Python basics - classes, attributes, private members and docs

Table of Contents

Python OOP

The most interesting thing in this for me is that Python allow to work with not defined explicitlly attributes. To be honest it stucked me little bit

Attributes

class Point:
	pass

p1 = Point()
p2 = Point()

# So it seems I can make any attribute without
# putting into the class explicitly

p1.x = 5
p1.y = 4

p2.x = 3
p2.y = 6

print(p1.x, p1.y)
print(p2.x, p2.y)

But here’s the trick. I have to manage them myself. I mean I have to be sure that they’re previously initialized before I’m trying to access them (kinda obvious)

Python has initializer for this purpose __init__

If I need to have what C++ programmers called default constructor, I can do this:

class Point:
	__init__(self, x = 0, y = 0):
		self.x = x
		self.y = y

Constructors __new__ is used for metaprogramming (tbc)

Private methods and variables

def _private_method()
def __extra_private_method() #with name mangling

#Same goes to variables, see example below

How to access variable with name mangling

class SecretString:
	def __init__(self, string, pass):
		self.__string = string
		self.__pass = pass
		
	def decrypt(self, pass):
		if(pass == self.__pass):
			return self.__string
		else:
			return ''

secret_str = SecretString("String", "password")
print(secret_string.decrypt("password")) #works fine
print(secret_string.__string) #doesn't work
print(secret_string._SecretString__string) #works yay

Python docs

I can load python docs via python interactive interpretator

Load the file
Print help(class)
```
python -i file.py
help(Point) <enter>
```

Obvious python

Python script runs immediately when imported So all startup code should goes in function (for example main), because accidentally I can run the code when I wanted only the particular function.
Module - it’s a file with python code. Package - is a folder, containing set of modules (files). That’s why we have __init__.py in package =)