Belajar Python: Dari Nol menjadi Pahlawan

Pertama-tama, apa itu Python? Menurut penciptanya, Guido van Rossum, Python adalah:

"Bahasa pemrograman tingkat tinggi, dan filosofi desain intinya adalah tentang keterbacaan kode dan sintaksis yang memungkinkan pemrogram mengekspresikan konsep dalam beberapa baris kode."

Bagi saya, alasan pertama untuk belajar Python adalah, faktanya, itu indahbahasa pemrograman. Sangat alami untuk membuat kode di dalamnya dan mengekspresikan pikiran saya.

Alasan lainnya adalah kita dapat menggunakan pengkodean dengan Python dalam berbagai cara: ilmu data, pengembangan web, dan pembelajaran mesin semuanya bersinar di sini. Quora, Pinterest, dan Spotify semuanya menggunakan Python untuk pengembangan web backend mereka. Jadi mari kita pelajari sedikit tentang itu.

Dasar

1. Variabel

Anda dapat menganggap variabel sebagai kata-kata yang menyimpan nilai. Sederhana seperti itu.

Dengan Python, sangat mudah untuk mendefinisikan variabel dan mengatur nilainya. Bayangkan Anda ingin menyimpan angka 1 dalam variabel yang disebut "satu". Ayo lakukan:

one = 1

Seberapa sederhana itu? Anda baru saja menetapkan nilai 1 ke variabel "satu".

two = 2 some_number = 10000

Dan Anda dapat menetapkan nilai lain apa pun ke variabel lain apa pun yang Anda inginkan. Seperti yang Anda lihat pada tabel di atas, variabel " dua " menyimpan bilangan bulat 2 , dan " bilangan_berapa " menyimpan 10.000 .

Selain integer, kita juga bisa menggunakan boolean (True / False), string, float, dan banyak tipe data lainnya.

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

2. Arus Kontrol: pernyataan bersyarat

Jika ” menggunakan ekspresi untuk mengevaluasi apakah pernyataan itu Benar atau Salah. Jika Benar, ia mengeksekusi apa yang ada di dalam pernyataan "jika". Sebagai contoh:

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

2 lebih besar dari 1 , jadi kode " cetak " dijalankan.

Pernyataan " else " akan dieksekusi jika ekspresi " jika " salah .

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

1 tidak lebih besar dari 2 , jadi kode di dalam pernyataan " else " akan dieksekusi.

Anda juga dapat menggunakan pernyataan " 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. Perulangan / Iterator

Dengan Python, kita dapat melakukan iterasi dalam berbagai bentuk. Saya akan berbicara tentang dua: sementaradan untuk .

While Looping: sementara pernyataannya Benar, kode di dalam blok akan dieksekusi. Jadi, kode ini akan mencetak angka dari 1 hingga 10 .

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

The sementara lingkaran membutuhkan “ kondisi loop. ”Jika tetap True, itu terus berulang. Dalam contoh ini, ketika numadalah 11yang kondisi loop sederajat False.

Sedikit kode dasar lainnya untuk lebih memahaminya:

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

The kondisi loop adalah Truesehingga membuat iterasi - sampai kita set ke False.

Untuk Pendauran : Anda menerapkan variabel " num " ke blok, dan pernyataan " untuk " akan mengulanginya untuk Anda. Kode ini akan mencetak sama seperti kode while : dari 1 hingga 10 .

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

Lihat? Ini sangat sederhana. Rentang dimulai dengan 1dan berlanjut hingga 11elemen ke ( 10adalah 10elemen ke).

Daftar: Koleksi | Array | Struktur data

Bayangkan Anda ingin menyimpan integer 1 dalam sebuah variabel. Tapi mungkin sekarang Anda ingin menyimpan 2. Dan 3, 4, 5…

Apakah saya memiliki cara lain untuk menyimpan semua bilangan bulat yang saya inginkan, tetapi tidak dalam jutaan variabel ? Anda dapat menebaknya - memang ada cara lain untuk menyimpannya.

Listadalah kumpulan yang dapat digunakan untuk menyimpan daftar nilai (seperti bilangan bulat yang Anda inginkan). Jadi mari kita gunakan:

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

Ini sangat sederhana. Kami membuat sebuah array dan menyimpannya di my_integer .

Tetapi mungkin Anda bertanya: "Bagaimana saya bisa mendapatkan nilai dari larik ini?"

