from this case?python,python-2.7
It's complicated to use regex, a stupid way I suggested: def remove_table(s): left_index = s.find('<table>') if -1 left_index: return s right_index = s.find('</table>', left_index) return s[:left_index] + remove_table(s[right_index + 8:]) There may be some blank lines inside the result....
Python recursive function not recursing
python,recursion
Afraid I don't know much about python, but I can probably help you with the algorithm. The encoding process repeats the following: multiply the current total by 17 add a value (a = 1, b = 2, ..., z = 26) for the next letter to the total So at...
Twilio Client Python not Working in IOS Browser
javascript,python,ios,flask,twilio
Twilio developer evangelist here. Twilio Client uses WebRTC and falls back to Flash in order to make web browsers into phones. Unfortunately Safari on iOS supports neither WebRTC nor Flash so Twilio Client cannot work within any browser on iOS. It is possible to build an iOS application to use...
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python,numpy,kernel-density
As stated in my comment, this is an issue with kernel density support. The Gaussian kernel has infinite support. Even fit on data with a specific range the range of the Gaussian kernel will be from negative to positive infinity. That being said the large majority of the density will...
Parse text from a .txt file using csv module
python,python-2.7,parsing,csv
How about using Regular Expression def get_info(string_to_search): res_dict = {} import re find_type = re.compile('Type:[s]*[w]*') res = find_type.search(string_to_search) res_dict['Type'] = res.group(0).split(':')[1].strip() find_Status = re.compile('Status:[s]*[w]*') res = find_Status.search(string_to_search) res_dict['Status'] = res.group(0).split(':')[1].strip() find_date = re.compile('Date:[s]*[/0-9]*') res = find_date.search(string_to_search) res_dict['Date'] = res.group(0).split(':')[1].strip() res_dict['description'] =...
Find the tf-idf score of specific words in documents using sklearn
python,scikit-learn,tf-idf
Yes. See .vocabulary_ on your fitted/transformed TF-IDF vectorizer. In [1]: from sklearn.datasets import fetch_20newsgroups In [2]: data = fetch_20newsgroups(categories=['rec.autos']) In [3]: from sklearn.feature_extraction.text import TfidfVectorizer In [4]: cv = TfidfVectorizer() In [5]: X = cv.fit_transform(data.data) In [6]: cv.vocabulary_ It is a dictionary of the form: {word : column index in...
represent an index inside a list as x,y in python
python,list,numpy,multidimensional-array
According to documentation of numpy.reshape , it returns a new array object with the new shape specified by the parameters (given that, with the new shape, the amount of elements in the array remain unchanged) , without changing the shape of the original object, so when you are calling the...
Count function counting only last line of my list
python,python-2.7
I don't know what you are exactly trying to achieve but if you are trying to count R and K in the string there are more elegant ways to achieve it. But for your reference I had modified your code. N = int(raw_input()) s = [] for i in range(N):...
REGEX python find previous string
python,regex,string
Updated: This will check for the existence of a sentence followed by special characters. It returns false if there are no special characters, and your original sentence is in capture group 1. Updated Regex101 Example r'(.*[w])([^w]+)' Alternatively (without a second capture group): Regex101 Example - no second capture group r'(.*[w])(?:[^w]+)'...
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python,python-2.7,behavior
Short answer: your correct doesn't work. Long answer: The binary floating-point formats in ubiquitous use in modern computers and programming languages cannot represent most numbers like 0.1, just like no terminating decimal representation can represent 1/3. Instead, when you write 0.1 in your source code, Python automatically translates this to...
Python np.delete issue
python,numpy
Don't call np.delete in a loop. It would be quicker to use boolean indexing: In [6]: A[X.astype(bool).any(axis=0)] Out[6]: array([[3, 4, 5]]) X.astype(bool) turns 0 into False and any non-zero value into True: In [9]: X.astype(bool).any(axis=0) Out[9]: array([False, True, False], dtype=bool) the call to .any(axis=0) returns True if any value in...
