List Comprehensions in Python

• List comprehension methods are an elegant way to create and manage lists.
• List comprehensions are a more compact way of creating lists.
• More flexible than for loops, list comprehension is usually faster than other methods.

Example 1:

# my_new_list = [ expression for item in list ]
digits = [x for x in range(10)]
print (digits)

output

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Example 2:

# create a list with list comprehensions
multiples_of_three = [ x*3 for x in range(10) ]

print(multiples_of_three)

[0, 3, 6, 9, 12, 15, 18, 21, 24, 27]

Example 3:

# use list comprehension to print the letters in a string
letters = [ letter for letter in "20,000 Leagues Under The Sea"]

print(letters)

output:

['2', '0', ',', '0', '0', '0', ' ', 'L', 'e', 'a', 'g', 'u', 'e', 's',
' ', 'U', 'n', 'd', 'e', 'r', ' ', 'T', 'h', 'e', ' ', 'S', 'e', 'a']

Primer on Python Decorators

Functions

a function returns a value based on the given arguments.

• First-Class Objects: In Python, functions are first-class objects. This means that functions can be passed around and used as arguments,
  just like any other object (string, int, float, list, and so on).

• Inner Functions: define functions inside other functions. Such functions are called inner functions.

• Returning Functions From Functions: Python also allows you to use functions as return values.

• Simple Decorators

  decorators wrap a function, modifying its behavior

• Syntactic Sugar: use decorators in a simpler way with the @ symbol

• Reusing Decorators: a decorator is just a regular Python function.
• Decorating Functions With Arguments

  def do_twice(func):
    def wrapper_do_twice(*args, **kwargs):
        func(*args, **kwargs)
        func(*args, **kwargs)
    return wrapper_do_twice
  

• Returning Values From Decorated Functions: make sure the wrapper function returns the return value of the decorated function.

Fancy Decorators

• Decorating Classes: decor the whole class or decor the functions in class
• Nesting Decorators ```angular2html from decorators import debug, do_twice

@debug @do_twice def greet(name): print(f”Hello {name}”)

- Decorators With Arguments
```angular2html
@repeat(num_times=4)
def greet(name):
    print(f"Hello {name}")

• Stateful Decorators

  pure functions returning a value based on given arguments. Stateful decorators are quite the opposite, where the return 
  value will depend on the current state, as well as the given arguments.