Pertanyaan bagus. Listmemiliki konsep yang disebut indeks . Elemen pertama mendapatkan indeks 0 (nol). Yang kedua mendapat 1, dan seterusnya. Anda mengerti.

Untuk membuatnya lebih jelas, kita dapat merepresentasikan array dan setiap elemen dengan indeksnya. Saya bisa menggambarnya:

Menggunakan sintaks Python, itu juga mudah dipahami:

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

Bayangkan Anda tidak ingin menyimpan bilangan bulat. Anda hanya ingin menyimpan string, seperti daftar nama kerabat Anda. Punyaku akan terlihat seperti ini:

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

Ini bekerja dengan cara yang sama seperti integer. Bagus.

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')

Ketika kita memanggil metode ini, itu hanya mengembalikan string VRRRRUUUUM.

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

Enkapsulasi: Menyembunyikan Informasi

Enkapsulasi adalah mekanisme yang membatasi akses langsung ke data dan metode objek. Tetapi pada saat yang sama, ini memfasilitasi operasi pada data itu (metode objek).

“Enkapsulasi dapat digunakan untuk menyembunyikan data anggota dan fungsi anggota. Di bawah definisi ini, enkapsulasi berarti bahwa representasi internal suatu objek umumnya tersembunyi dari tampilan di luar definisi objek. " - Wikipedia

Semua representasi internal suatu objek disembunyikan dari luar. Hanya objek yang dapat berinteraksi dengan data internalnya.

Pertama, kita perlu memahami bagaimana publicdan non-publiccontoh variabel dan metode bekerja.

Variabel Instans Publik

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

Ini dia. Kami baru saja menetapkan nilai lain ( kaio) ke first_namevariabel instance dan itu memperbarui nilainya. Sederhana seperti itu. Karena ini publicvariabel, kita bisa melakukannya.

Variabel Instans Non-publik

Kami tidak menggunakan istilah "pribadi" di sini, karena tidak ada atribut yang benar-benar pribadi di Python (tanpa jumlah pekerjaan yang umumnya tidak perlu). - PEP 8

Sebagai public instance variable, kita dapat mendefinisikan non-public instance variablekeduanya di dalam metode konstruktor atau di dalam kelas. Perbedaan sintaksnya adalah: untuk non-public instance variables, gunakan garis bawah ( _) sebelum variablenama.

"Variabel instance 'Private' yang tidak dapat diakses kecuali dari dalam objek tidak ada di Python. Namun, ada konvensi yang diikuti oleh sebagian besar kode Python: nama yang diawali dengan garis bawah (misalnya _spam) harus diperlakukan sebagai bagian non-publik dari API (apakah itu fungsi, metode, atau anggota data) ” - Yayasan Perangkat Lunak Python

Berikut contohnya:

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

Apakah Anda melihat emailvariabelnya? Beginilah cara kami mendefinisikan non-public variable:

tk = Person('TK', '[email protected]') print(tk._email) # [email protected]
Kami dapat mengakses dan memperbaruinya. Non-public variableshanyalah konvensi dan harus diperlakukan sebagai bagian non-publik dari API.

Jadi kami menggunakan metode yang memungkinkan kami melakukannya di dalam definisi kelas kami. Mari terapkan dua metode ( emaildan update_email) untuk memahaminya:

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

Sekarang kita dapat memperbarui dan mengakses non-public variablesmenggunakan metode tersebut. Ayo lihat:

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
Kami dapat mengakses dan memperbaruinya. Non-public methodshanyalah konvensi dan harus diperlakukan sebagai bagian non-publik dari API.

Berikut adalah contoh bagaimana kita dapat menggunakannya:

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

Di sini kami memiliki a _get_agenon-public methoddan a show_agepublic method. The show_agedapat digunakan oleh objek kita (dari kelas kami) dan _get_agehanya digunakan di dalam definisi kelas kami (dalam show_agemetode). Tapi sekali lagi: sebagai masalah konvensi.

Ringkasan Enkapsulasi

Dengan enkapsulasi kita dapat memastikan bahwa representasi internal dari objek tersebut tersembunyi dari luar.

Warisan: perilaku dan karakteristik

Objek tertentu memiliki beberapa kesamaan: perilaku dan karakteristiknya.

Misalnya, saya mewarisi beberapa karakteristik dan perilaku dari ayah saya. Saya mewarisi mata dan rambutnya sebagai karakteristik, dan ketidaksabaran serta sikap introversi sebagai perilaku.

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

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