How to put an image on another image in python, using ImageTk?
python,user-interface,tkinter
Just use photoshop or G.I.M.P.. I assure you, doing it that way will be much simpler and less redundant than essentially getting Tkinter to photo edit for you (not to mention what you're talking about is just bad practice when it comes to coding) Anyways, I guess if you really...
Calling function and passing arguments multiple times
python,function,loops
a,b,c = 1,2,3 while i<n: a,b,c = myfunction(a,b,c) i +=1 ...
Sum of two variables in RobotFramework
python,automated-tests,robotframework
By default variables are string in Robot. So your first two statements are assigning strings like 'xx,yy' to your vars. Then 'evaluate' just execute your statement as Python would do. So, adding your two strings with commas will produce a list: $ python >>> 1,2+3,4 (1, 5, 4) So you...
Python - Opening and changing large text files
python,replace,out-of-memory,large-files
You need to read one bite per iteration, analyze it and then write to another file or to sys.stdout. Try this code: mesh = open('file.mesh', 'r') mesh_out = open('file-1.mesh', 'w') c = mesh.read(1) if c: mesh_out.write('{') else: exit(0) while True: c = mesh.read(1) if c ': break if c...
Matplotlib: Plot the result of an SQL query
python,sql,matplotlib,plot
Take this for a starter code : import numpy as np import matplotlib.pyplot as plt from sqlalchemy import create_engine import _mssql fig = plt.figure() ax = fig.add_subplot(111) engine = create_engine('mssql+pymssql://**:****@127.0.0.1:1433/AffectV_Test') connection = engine.connect() result = connection.execute('SELECT Campaign_id, SUM(Count) AS Total_Count FROM Impressions GROUP BY Campaign_id') ## the data data =...
Create an exe with Python 3.4 using cx_Freeze
python,python-3.4,cx-freeze
Since you want to convert python script to exe have a look at py2exe
group indices of list in list of lists
python,list
Use collections.OrderedDict: from collections import OrderedDict od = OrderedDict() lst = [2, 0, 1, 1, 3, 2, 1, 2] for i, x in enumerate(lst): od.setdefault(x, []).append(i) ... >>> od.values() [[0, 5, 7], [1], [2, 3, 6], [4]] ...
The event loop is already running
python,python-3.x,pyqt,pyqt4
I think the problem is with your start.py file. You have a function refreshgui which re imports start.py import will run every part of the code in the file. It is customary to wrap the main functionality in an 'if __name__ '__main__': to prevent code from being run on...
MySQLdb Python - Still getting error when using CREATE TABLE IF NOT EXISTS
python,mysql
MySQL is actually throwing a warning rather that an error. You can suppress mysql warnings like this : import MySQLdb as mdb from warnings import filterwarnings filterwarnings('ignore', category = mdb.Warning) Now the mysql warnings will be gone. But mysql errors will be shown as usual Read more about warnings at...
Pandas Dataframe Complex Calculation
python,python-2.7,pandas,dataframes
I believe the following does what you want: In [24]: df['New_Col'] = df['ActualCitations']/pd.rolling_sum(df['totalPubs'].shift(), window=2) df Out[24]: Year totalPubs ActualCitations New_Col 0 1994 71 191.002034 NaN 1 1995 77 2763.911781 NaN 2 1996 69 2022.374474 13.664692 3 1997 78 3393.094951 23.240376 So the above uses rolling_sum and shift to generate the...
Python Popen - wait vs communicate vs CalledProcessError
python,python-2.7,error-handling,popen
about the deadlock: It is safe to use stdout=PIPE and wait() together iff you read from the pipe. .communicate() does the reading and calls wait() for you about the memory: if the output can be unlimited then you should not use .communicate() that accumulates all output in memory. what...
How does the class_weight parameter in scikit-learn work?
python,scikit-learn
First off, it might not be good to just go by recall alone. You can simply achieve a recall of 100% by classifying everything as the positive class. I usually suggest using AUC for selecting parameters, and then finding a threshold for the operating point (say a given precision level)...
