Learning Python: From Zero to Hero

Po prvé, čo je to Python? Podľa jeho tvorcu, Guida van Rossuma, je Python:

„Programovací jazyk na vysokej úrovni a jeho základná filozofia návrhu spočíva v čitateľnosti kódu a syntaxi, ktorá umožňuje programátorom vyjadrovať koncepty v niekoľkých riadkoch kódu.“

Prvý dôvod, prečo som sa naučil Python, bol pre mňa ten, že je v skutočnosti krásnyprogramovací jazyk. Bolo skutočne prirodzené v ňom kódovať a vyjadrovať svoje myšlienky.

Ďalším dôvodom bolo, že kódovanie v Pythone môžeme použiť viacerými spôsobmi: tu svieti žiarenie dát, vývoj webových aplikácií a strojové učenie. Quora, Pinterest a Spotify používajú na vývoj svojho backendového webu Python. Poďme sa teda o tom niečo naučiť.

Základy

1. Premenné

O premenných môžete uvažovať ako o slovách, ktoré uchovávajú hodnotu. Také jednoduché.

V Pythone je skutočne ľahké definovať premennú a nastaviť jej hodnotu. Predstavte si, že chcete uložiť číslo 1 do premennej zvanej „jeden“. Poďme na to:

one = 1

Aké jednoduché to bolo? Práve ste priradili hodnotu 1 k premennej „jeden“.

two = 2 some_number = 10000

A ľubovoľnú inú hodnotu môžete priradiť ľubovoľným ďalším premenným, ktoré chcete. Ako vidíte v tabuľke vyššie, premenná „ two “ uchováva celé číslo 2 a „ some_number10 000 .

Okrem celých čísel môžeme použiť aj logické hodnoty (True / False), reťazce, float a mnoho ďalších dátových typov.

# booleans true_boolean = True false_boolean = False # string my_name = "Leandro Tk" # float book_price = 15.80

2. Tok kontroly: podmienené vyhlásenia

Ak “ používa výraz na vyhodnotenie, či je výrok pravdivý alebo nepravdivý. Ak je to pravda, vykoná to, čo je vo vnútri príkazu „if“. Napríklad:

if True: print("Hello Python If") if 2 > 1: print("2 is greater than 1")

2 je väčšie ako 1 , takže sa vykoná „ tlačový “ kód.

Príkaz „ else “ sa vykoná, ak je výraz „ ifnepravdivý .

if 1 > 2: print("1 is greater than 2") else: print("1 is not greater than 2")

1 nie je väčšie ako 2 , takže sa vykoná kód vo vnútri príkazu „ else “.

Môžete tiež použiť príkaz „ elif “:

if 1 > 2: print("1 is greater than 2") elif 2 > 1: print("1 is not greater than 2") else: print("1 is equal to 2")

3. Opakovanie / opakovanie

V Pythone môžeme iterovať v rôznych formách. Budem hovoriť o dvoch: zatiaľa pre .

While Looping: while the statement is True, the code inside the block will be executed. Tento kód teda vytlačí číslo od 1 do 10 .

num = 1 while num <= 10: print(num) num += 1

Kým slučka potrebuje " podmienku slučky. „Ak zostane pravdivá, bude pokračovať v iterácii. V tomto príklade, keď numje 11na stav slučky rovná False.

Ďalší základný kúsok kódu na lepšie pochopenie:

loop_condition = True while loop_condition: print("Loop Condition keeps: %s" %(loop_condition)) loop_condition = False

Podmienka slučky je Truetaká, aby neustále iterovala - kým ju nenastavíme False.

Pre opakovanie: do bloku použijete premennú „ num “ a príkaz „ for “ ju iteruje. Tento kód sa vytlačí rovnako ako kód while : od 1 do 10 .

for i in range(1, 11): print(i)

Vidíš? Je to také jednoduché. Rozsah začína na 1a pokračuje až po ten 11prvok ( 10je tým 10prvkom).

Zoznam: Zbierka | Pole | Dátová štruktúra

Predstavte si, že chcete celé číslo 1 uložiť do premennej. Ale možno teraz chcete uložiť 2. A 3, 4, 5 ...

Mám iný spôsob uloženia všetkých celých čísel, ktoré chcem, ale nie v miliónoch premenných ? Uhádli ste - existuje skutočne ďalší spôsob, ako ich uložiť.

