V tomto tutoriále sa dozviete o premenných, konštantách, literáloch Pythonu a ich prípadoch použitia.
Video: Premenné Pythonu a tlač ()
Premenné Pythonu
Premenná je pomenované umiestnenie, ktoré sa používa na ukladanie údajov do pamäte. Je užitočné uvažovať o premenných ako o kontajneri, ktorý obsahuje údaje, ktoré je možné neskôr v programe zmeniť. Napríklad,
number = 10
Tu sme vytvorili premennú s názvom number. Premennej sme priradili hodnotu 10.
Premenné si môžete predstaviť ako tašku na uloženie kníh a knihu je možné kedykoľvek vymeniť.
number = 10 number = 1.1
Spočiatku bola hodnota čísla 10. Neskôr sa zmenila na 1,1.
Poznámka : V Pythone vlastne nepriraďujeme hodnoty premenným. Namiesto toho Python dáva odkaz na objekt (hodnotu) na premennú.
Priradenie hodnôt k premenným v Pythone
Ako vidíte z vyššie uvedeného príkladu, =na priradenie hodnoty k premennej môžete použiť operátor priradenia.
Príklad 1: Deklarácia a priradenie hodnoty premennej
website = "apple.com" print(website)
Výkon
apple.com
Vo vyššie uvedenom programe sme premennej webovej stránke priradili hodnotu apple.com. Potom sme vytlačili hodnotu priradenú k webu tj apple.com
Poznámka : Python je jazyk odvodený od typu, takže nemusíte explicitne definovať typ premennej. Automaticky vie, že apple.com je reťazec, a deklaruje premennú webu ako reťazec.
Príklad 2: Zmena hodnoty premennej
website = "apple.com" print(website) # assigning a new value to website website = "programiz.com" print(website)
Výkon
apple.com programiz.com
Vo vyššie uvedenom programe sme pôvodne priradili apple.com k premennej webovej stránky. Potom sa hodnota zmení na programiz.com.
Príklad 3: Priradenie viacerých hodnôt viacerým premenným
a, b, c = 5, 3.2, "Hello" print (a) print (b) print (c)
Ak chceme priradiť rovnakú hodnotu viacerým premenným naraz, môžeme to urobiť takto:
x = y = z = "same" print (x) print (y) print (z)
Druhý program priradí všetkým trom premenným x, yaz rovnaký reťazec.
Konštanty
Konštanta je typ premennej, ktorej hodnotu nie je možné zmeniť. Je užitočné myslieť na konštanty ako na kontajnery, ktoré obsahujú informácie, ktoré sa neskôr nedajú zmeniť.
Konštanty si môžete predstaviť ako tašku na uloženie niektorých kníh, ktoré už po vložení do tašky nemožno vymeniť.
Priradenie hodnoty konštante v Pythone
V Pythone sú konštanty zvyčajne deklarované a priradené v module. Tu je modul nový súbor obsahujúci premenné, funkcie atď., Ktorý sa importuje do hlavného súboru. Vo vnútri modulu sú konštanty napísané veľkými písmenami a podčiarknutiami, ktoré slová oddeľujú.
Príklad 3: Deklarovanie a priraďovanie hodnoty konštante
Vytvorte konštantný.py :
PI = 3.14 GRAVITY = 9.8
Vytvorte main.py :
import constant print(constant.PI) print(constant.GRAVITY)
Výkon
3,14 9,8
Vo vyššie uvedenom programe vytvoríme súbor modulu constant.py . Potom priradíme konštantnú hodnotu PI a GRAVITY. Potom vytvoríme súbor main.py a importujeme constantmodul. Nakoniec vytlačíme konštantnú hodnotu.
Note: In reality, we don't use constants in Python. Naming them in all capital letters is a convention to separate them from variables, however, it does not actually prevent reassignment.
Rules and Naming Convention for Variables and constants
- Constant and variable names should have a combination of letters in lowercase (a to z) or uppercase (A to Z) or digits (0 to 9) or an underscore (_). For example:
snake_case MACRO_CASE camelCase CapWords
- Create a name that makes sense. For example, vowel makes more sense than v.
