QNetworkAccessManager in PyQt
last modified July 9, 2020
QNetworkAccessManager in PyQt tutorial shows how to shows how to use QNetworkAccessManager
to send requests and receive responses.
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QNetworkAccessManager
QNetworkAccessManager
allows the application to send network requests and receive
replies. The QNetworkRequest
holds a request to be sent with the network
manager and the QNetworkReply
contains the data and headers returned for a
response.
QNetworkAccessManager
has an asynchronous API which means that its methods
always return immediately and do not wait until they finish. Instead, a signal
is emitted when the request is done. We handle the response in the method
attached to the finished signal.
HTTP GET request
The HTTP GET method requests a representation of the specified resource.
#!/usr/bin/python ''' QNetworkAccessManager in PyQt In this example we get a web page. Author: Jan Bodnar Website: zetcode.com ''' from PyQt5 import QtNetwork from PyQt5.QtCore import QCoreApplication, QUrl import sys class Example: def __init__(self): self.doRequest() def doRequest(self): url = 'http://webcode.me' req = QtNetwork.QNetworkRequest(QUrl(url)) self.nam = QtNetwork.QNetworkAccessManager() self.nam.finished.connect(self.handleResponse) self.nam.get(req) def handleResponse(self, reply): er = reply.error() if er == QtNetwork.QNetworkReply.NoError: bytes_string = reply.readAll() print(str(bytes_string, 'utf-8')) else: print("Error occured: ", er) print(reply.errorString()) QCoreApplication.quit() def main(): app = QCoreApplication([]) ex = Example() sys.exit(app.exec_()) if __name__ == '__main__': main()
The example retrieves the HTML code of the specified web page.
url = 'http://webcode.me' req = QtNetwork.QNetworkRequest(QUrl(url))
With the QNetworkRequest
we send a request to the specified URL.
self.nam = QtNetwork.QNetworkAccessManager() self.nam.finished.connect(self.handleResponse) self.nam.get(req)
A QNetworkAccessManager
object is created. When the request is
finished, the handleResponse
method is called. The request is fired with
the get
method.
def handleResponse(self, reply): er = reply.error() if er == QtNetwork.QNetworkReply.NoError: bytes_string = reply.readAll() print(str(bytes_string, 'utf-8')) else: print("Error occured: ", er) print(reply.errorString()) QCoreApplication.quit()
The handleResponse
receives a QNetworkReply
object.
It contains data and headers for the request that was sent. If there is no error
in the network reply, we read all data using the readAll
method;
otherwise we print an error message. The errorString
returns a
human-readable description of the last error that occurred. The
readAll
returns the data in QByteArray
that has to be
decoded.
$ ./get_request.py <!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>My html page</title> </head> <body> <p> Today is a beautiful day. We go swimming and fishing. </p> <p> Hello there. How are you? </p> </body> </html>
This is the output.
HTTP POST request
The HTTP POST method sends data to the server. The type of the body of the
request is indicated by the Content-Type
header. A POST request is
typically sent via an HTML form. The data sent in the request can be encoded in
different ways; in application/x-www-form-urlencoded
the values are
encoded in key-value tuples separated by '&', with a '=' between the key and
the value. Non-alphanumeric characters are percent encoded. The
multipart/form-data
is used for binary data and file uploads.
#!/usr/bin/python ''' QNetworkAccessManager in PyQt In this example we post data to a web page. Author: Jan Bodnar Website: zetcode.com ''' from PyQt5 import QtNetwork from PyQt5 import QtCore import sys, json class Example: def __init__(self): self.doRequest() def doRequest(self): data = QtCore.QByteArray() data.append('name=Peter&') data.append('age=34') url = 'https://httpbin.org/post' req = QtNetwork.QNetworkRequest(QtCore.QUrl(url)) req.setHeader(QtNetwork.QNetworkRequest.ContentTypeHeader, 'application/x-www-form-urlencoded') self.nam = QtNetwork.QNetworkAccessManager() self.nam.finished.connect(self.handleResponse) self.nam.post(req, data) def handleResponse(self, reply): er = reply.error() if er == QtNetwork.QNetworkReply.NoError: bytes_string = reply.readAll() json_ar = json.loads(str(bytes_string, 'utf-8')) data = json_ar['form'] print(f"Name: {data['name']}") print(f"Age: {data['age']}") print() else: print('Error occurred: ', er) print(reply.errorString()) QtCore.QCoreApplication.quit() def main(): app = QtCore.QCoreApplication([]) ex = Example() sys.exit(app.exec_()) if __name__ == '__main__': main()
The example sends a post request to the https://httpbin.org/post
testing site, which sends the data back in JSON format.
data = QtCore.QByteArray() data.append('name=Peter&') data.append('age=34')
As per specification, we encode the data sent in the QByteArray
.
url = 'https://httpbin.org/post' req = QtNetwork.QNetworkRequest(QtCore.QUrl(url)) req.setHeader(QtNetwork.QNetworkRequest.ContentTypeHeader, 'application/x-www-form-urlencoded')
We specify the application/x-www-form-urlencoded
encoding type.
bytes_string = reply.readAll() json_ar = json.loads(str(bytes_string, 'utf-8')) data = json_ar['form'] print(f"Name: {data['name']}") print(f"Age: {data['age']}") print()
In the handler method, we read the response data and decode it. With the
built-in json
module, we extract the posted data.