Listje kolekcia, ktorú je možné použiť na uloženie zoznamu hodnôt (napríklad týchto celých čísel, ktoré chcete). Poďme to teda použiť:

my_integers = [1, 2, 3, 4, 5]

Je to naozaj jednoduché. Vytvorili sme pole a uložili sme ho na my_integer .

Ale možno sa pýtate: „Ako môžem získať hodnotu z tohto poľa?“

Skvelá otázka. Listmá koncept zvaný index . Prvý prvok získa index 0 (nula). Druhý dostane 1 atď. Máte nápad.

Aby sme to objasnili, môžeme predstaviť pole a každý prvok s jeho indexom. Môžem to nakresliť:

Pomocou syntaxe Pythonu je tiež ľahké pochopiť:

my_integers = [5, 7, 1, 3, 4] print(my_integers[0]) # 5 print(my_integers[1]) # 7 print(my_integers[4]) # 4

Predstavte si, že nechcete ukladať celé čísla. Chcete iba uložiť reťazce, napríklad zoznam mien vašich príbuzných. Moja by vyzerala asi takto:

relatives_names = [ "Toshiaki", "Juliana", "Yuji", "Bruno", "Kaio" ] print(relatives_names[4]) # Kaio

Funguje to rovnako ako celé čísla. Pekný.

We just learned how Lists indices work. But I still need to show you how we can add an element to the List data structure (an item to a list).

The most common method to add a new value to a List is append. Let’s see how it works:

bookshelf = [] bookshelf.append("The Effective Engineer") bookshelf.append("The 4 Hour Work Week") print(bookshelf[0]) # The Effective Engineer print(bookshelf[1]) # The 4 Hour Work Week

append is super simple. You just need to apply the element (eg. “The Effective Engineer”) as the append parameter.

Well, enough about Lists. Let’s talk about another data structure.

Dictionary: Key-Value Data Structure

Now we know that Lists are indexed with integer numbers. But what if we don’t want to use integer numbers as indices? Some data structures that we can use are numeric, string, or other types of indices.

Let’s learn about the Dictionary data structure. Dictionary is a collection of key-value pairs. Here’s what it looks like:

dictionary_example = { "key1": "value1", "key2": "value2", "key3": "value3" }

The key is the index pointing to thevalue. How do we access the Dictionaryvalue? You guessed it — using the key. Let’s try it:

dictionary_tk = { "name": "Leandro", "nickname": "Tk", "nationality": "Brazilian" } print("My name is %s" %(dictionary_tk["name"])) # My name is Leandro print("But you can call me %s" %(dictionary_tk["nickname"])) # But you can call me Tk print("And by the way I'm %s" %(dictionary_tk["nationality"])) # And by the way I'm Brazilian

I created a Dictionary about me. My name, nickname, and nationality. Those attributes are the Dictionarykeys.

As we learned how to access the List using index, we also use indices (keys in the Dictionary context) to access the value stored in the Dictionary.

In the example, I printed a phrase about me using all the values stored in the Dictionary. Pretty simple, right?

Another cool thing about Dictionary is that we can use anything as the value. In the DictionaryI created, I want to add the key “age” and my real integer age in it:

dictionary_tk = { "name": "Leandro", "nickname": "Tk", "nationality": "Brazilian", "age": 24 } print("My name is %s" %(dictionary_tk["name"])) # My name is Leandro print("But you can call me %s" %(dictionary_tk["nickname"])) # But you can call me Tk print("And by the way I'm %i and %s" %(dictionary_tk["age"], dictionary_tk["nationality"])) # And by the way I'm Brazilian

Here we have a key (age) value (24) pair using string as the key and integer as the value.

As we did with Lists, let’s learn how to add elements to a Dictionary. The keypointing to avalue is a big part of what Dictionary is. This is also true when we are talking about adding elements to it:

dictionary_tk = { "name": "Leandro", "nickname": "Tk", "nationality": "Brazilian" } dictionary_tk['age'] = 24 print(dictionary_tk) # {'nationality': 'Brazilian', 'age': 24, 'nickname': 'Tk', 'name': 'Leandro'} 

We just need to assign a value to a Dictionarykey. Nothing complicated here, right?

Iteration: Looping Through Data Structures

As we learned in the Python Basics, the List iteration is very simple. We Pythondevelopers commonly use For looping. Let’s do it:

bookshelf = [ "The Effective Engineer", "The 4-hour Workweek", "Zero to One", "Lean Startup", "Hooked" ] for book in bookshelf: print(book)

So for each book in the bookshelf, we (can do everything with it) print it. Pretty simple and intuitive. That’s Python.

