Python notes(1)

List, tuple, dictionary, set

• List: [‘apple’, ‘pear’, ‘orange’]; can be multi-dimensional;
• tuple: (‘apple’, ‘pear’, ‘orange’); immutable; ordered;
• dictionary: {‘apple’:2, ‘pear’:3, ‘orange’:5}; key-value map;
• set: {‘a’, ‘b’, ‘c’, ‘d’}; unordered; no duplicates;

Hiding Data

Weakly private attributes and methods are named using _attibute or _method convention. Weakly private variables CAN be accessed from outside of class. from module import * won’t import variables named as _variable.

Strongly private attributes are named using __attribute. They can not be accessed directly from outside class. To access variable __a of class b from outside class, syntax _b__a should be used.

Lambda

   #named function
   def polynomial(x):
       return x**2 + 7*x + 2
   print(polynomial(-4))
   
   #lambda
   print((lambda x: x**2 + 7*x + 2) (-4))

Decorators

Rudimentary way:

def decor(func):
  def wrap():
    print("============")
    func()
    print("============")
  return wrap

def print_text():
  print("Hello world!")

decorated = decor(print_text)
decorated()

Elegant way:

def decor(func):
    def wrap():
        print("============")
        func()
        print("============")
    return wrap

@decor
def print_text():
    print("Hello world!")

print_text();

Class method

Class method is called by a class, instead of an instance of that class, and returns an object, in the following example, a “cls” object. Technically, “self” or “cls” can be changed to anything else. But everyone follows this convention.

class Rectangle:
    def __init__(self, width, height):
        self.width = width
        self.height = height

    def calculate_area(self):
        return self.width * self.height

    @classmethod
    def new_square(cls, side_length):
        return cls(side_length, side_length)

square = Rectangle.new_square(5)
print(square.calculate_area())

Static method

Does not receive any additional arguments. Marked with @staticmethod decorator.