$ ./post_request.py Name: Peter Age: 34
This is the output.
QNetworkAccessManager authentication
The authenticationRequired
signal is emitted whenever
a final server requests authentication before it delivers the requested contents.
#!/usr/bin/python ''' QNetworkAccessManager in PyQt In this example, we show how to authenticate to a web page. Author: Jan Bodnar Website: zetcode.com ''' from PyQt5 import QtCore, QtGui, QtNetwork import sys, json class Example: def __init__(self): self.doRequest() def doRequest(self): self.auth = 0 url = 'https://httpbin.org/basic-auth/user7/passwd7' req = QtNetwork.QNetworkRequest(QtCore.QUrl(url)) self.nam = QtNetwork.QNetworkAccessManager() self.nam.authenticationRequired.connect(self.authenticate) self.nam.finished.connect(self.handleResponse) self.nam.get(req) def authenticate(self, reply, auth): print('Authenticating') self.auth += 1 if self.auth >= 3: reply.abort() auth.setUser('user7') auth.setPassword('passwd7') def handleResponse(self, reply): er = reply.error() if er == QtNetwork.QNetworkReply.NoError: bytes_string = reply.readAll() data = json.loads(str(bytes_string, 'utf-8')) print(f"Authenticated: {data['authenticated']}") print(f"User: {data['user']}") print() else: print('Error occurred: ', er) print(reply.errorString()) QtCore.QCoreApplication.quit() def main(): app = QtCore.QCoreApplication([]) ex = Example() sys.exit(app.exec_()) if __name__ == '__main__': main()
In the example se use the https://httpbin.org
website to show how authentication
is done with QNetworkAccessManager
.
self.nam.authenticationRequired.connect(self.authenticate)
We connect the authenticationRequired
signal to the authenticate
method.
def authenticate(self, reply, auth): print('Authenticating') ...
The third parameter of the authenticate
method is the QAuthenticator
,
which is used to pass the required authentication information.
self.auth += 1 if self.auth >= 3: reply.abort()
The QNetworkAccessManager
keeps emitting the authenticationRequired
signal if the authentication fails. We abort the process after three failed attempts.
auth.setUser('user7') auth.setPassword('passwd7')
We set the user and the password to the QAuthenticator
.
bytes_string = reply.readAll() data = json.loads(str(bytes_string, 'utf-8')) print(f"Authenticated: {data['authenticated']}") print(f"User: {data['user']}") print()
The https://httpbin.org
responds with JSON data, which contains the user
name and a boolean value indicating authentication success.
$ ./authentication.py Authenticating Authenticated: True User: user7
This is the output.
QNetworkAccessManager fetch favicon
A favicon is a small icon associated with a particular website. In the following example we are going to download a favicon from a website.
#!/usr/bin/python ''' QNetworkAccessManager in PyQt In this example we fetch a favicon from a website. Author: Jan Bodnar Website: zetcode.com ''' from PyQt5 import QtCore, QtGui, QtNetwork import sys class Example: def __init__(self): self.doRequest() def doRequest(self): url = 'http://webcode.me/favicon.ico' req = QtNetwork.QNetworkRequest(QtCore.QUrl(url)) self.nam = QtNetwork.QNetworkAccessManager() self.nam.finished.connect(self.handleResponse) self.nam.get(req) def handleResponse(self, reply): er = reply.error() if er == QtNetwork.QNetworkReply.NoError: data = reply.readAll() self.saveFile(data) else: print('Error occured: ', er) print(reply.errorString()) QtCore.QCoreApplication.quit() def saveFile(self, data): f = open('favicon.ico', 'wb') with f: f.write(data) def main(): app = QtCore.QCoreApplication([]) ex = Example() sys.exit(app.exec_()) if __name__ == '__main__': main()
The code example downloads a Google's favicon.
self.nam.get(req)
We download the icon with the get
method.
data = reply.readAll() self.saveFile(data)
In the handleResponse
method we read the data and save it to the file.
def saveFile(self, data): f = open('favicon.ico', 'wb') with f: f.write(data)
The image data is saved on the disk in the saveFile
method.
In this tutorial, we have worked with QNetworkAccessManager
.
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