Comet or Server Push is a technique for enabling real-time updates between the server and the client. In Google App Engine (GAE), you can implement Server Push using techniques like long polling or WebSockets. In this example, we'll demonstrate how to implement Comet using long polling in Python on GAE.
Create a Google App Engine project: If you haven't already, set up a Google App Engine project. You'll need a project ID, the Google Cloud SDK installed, and your application configured.
Create a GAE application:
Create a new folder for your GAE application and set up the necessary files, including app.yaml, requirements.txt, and a Python script for your application.
Install the necessary libraries:
You'll need the webapp2 library to create a web application in GAE. You can include it in your requirements.txt file:
webapp2
Then, run pip install -r requirements.txt to install the dependencies.
Create a Python script:
Create a Python script (e.g., main.py) for your GAE application. In this script, you'll implement the Comet (long polling) functionality.
import webapp2
import time
class CometHandler(webapp2.RequestHandler):
def get(self):
# Implement your long-polling logic here
# For example, you can wait for updates or events and then respond to the client
# For demonstration, we will simply wait for 5 seconds and then send a response
time.sleep(5)
self.response.write('This is a response from the server after 5 seconds.')
app = webapp2.WSGIApplication([
('/comet', CometHandler),
], debug=True)
Configure app.yaml:
Configure your app.yaml file to define the URL mapping for your application:
runtime: python27 api_version: 1 threadsafe: true handlers: - url: /comet script: main.app
Deploy your GAE application: Deploy your GAE application using the Google Cloud SDK:
gcloud app deploy
Access the Comet endpoint:
Once your application is deployed, you can access the Comet endpoint at /comet. This endpoint will simulate a long-polling request, and after a delay of 5 seconds (as specified in the example), it will send a response to the client.
Remember that this is a simplified example to demonstrate the concept of Comet with long polling in Google App Engine. In a real-world application, you would typically implement more complex logic to handle real-time updates and events between the server and clients. Additionally, consider using more advanced techniques like WebSockets for more efficient real-time communication when building production-ready applications.
In Google App Engine (GAE) datastore, if you want to copy an entity without knowing the property names at "compile" time, you can use Python's built-in getattr and setattr functions to dynamically access and set properties. Here's how you can achieve this:
Let's say you have an entity SourceEntity that you want to copy:
from google.cloud import datastore
datastore_client = datastore.Client()
class SourceEntity(datastore.Entity):
# Define properties (can be dynamic)
pass
And you want to copy this entity to create a new TargetEntity:
class TargetEntity(datastore.Entity):
# Define properties (can be dynamic)
pass
# Function to copy an entity
def copy_entity(source_entity):
target_entity = TargetEntity()
# Iterate through properties of source_entity
for name, value in source_entity.items():
# Set the same property on the target_entity
setattr(target_entity, name, value)
return target_entity
# Example usage:
source_entity = SourceEntity()
source_entity["property1"] = "value1"
source_entity["property2"] = "value2"
# Copy the entity
target_entity = copy_entity(source_entity)
# Save the target_entity to the datastore
datastore_client.put(target_entity)
In this example:
We define SourceEntity and TargetEntity classes, which can have dynamic properties. You can add or remove properties as needed.
The copy_entity function copies the properties from the source entity to the target entity using a loop. It uses setattr to dynamically set properties on the target entity based on the property names of the source entity.
You can create a source entity with dynamic properties, copy it to a target entity, and then save the target entity to the datastore.
This approach allows you to copy entities without knowing the property names at "compile" time. However, keep in mind that you should handle data type conversions and other aspects of your specific entity schema as needed.
Packing and unpacking in Python usually refer to two different concepts: packing refers to collecting multiple values into a single data structure, like a tuple or a list, while unpacking refers to extracting values from a data structure. Let's go through both concepts with examples.
Packing involves combining multiple values into a single data structure like a tuple or a list.
# Packing into a tuple packed_tuple = 1, 2, 3 print(packed_tuple) # Output: (1, 2, 3) # Packing into a list packed_list = [4, 5, 6] print(packed_list) # Output: [4, 5, 6]
Unpacking involves extracting values from a data structure like a tuple or a list.
# Unpacking a tuple a, b, c = packed_tuple print(a, b, c) # Output: 1 2 3 # Unpacking a list x, y, z = packed_list print(x, y, z) # Output: 4 5 6
You can also implement packing and unpacking in your custom objects by defining special methods like __getitem__, __setitem__, and __iter__. Here's an example:
class MyObject:
def __init__(self, *args):
self.data = list(args)
def __getitem__(self, index):
return self.data[index]
def __setitem__(self, index, value):
self.data[index] = value
def __iter__(self):
return iter(self.data)
# Packing values into MyObject
obj = MyObject(1, 2, 3)
# Unpacking values from MyObject
a, b, c = obj
print(a, b, c) # Output: 1 2 3
# Modifying values using unpacking
a, b, c = obj
a += 10
b += 20
c += 30
print(obj[0], obj[1], obj[2]) # Output: 11 22 33
In this example, the MyObject class demonstrates custom packing and unpacking behavior using special methods.
Remember that Python's built-in objects like tuples and lists are highly optimized for these operations, and you should consider using them unless you have specific reasons to implement custom packing and unpacking behaviors in your objects.
To send an HTML email in Google App Engine using Python, you can use the built-in smtplib library along with the email library. Here's a step-by-step guide to send an HTML email:
import smtplib from email.mime.multipart import MIMEMultipart from email.mime.text import MIMEText
"smtp.example.com" with your SMTP server, "[email protected]" with your email address, and "your_password" with your email password. Note that you might need to use an App Password or an API key for security reasons if you're using Gmail.smtp_server = "smtp.example.com" smtp_port = 587 smtp_username = "[email protected]" smtp_password = "your_password"
MIMEMultipart object and set the email subject, sender, and recipient(s):message = MIMEMultipart() message["Subject"] = "HTML Email Example" message["From"] = smtp_username message["To"] = "[email protected]"
MIMEText and set the content type to "html":html_content = """
<html>
<body>
<h1>Hello, World!</h1>
<p>This is an HTML email sent from Google App Engine.</p>
</body>
</html>
"""
html_part = MIMEText(html_content, "html")
message.attach(html_part)
try:
with smtplib.SMTP(smtp_server, smtp_port) as server:
server.starttls()
server.login(smtp_username, smtp_password)
server.sendmail(smtp_username, "[email protected]", message.as_string())
print("Email sent successfully")
except Exception as e:
print("Error:", str(e))
Make sure to enable access to less secure apps in your email account settings if you're using a Gmail account. Additionally, consider using an email library like secure-smtplib for added security.
Remember to replace the placeholders with your actual SMTP server, email credentials, and recipient's email address.
You can use the os module in Python to list the files in a directory and then sort them in ascending order. Here's an example:
import os
directory = '/path/to/your/directory'
# Get a list of filenames in the directory
filenames = os.listdir(directory)
# Sort the filenames in ascending order
sorted_filenames = sorted(filenames)
# Print the sorted filenames
for filename in sorted_filenames:
print(filename)
Replace '/path/to/your/directory' with the actual path to the directory you want to sort.
This code will list the filenames in the directory and then sort them in ascending order. You can modify the sorting behavior by providing additional arguments to the sorted() function. For example, if you want to sort the filenames in a case-insensitive manner:
sorted_filenames = sorted(filenames, key=lambda x: x.lower())
This will sort the filenames while ignoring the case of the letters.
Remember to adapt the code to your specific use case and directory structure.