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<!DOCTYPE html>
<html>
<head>
<title>My-Rendezvous-with-Python</title>
<meta charset="utf-8">
<style>
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}
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font-weight: 400;
margin-bottom: 0;
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float: left;
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</style>
</head>
<body>
<textarea id="source">
name: about-me
layout: false
# About Me
I...
- am **Syamala Umamaheswaran**
- work for **Volkswagen Digital:Lab Berlin** as a Software Engineer
- like a good discussion around **Test Driven Development**, **Pair Programming**, **Java vs Kotlin**, **Software architectures**, **OAuth2**, **Spring Framework** ...
- occasionally blog @ https://dev.to/shyamala_u
- am fairly active in twitter @shyamala_u
---
name: inverse
layout: true
class: center, middle, inverse
---
#My Rendezvous with Python
https://shyamz-22.github.io/py-rendezvous/
---
name: cycle
layout: false
.left-column[
## cycle
]
.right-column[
Return elements from the iterable until it is exhausted. Then repeat the sequence indefinitely.
```python
clocks = ['🕛', '🕑', '🕓', '🕕', '🕗', '🕘', '🕚']
`clock = cycle(clocks)`
msg = 'Loading... '
for i in range(10):
print('\r' + msg + next(clock), end='')
sleep(1)
```
Output:
```bash
Loading... 🕗
```
]
.footnote[https://docs.python.org/3/library/itertools.html#itertools.cycle]
???
how it is a great tool, when writing command line tools.
---
name: count
layout: false
.left-column[
## count
]
.right-column[
Counting the occurence of the given value in an iterable.
```python
colours = ['red', 'yellow', 'orange', 'red', 'white']
random_string = 'thisisarandomstring'
red_count = `colours.count('red')`
i_count = `random_string.count("i")`
print(f'red appears "{red_count}" times')
print(f'i appears "{i_count}" times')
```
Output:
```bash
red appears "2" times
i appears "3" times
```
Writing count on the list is more elegant than writing `Collections.frequency(colors, "red")` in Java.
]
.footnote[https://docs.python.org/3/library/itertools.html#itertools.cycle]
---
name: counter
layout: false
.left-column[
## Counter
]
.right-column[
While `count` is for specific value in the list.
If you want to know running counts of all values in an iterable,
```python
from collections import Counter
word = 'pneumonoultramicroscopicsilicovolcanoconiosis'
print('Word: ', word)
c = Counter(word)
print('counter: ', c)
print('top 5: ', c.most_common(5))
```
Output:
```bash
Word: pneumonoultramicroscopicsilicovolcanoconiosis
counter: Counter({'o': 9, 'i': 6, 'c': 6, 'n': 4, 's': 4,
'l': 3, 'p': 2, 'u': 2, 'm': 2, 'r': 2, 'a': 2, 'e': 1, 't': 1, 'v': 1})
top 5: [('o', 9), ('i', 6), ('c', 6), ('n', 4), ('s', 4)]
```
]
.footnote[https://docs.python.org/3/library/collections.html#counter-objects]
---
name: data-classes
layout: false
.left-column[
## Data Classes
]
.right-column[
DataClasses are simply containers of data. They are normal Python classes with
some boilerplate code implemented already.
- You can make data classes immutable.
- Type Hints are mandatory, even though they are not enforced in runtime.
### But repeat after me: Type Hints are good and we stick to them!!
]
???
- dunder - Double under
- (.__init__(), .__repr__(), and .__eq__() are implemented already).
- Emphasize on the immutability
---
.left-column[
## Data Classes
]
.right-column[
```python
from dataclasses import dataclass
@dataclass(init=True,
repr=True,
eq=True,
order=False,
frozen=True, # default is false
unsafe_hash=False)
class InventoryItem:
name: str
unit_price: float
quantity_on_hand: int = 0
```
```python
item_cola_a = InventoryItem(name='cola',
unit_price=20.0,
quantity_on_hand=10)
item_cola_b = InventoryItem(name='cola',
unit_price=20.0,
quantity_on_hand=10)
print('Item: ', item_cola_b)
print('Equal? ', item_cola_a == item_cola_b)
```
Output:
```bash
Item: InventoryItem(name='cola', unit_price=20.0, quantity_on_hand=10)
Equal? True
```
]
.footnote[https://docs.python.org/3/library/dataclasses.html#module-dataclasses]
???
- Talk about the importance of Type Hints and Named Parameters
For
Integrity - type hints,
Readability - named parameters.
Simplicity - less boiler plate code
---
name: decorators
.left-column[
## Decorators
]
.right-column[
Decorators wraps a funtion, Modifying the behavior
```python
from functools import wraps
from flask import Flask, request, Response
app = Flask(__name__)
def requires_authentication(f):
@wraps(f)
def decorated():
auth = request.headers.get('Authorization')
if not auth or auth != 'Bearer my-secret-api-key':
return Response('Not Authorized',
401,
{'WWW-Authenticate': 'Bearer realm="Bearer"'})
return f()
return decorated
@app.route('/')
@requires_authentication
def hello_world():
return 'Hello, World!'
if __name__ == '__main__':
app.run()
```
]
???