Introduction
In some applications it is often necessary to perform long-running tasks, such as computations or network operations, that cannot be broken up into smaller pieces and processed alongside normal application events. In such cases, we would like to be able to perform these tasks in a way that does not interfere with the normal running of the application, and ensure that the user interface continues to be updated. One way of achieving this is to perform these tasks in a separate thread to the main user interface thread, and only interact with it when we have results we need to display.
This example shows how to create a separate thread to perform a task - in this case, drawing stars for a picture - while continuing to run the main user interface thread. The worker thread draws each star onto its own individual image, and it passes each image back to the example's window which resides in the main application thread.
The User Interface
We begin by importing the modules we require. We need the math and random modules to help us draw stars.
The main window in this example is just a QWidget. We create a single Worker instance that we can reuse as required.
The user interface consists of a label, spin box and a push button that the user interacts with to configure the number of stars that the thread wil draw. The output from the thread is presented in a QLabel instance, viewer.
We connect the standard finished() and terminated() signals from the thread to the same slot in the widget. This will reset the user interface when the thread stops running. The custom output(QRect, QImage) signal is connected to the addImage() slot so that we can update the viewer label every time a new star is drawn.
The start button's clicked() signal is connected to the makePicture() slot, which is responsible for starting the worker thread.
We place each of the widgets into a grid layout and set the window's title:
The makePicture() slot needs to do three things: disable the user interface widgets that are used to start a thread, clear the viewer label with a new pixmap, and start the thread with the appropriate parameters.
Since the start button is the only widget that can cause this slot to be invoked, we simply disable it before starting the thread, avoiding problems with re-entrancy.
We call a custom method in the Worker thread instance with the size of the viewer label and the number of stars, obtained from the spin box.
Whenever is star is drawn by the worker thread, it will emit a signal that is connected to the addImage() slot. This slot is called with a QRect value, indicating where the star should be placed in the pixmap held by the viewer label, and an image of the star itself:
Pyqt Signals And Slots Across Threads Crossword
We use a QPainter to draw the image at the appropriate place on the label's pixmap.
The updateUi() slot is called when a thread stops running. Since we usually want to let the user run the thread again, we reset the user interface to enable the start button to be pressed:
Now that we have seen how an instance of the Window class uses the worker thread, let us take a look at the thread's implementation.
The Worker Thread
The worker thread is implemented as a PyQt thread rather than a Python thread since we want to take advantage of the signals and slots mechanism to communicate with the main application.
We define size and stars attributes that store information about the work the thread is required to do, and we assign default values to them. The exiting attribute is used to tell the thread to stop processing.
Each star is drawn using a QPainterPath that we define in advance:
Before a Worker object is destroyed, we need to ensure that it stops processing. For this reason, we implement the following method in a way that indicates to the part of the object that performs the processing that it must stop, and waits until it does so.
For convenience, we define a method to set up the attributes required by the thread before starting it.
The start() method is a special method that sets up the thread and calls our implementation of the run() method. We provide the render() method instead of letting our own run() method take extra arguments because the run() method is called by PyQt itself with no arguments.
The run() method is where we perform the processing that occurs in the thread provided by the Worker instance:
Information stored as attributes in the instance determines the number of stars to be drawn and the area over which they will be distributed.
We draw the number of stars requested as long as the exiting attribute remains False. This additional check allows us to terminate the thread on demand by setting the exiting attribute to True at any time.
The drawing code is not particularly relevant to this example. We simply draw on an appropriately-sized transparent image.
For each star drawn, we send the main thread information about where it should be placed along with the star's image by emitting our custom output() signal:
Since QRect and QImage objects can be serialized for transmission via the signals and slots mechanism, they can be sent between threads in this way, making it convenient to use threads in a wide range of situations where built-in types are used.
Running the Example
Pyqt Signals And Slots Across Threads Free
We only need one more piece of code to complete the example: