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_number “ 10 000 .
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 „ if “ nepravdivý .
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 num
je 11
na 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 True
taká, 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 1
a pokračuje až po ten 11
prvok ( 10
je tým 10
prvkom).
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.
List
je 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. List
má 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 Dictionary
value? 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 Dictionary
keys.
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 Dictionary
I 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 Dictionary
key. Nothing complicated here, right?
Iteration: Looping Through Data Structures
As we learned in the Python Basics, the List
iteration is very simple. We Python
developers 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 Dictionary
key
, 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 init
method. 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 pythonic
getter
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. “ - WikipediaCelá vnútorná reprezentácia objektu je zvonka skrytá. Iba objekt môže interagovať s internými údajmi.
Najprv musíme pochopiť, ako fungujú public
a non-public
inštančné 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_name
inštančnú premennú a tá aktualizovala hodnotu. Také jednoduché. Pretože je to public
premenná, 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 8Ako public instance variable
, môžeme definovať non-public instance variable
oboje v rámci metódy konštruktora alebo v rámci triedy. Rozdiel v syntaxi je: pre non-public instance variables
, _
pred variable
menom použite podčiarkovník ( ) .
_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 email
premennú? 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 variables
sú 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 ( email
a 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 variables
pomocou 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]
- We initiated a new object with
first_name
TK andemail
[email protected] - Printed the email by accessing the
non-public variable
with a method - Tried to set a new
email
out of our class - We need to treat
non-public variable
asnon-public
part of the API - Updated the
non-public variable
with our instance method - 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_age
non-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 methods
sú 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_age
non-public method
a a show_age
public method
. show_age
Môžu využiť nášho objektu (z našej triedy) a _get_age
použiť iba vo vnútri našej definíciu triedy (vnútorná show_age
metóda). 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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