Game of Greed 3

List Comprehensions

Basically Python list comprehensions powerful and essential method to use, they are used to make your code more readable and eaiser to understand.

• faster than other methods.
• better than using for loops regarding to flexibility.
• you can add conditional statements in the form of filters.

Syntax

my_new_list = [ expression for item in list ]

Range() method

• using range() in comprehension lists:

  digits = [x for x in range(10)]
  

  output of printing digits –> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

• using comprehension lists to doublicate a range of numers:

  squares = [x**2 for x in range(10)]
  

• using comprehension lists to find even numbers in a range of numers:

  even_numbers = [ x for x in range(1,20) if x % 2 == 0]
  

• using comprehension lists to print first letter of each author: authors = [“Ernest Hemingway”,”Langston Hughes”,”Frank Herbert”,”Toni Morrison”, “Emily Dickson”,”Stephen King”]

  letters = [name[0] for name in authors]
  

• use list comprehension to print the letters in a string:

  letters = [ letter for letter in "20,000 Leagues Under The Sea"]
  

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

lower() and upper() methods

• Changing a letter’s case:

  lower_case = [ letter.lower() for letter in ['A','B','C'] ]
  upper_case = [ letter.upper() for letter in ['a','b','c'] ]
  

isdigit() method

• to extract numbers from letters:

  user_data = "Elvis Presley 987-654-3210"
  phone_number = [ x for x in user_data if x.isdigit()]
  

  output –> list in which each element represents a number from the string above.

Parsing files

Using list comprehension, we can iterate through the lines of text in the file and store their contents in a new list.

file = open("dreams.txt", 'r')
poem = [ line for line in file ]

for line in poem:
    print(line)

output –> Hold fast to dreams

For if dreams die

Life is a broken-winged bird

That cannot fly.

-Langston Hughs

Functions

• Adding arguments to list comprehension ``` def double(x): return x*2

nums = [double(x) for x in range(1,10)] print(nums)

- we can add a condition to the previous for doubling only even numbers:

even_nums = [double(x) for x in range(1,10) if x%2 == 0]

- Additional arguments can be added to create more complex logic:

nums = [x+y for x in [1,2,3] for y in [10,20,30]] ``` output –> [11, 21, 31, 12, 22, 32, 13, 23, 33]

More

Primer on Python Decorators

Decorators provide a simple syntax for calling higher-order functions.

• First-Class Objects functions are first-class objects. This means that functions can be passed around and used as arguments

• Inner Functions they are functions inside other functions, the inner functions are not defined until the parent function is called, the printing only happens when the inner functions are executed.

More on decorators