Add python decorator answer

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surister 2019-12-02 10:36:18 +01:00
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<details> <details>
<summary>Explain what is a decorator</summary><br><b> <summary>Explain what is a decorator</summary><br><b>
</b></details> </b>
<b>In python, everything is an object, even functions themselves. Therefore you could pass functions as arguments
for another function eg;
```
def wee(word):
return word
def oh(f):
return f + "Ohh"
>>> oh(wee("Wee"))
<<< Wee Ohh
```
This allows us to control the before execution of any given function and if we added another function as wrapper,
(a function receiving another function that receives a function as parameter) we could also control the after execution.
Sometimes we want to control the before-after execution of many functions and it would get tedious to write
<code> f = function(function_1())</code>
<code> f = function(function_1(function_2(*args)))</code>
every time, that's what decorators do, they introduce syntax to write all of this on the go, using the keyword '@'.
</b>
</details>
<details> <details>
<summary>Can you show how to write and use decorators?</summary><br><b> <summary>Can you show how to write and use decorators?</summary><br><b>
</b></details>
<code>
These two decorators (ntimes and timer) are usually used to display decorators functionalities, you can find them in lots of
tutorials/reviews. I first saw these examples two years ago in pyData 2017. https://www.youtube.com/watch?v=7lmCu8wz8ro&t=3731s</code>
```
Simple decorator:
def deco(f):
print(f"Hi I am the {f.__name__}() function!")
return f
@deco
def hello_world():
return "Hi, I'm in!"
a = hello_world()
print(a)
>>> Hi I am the hello_world() function!
Hi, I'm in!
```
This is the simplest decorator version, it basically saves us from writting <code>a = deco(hello_world())</code>.
But at this point we can only control the before execution, let's take on the after:
```
def deco(f):
def wrapper(*args, **kwargs):
print("Rick Sanchez!")
func = f(*args, **kwargs)
print("I'm in!")
return func
return wrapper
@deco
def f(word):
print(word)
a = f("************")
>>> Rick Sanchez!
************
I'm in!
```
deco receives a function -> f
wrapper receives the arguments -> *args, **kwargs
wrapper returns the function plus the arguments -> f(*args, **kwargs)
deco returns wrapper.
As you can see we conveniently do things before and after the execution of a given function.
For example, we could write a decorator that calculates the execution time of a function.
```
import time
def deco(f):
def wrapper(*args, **kwargs):
before = time.time()
func = f(*args, **kwargs)
after = time.time()
print(after-before)
return func
return wrapper
@deco
def f():
time.sleep(2)
print("************")
a = f()
>>> 2.0008859634399414
```
Or create a decorator that executes a function n times.
```
def n_times(n):
def wrapper(f):
def inner(*args, **kwargs):
for _ in range(n):
func = f(*args, **kwargs)
return func
return inner
return wrapper
@n_times(4)
def f():
print("************")
a = f()
>>>************
************
************
************
```
</b></details>
<details> <details>
<summary>Write a script which will determine if a given host is accessible on a given port</summary><br><b> <summary>Write a script which will determine if a given host is accessible on a given port</summary><br><b>
</b></details> </b></details>