- If you want to create a variable name having two words, use underscore to separate them. For example:
my_name current_salary
- Use capital letters possible to declare a constant. For example:
PI G MASS SPEED_OF_LIGHT TEMP
- Never use special symbols like !, @, #, $, %, etc.
- Don't start a variable name with a digit.
Literals
Literal is a raw data given in a variable or constant. In Python, there are various types of literals they are as follows:
Numeric Literals
Numeric Literals are immutable (unchangeable). Numeric literals can belong to 3 different numerical types: Integer, Float, and Complex.
Example 4: How to use Numeric literals in Python?
a = 0b1010 #Binary Literals b = 100 #Decimal Literal c = 0o310 #Octal Literal d = 0x12c #Hexadecimal Literal #Float Literal float_1 = 10.5 float_2 = 1.5e2 #Complex Literal x = 3.14j print(a, b, c, d) print(float_1, float_2) print(x, x.imag, x.real)
Output
10 100 200 300 10.5 150.0 3.14j 3.14 0.0
In the above program,
- We assigned integer literals into different variables. Here, a is binary literal, b is a decimal literal, c is an octal literal and d is a hexadecimal literal.
- When we print the variables, all the literals are converted into decimal values.
- 10.5 and 1.5e2 are floating-point literals. 1.5e2 is expressed with exponential and is equivalent to 1.5 * 102.
- We assigned a complex literal i.e 3.14j in variable x. Then we use imaginary literal (x.imag) and real literal (x.real) to create imaginary and real parts of complex numbers.
To learn more about Numeric Literals, refer to Python Numbers.
String literals
A string literal is a sequence of characters surrounded by quotes. We can use both single, double, or triple quotes for a string. And, a character literal is a single character surrounded by single or double quotes.
Example 7: How to use string literals in Python?
strings = "This is Python" char = "C" multiline_str = """This is a multiline string with more than one line code.""" unicode = u"u00dcnicu00f6de" raw_str = r"raw string" print(strings) print(char) print(multiline_str) print(unicode) print(raw_str)
Output
This is Python C This is a multiline string with more than one line code. Ünicöde raw string
In the above program, This is Python is a string literal and C is a character literal.
The value in triple-quotes """ assigned to the multiline_str is a multi-line string literal.
The string u"u00dcnicu00f6de" is a Unicode literal which supports characters other than English. In this case, u00dc represents Ü and u00f6 represents ö.
r"raw string" is a raw string literal.
Boolean literals
A Boolean literal can have any of the two values: True or False.
Example 8: How to use boolean literals in Python?
x = (1 == True) y = (1 == False) a = True + 4 b = False + 10 print("x is", x) print("y is", y) print("a:", a) print("b:", b)
Output
x is True y is False a: 5 b: 10
In the above program, we use boolean literal True and False. In Python, True represents the value as 1 and False as 0. The value of x is True because 1 is equal to True. And, the value of y is False because 1 is not equal to False.
Similarly, we can use the True and False in numeric expressions as the value. The value of a is 5 because we add True which has a value of 1 with 4. Similarly, b is 10 because we add the False having value of 0 with 10.
Special literals
Python contains one special literal i.e. None. We use it to specify that the field has not been created.
Example 9: How to use special literals in Python?
drink = "Available" food = None def menu(x): if x == drink: print(drink) else: print(food) menu(drink) menu(food)
Output
Available None
In the above program, we define a menu function. Inside menu, when we set the argument as drink then, it displays Available. And, when the argument is food, it displays None.
Literal Collections
There are four different literal collections List literals, Tuple literals, Dict literals, and Set literals.
Example 10: How to use literals collections in Python?
fruits = ("apple", "mango", "orange") #list numbers = (1, 2, 3) #tuple alphabets = ('a':'apple', 'b':'ball', 'c':'cat') #dictionary vowels = ('a', 'e', 'i' , 'o', 'u') #set print(fruits) print(numbers) print(alphabets) print(vowels)
Output
('apple', 'mango', 'orange') (1, 2, 3) ('a': 'apple', 'b': 'ball', 'c': 'cat') ('e', 'a', 'o', 'i', 'u')
In the above program, we created a list of fruits, a tuple of numbers, a dictionary dict having values with keys designated to each value and a set of vowels.
To learn more about literal collections, refer to Python Data Types.