For a hash data structure, we can also use the for loop, but we apply the key :

dictionary = { "some_key": "some_value" } for key in dictionary: print("%s --> %s" %(key, dictionary[key])) # some_key --> some_value

This is an example how to use it. For each key in the dictionary , we print the key and its corresponding value.

Another way to do it is to use the iteritems method.

dictionary = { "some_key": "some_value" } for key, value in dictionary.items(): print("%s --> %s" %(key, value)) # some_key --> some_value

We did name the two parameters as key and value, but it is not necessary. We can name them anything. Let’s see it:

dictionary_tk = { "name": "Leandro", "nickname": "Tk", "nationality": "Brazilian", "age": 24 } for attribute, value in dictionary_tk.items(): print("My %s is %s" %(attribute, value)) # My name is Leandro # My nickname is Tk # My nationality is Brazilian # My age is 24

We can see we used attribute as a parameter for the Dictionarykey, and it works properly. Great!

Classes & Objects

A little bit of theory:

Objects are a representation of real world objects like cars, dogs, or bikes. The objects share two main characteristics: data and behavior.

Cars have data, like number of wheels, number of doors, and seating capacity They also exhibit behavior: they can accelerate, stop, show how much fuel is left, and so many other things.

We identify data as attributes and behavior as methods in object-oriented programming. Again:

Data → Attributes and Behavior → Methods

And a Class is the blueprint from which individual objects are created. In the real world, we often find many objects with the same type. Like cars. All the same make and model (and all have an engine, wheels, doors, and so on). Each car was built from the same set of blueprints and has the same components.

Python Object-Oriented Programming mode: ON

Python, as an Object-Oriented programming language, has these concepts: class and object.

A class is a blueprint, a model for its objects.

So again, a class it is just a model, or a way to define attributes and behavior (as we talked about in the theory section). As an example, a vehicle class has its own attributes that define what objects are vehicles. The number of wheels, type of tank, seating capacity, and maximum velocity are all attributes of a vehicle.

With this in mind, let’s look at Python syntax for classes:

class Vehicle: pass

We define classes with a class statement — and that’s it. Easy, isn’t it?

Objects are instances of a class. We create an instance by naming the class.

car = Vehicle() print(car) # 

Here car is an object (or instance) of the classVehicle.

Remember that our vehicle class has four attributes: number of wheels, type of tank, seating capacity, and maximum velocity. We set all these attributes when creating a vehicle object. So here, we define our class to receive data when it initiates it:

class Vehicle: def __init__(self, number_of_wheels, type_of_tank, seating_capacity, maximum_velocity): self.number_of_wheels = number_of_wheels self.type_of_tank = type_of_tank self.seating_capacity = seating_capacity self.maximum_velocity = maximum_velocity

We use the initmethod. We call it a constructor method. So when we create the vehicle object, we can define these attributes. Imagine that we love the Tesla Model S, and we want to create this kind of object. It has four wheels, runs on electric energy, has space for five seats, and the maximum velocity is 250km/hour (155 mph). Let’s create this object:

tesla_model_s = Vehicle(4, 'electric', 5, 250)

Four wheels + electric “tank type” + five seats + 250km/hour maximum speed.

All attributes are set. But how can we access these attributes’ values? We send a message to the object asking about them. We call it a method. It’s the object’s behavior. Let’s implement it:

class Vehicle: def __init__(self, number_of_wheels, type_of_tank, seating_capacity, maximum_velocity): self.number_of_wheels = number_of_wheels self.type_of_tank = type_of_tank self.seating_capacity = seating_capacity self.maximum_velocity = maximum_velocity def number_of_wheels(self): return self.number_of_wheels def set_number_of_wheels(self, number): self.number_of_wheels = number

This is an implementation of two methods: number_of_wheels and set_number_of_wheels. We call it getter & setter. Because the first gets the attribute value, and the second sets a new value for the attribute.

In Python, we can do that using @property (decorators) to define getters and setters. Let’s see it with code:

class Vehicle: def __init__(self, number_of_wheels, type_of_tank, seating_capacity, maximum_velocity): self.number_of_wheels = number_of_wheels self.type_of_tank = type_of_tank self.seating_capacity = seating_capacity self.maximum_velocity = maximum_velocity @property def number_of_wheels(self): return self.__number_of_wheels @number_of_wheels.setter def number_of_wheels(self, number): self.__number_of_wheels = number

And we can use these methods as attributes:

tesla_model_s = Vehicle(4, 'electric', 5, 250) print(tesla_model_s.number_of_wheels) # 4 tesla_model_s.number_of_wheels = 2 # setting number of wheels to 2 print(tesla_model_s.number_of_wheels) # 2

This is slightly different than defining methods. The methods work as attributes. For example, when we set the new number of wheels, we don’t apply two as a parameter, but set the value 2 to number_of_wheels. This is one way to write pythonicgetter and setter code.