Functions are just like any other objects in Python. Decorators are Functions
that takes in a function as input parameter and returns another function.
Makes code readable, at the same time the implementation is explicit. I
like that I could do this that is not part of a framework.
---
.left-column[
## Decorators
]
.right-column[
Output:
```bash
> curl -H 'Authorization: Bearer my-secret-api-key' \
http://127.0.0.1:5000/
Hello, World!
```
```
> curl http://127.0.0.1:5000/
Not Authorized
```
]
.footnote[https://realpython.com/primer-on-python-decorators/]
---
name: graceful-shutdown
.left-column[
## Graceful Shutdown
### Why
]
.right-column[
When application receives a `SIGTERM`,
- Server should stop receiving new requests
- Finish processing the ongoing requests
- Release any resources
- Exit
]
???
The SIGTERM signal is a generic signal used to cause program termination.
Unlike SIGKILL, this signal can be blocked, handled, and ignored.
It is the normal way to politely ask a program to terminate.
---
.left-column[
## Graceful Shutdown
### Why
### Python
]
.right-column[
If you use [gunicorn](http://docs.gunicorn.org/en/stable/index.html) as a server,
it will handle the shutdown for you, by default it waits for 30 seconds before it kills an open connection.
You don’t have to handle the SIGTERM within your application.
```
> pipenv install gunicorn
> gunicorn "src:app() --graceful-timeout 10"
```
]
---
.left-column[
## Graceful Shutdown
### Why
### Python
### Go
]
.right-column[
```go
func main() {
mux := http.NewServeMux()
mux.HandleFunc("/", random)
server := http.Server{
Addr: ":8080",
Handler: mux,
}
go func() {
server.ListenAndServe()
}()
// here the magic happens
osSignals := make(chan os.Signal, 1)
// subscribe to SIGTERM
signal.Notify(osSignals, syscall.SIGTERM)
select {
case <-osSignals:
log.Print("caught signal, shutting down")
// create timeout
const timeout = 10 * time.Second
ctx, cancel := context.WithTimeout(context.Background(), timeout)
defer cancel()
// wait before dying, context will release resources
server.Shutdown(ctx)
}
}
```
]
---
.left-column[
## Graceful Shutdown
### Why
### Python
### Go
### Java + Tomcat + Spring
]
.right-column[
A small peek into graceful shutdown in Java + Tomcat + Spring Framework
```Java
@SpringBootApplication
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
@Bean
public GracefulShutdown gracefulShutdown() {
return new GracefulShutdown();
}
@Bean
public WebServerFactoryCustomizer tomcatCustomizer(GracefulShutdown gracefulShutdown) {
return factory -> {
if (factory instanceof TomcatServletWebServerFactory) {
((TomcatServletWebServerFactory) factory)
.addConnectorCustomizers(gracefulShutdown);
}
};
}
```
To Be Continued ...
]
---
.left-column[
## Graceful Shutdown
### Why
### Python
### Go
### Java + Tomcat + Spring
]
.right-column[
```Java
private static class GracefulShutdown implements
TomcatConnectorCustomizer,
ApplicationListener<ContextClosedEvent> {
private static final Logger log
= LoggerFactory.getLogger(GracefulShutdown.class);
private volatile Connector connector;
@Override
public void customize(Connector connector) {
this.connector = connector;
}
@Override
public void onApplicationEvent(ContextClosedEvent event) {
log.warn("received ContextClosedEvent");
Executor executor = this.connector.getProtocolHandler().getExecutor();
if (executor instanceof ThreadPoolExecutor) {
try {
ThreadPoolExecutor threadPoolExecutor = (ThreadPoolExecutor) executor;
threadPoolExecutor.shutdown();
if (!threadPoolExecutor.awaitTermination(10, TimeUnit.SECONDS)) {
log.warn("Tomcat thread pool did not shut down gracefully within "
+ "10 seconds. Proceeding with forceful shutdown");
}
}
catch (InterruptedException ex) {
Thread.currentThread().interrupt();
}
}
}
}
```
]
---
template: inverse
name: zen
# [The Zen of Python](https://www.python.org/dev/peps/pep-0020/#id3)
---
name: zen-values
class: middle
A collection of 19 "guiding principles" that influence the design of the Python programming language.
```python
> python3 -m this
The Zen of Python, by Tim Peters
`Beautiful is better than ugly.`
`Explicit is better than implicit.`
`Simple is better than complex.`
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
`Readability counts.``
Special cases aren't special enough to break the rules.
Although practicality beats purity.
`Errors should never pass silently.`
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
`If the implementation is hard to explain, it's a bad idea.`
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!
```
---
template: inverse
name: thank-you
#Thank you!
https://shyamz-22.github.io/py-rendezvous
Slides By [Remark](https://remarkjs.com)
</textarea>
<script src="https://remarkjs.com/downloads/remark-latest.min.js">
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<script>
var hljs = remark.highlighter.engine;
</script>
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var slideshow = remark.create({
highlightLanguage: 'python',
highlightStyle: 'dracula',
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</body>
</html>