But we can also use methods for other things, like the “make_noise” method. Let’s see it:

class Vehicle: def __init__(self, number_of_wheels, type_of_tank, seating_capacity, maximum_velocity): self.number_of_wheels = number_of_wheels self.type_of_tank = type_of_tank self.seating_capacity = seating_capacity self.maximum_velocity = maximum_velocity def make_noise(self): print('VRUUUUUUUM')

Keď zavoláme túto metódu, vráti iba reťazec VRRRRUUUUM.

tesla_model_s = Vehicle(4, 'electric', 5, 250) tesla_model_s.make_noise() # VRUUUUUUUM

Zapuzdrenie: skrytie informácií

Zapuzdrenie je mechanizmus, ktorý obmedzuje priamy prístup k údajom a metódam objektov. Zároveň to však uľahčuje prácu s týmito údajmi (metódy objektov).

„Zapuzdrenie možno použiť na skrytie dátových členov a funkcie členov. Podľa tejto definície znamená zapuzdrenie, že vnútorná reprezentácia objektu je všeobecne skrytá pred pohľadom mimo definíciu objektu. “ - Wikipedia

Celá vnútorná reprezentácia objektu je zvonka skrytá. Iba objekt môže interagovať s internými údajmi.

Najprv musíme pochopiť, ako fungujú publica non-publicinštančné premenné a metódy.

Premenné inštancie

For a Python class, we can initialize a public instance variable within our constructor method. Let’s see this:

Within the constructor method:

class Person: def __init__(self, first_name): self.first_name = first_name

Here we apply the first_name value as an argument to the public instance variable.

tk = Person('TK') print(tk.first_name) # => TK

Within the class:

class Person: first_name = 'TK'

Here, we do not need to apply the first_name as an argument, and all instance objects will have a class attribute initialized with TK.

tk = Person() print(tk.first_name) # => TK

Cool. We have now learned that we can use public instance variables and class attributes. Another interesting thing about the public part is that we can manage the variable value. What do I mean by that? Our object can manage its variable value: Get and Set variable values.

Keeping the Person class in mind, we want to set another value to its first_name variable:

tk = Person('TK') tk.first_name = 'Kaio' print(tk.first_name) # => Kaio

Ideme na to. Iba sme nastavili inú hodnotu ( kaio) na first_nameinštančnú premennú a tá aktualizovala hodnotu. Také jednoduché. Pretože je to publicpremenná, môžeme to urobiť.

Premenná neverejnej inštancie

Nepoužívame tu výraz „súkromné“, pretože žiadny atribút nie je v Pythone skutočne súkromný (bez všeobecne zbytočného množstva práce). - PEP 8

Ako public instance variable, môžeme definovať non-public instance variableoboje v rámci metódy konštruktora alebo v rámci triedy. Rozdiel v syntaxi je: pre non-public instance variables, _pred variablemenom použite podčiarkovník ( ) .

„Premenné inštancie 'Súkromné', ku ktorým nie je možné získať prístup inak, ako z vnútra objektu, v Pythone neexistujú. Existuje však konvencia, ktorou sa riadi väčšina kódu Pythonu: meno s predponou (napríklad _spam) by sa malo považovať za neverejnú súčasť API (či už je to funkcia, metóda alebo dátový člen) “ - Python Software Foundation

Tu je príklad:

class Person: def __init__(self, first_name, email): self.first_name = first_name self._email = email

Videli ste emailpremennú? Takto definujeme non-public variable:

tk = Person('TK', '[email protected]') print(tk._email) # [email protected]
Máme k nej prístup a môžeme ju aktualizovať. Non-public variablessú iba konvenciou a malo by sa s nimi zaobchádzať ako s neverejnou súčasťou API.

Používame teda metódu, ktorá nám to umožňuje v rámci našej definície triedy. Implementujme dve metódy ( emaila update_email) na jej pochopenie:

class Person: def __init__(self, first_name, email): self.first_name = first_name self._email = email def update_email(self, new_email): self._email = new_email def email(self): return self._email

Teraz môžeme non-public variablespomocou týchto metód aktualizovať a pristupovať k nim. Pozrime sa:

tk = Person('TK', '[email protected]') print(tk.email()) # => [email protected] # tk._email = '[email protected]' -- treat as a non-public part of the class API print(tk.email()) # => [email protected] tk.update_email('[email protected]') print(tk.email()) # => [email protected]
  1. We initiated a new object with first_name TK and email [email protected]
  2. Printed the email by accessing the non-public variable with a method
  3. Tried to set a new email out of our class
  4. We need to treat non-public variable as non-public part of the API
  5. Updated the non-public variable with our instance method
  6. Success! We can update it inside our class with the helper method

Public Method

With public methods, we can also use them out of our class:

class Person: def __init__(self, first_name, age): self.first_name = first_name self._age = age def show_age(self): return self._age

Let’s test it:

tk = Person('TK', 25) print(tk.show_age()) # => 25

Great — we can use it without any problem.

Non-public Method

But with non-public methods we aren’t able to do it. Let’s implement the same Person class, but now with a show_agenon-public method using an underscore (_).

class Person: def __init__(self, first_name, age): self.first_name = first_name self._age = age def _show_age(self): return self._age

And now, we’ll try to call this non-public method with our object:

tk = Person('TK', 25) print(tk._show_age()) # => 25
Máme k nej prístup a môžeme ju aktualizovať. Non-public methodssú iba konvenciou a malo by sa s nimi zaobchádzať ako s neverejnou súčasťou API.

Tu je príklad toho, ako to môžeme použiť:

class Person: def __init__(self, first_name, age): self.first_name = first_name self._age = age def show_age(self): return self._get_age() def _get_age(self): return self._age tk = Person('TK', 25) print(tk.show_age()) # => 25

Tu máme _get_agenon-public methoda a show_agepublic method. show_ageMôžu využiť nášho objektu (z našej triedy) a _get_agepoužiť iba vo vnútri našej definíciu triedy (vnútorná show_agemetóda). Ale zase: ako vec dohovoru.

Zhrnutie zapuzdrenia

Pomocou zapuzdrenia môžeme zabezpečiť, aby vnútorná reprezentácia objektu bola zvonka skrytá.

Dedenie: správanie a vlastnosti

Niektoré objekty majú spoločné niektoré veci: svoje správanie a vlastnosti.

Napríklad som zdedil niektoré vlastnosti a správanie po svojom otcovi. Zdedil som jeho oči a vlasy ako vlastnosti a jeho netrpezlivosť a uzavretosť ako správanie.

In object-oriented programming, classes can inherit common characteristics (data) and behavior (methods) from another class.

Let’s see another example and implement it in Python.

Imagine a car. Number of wheels, seating capacity and maximum velocity are all attributes of a car. We can say that anElectricCar class inherits these same attributes from the regular Car class.

class Car: def __init__(self, number_of_wheels, seating_capacity, maximum_velocity): self.number_of_wheels = number_of_wheels self.seating_capacity = seating_capacity self.maximum_velocity = maximum_velocity

Our Car class implemented:

my_car = Car(4, 5, 250) print(my_car.number_of_wheels) print(my_car.seating_capacity) print(my_car.maximum_velocity)

Once initiated, we can use all instance variables created. Nice.

In Python, we apply a parent class to the child class as a parameter. An ElectricCar class can inherit from our Car class.

class ElectricCar(Car): def __init__(self, number_of_wheels, seating_capacity, maximum_velocity): Car.__init__(self, number_of_wheels, seating_capacity, maximum_velocity)

Simple as that. We don’t need to implement any other method, because this class already has it (inherited from Car class). Let’s prove it:

my_electric_car = ElectricCar(4, 5, 250) print(my_electric_car.number_of_wheels) # => 4 print(my_electric_car.seating_capacity) # => 5 print(my_electric_car.maximum_velocity) # => 250

Beautiful.

That’s it!

We learned a lot of things about Python basics:

  • How Python variables work
  • How Python conditional statements work
  • How Python looping (while & for) works
  • How to use Lists: Collection | Array
  • Dictionary Key-Value Collection
  • How we can iterate through these data structures
  • Objects and Classes
  • Attributes as objects’ data
  • Methods as objects’ behavior
  • Using Python getters and setters & property decorator
  • Encapsulation: hiding information
  • Inheritance: behaviors and characteristics

Congrats! You completed this dense piece of content about Python.

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