U ovom vodiču naučit ćete o Python varijablama, konstantama, literalima i njihovim slučajevima upotrebe.
Video: Python varijable i ispis ()
Python varijable
Varijabla je imenovano mjesto koje se koristi za pohranu podataka u memoriju. Korisno je o varijablama razmišljati kao o spremniku koji sadrži podatke koji se kasnije mogu mijenjati u programu. Na primjer,
number = 10
Ovdje smo stvorili varijablu s imenom broj. Varijabli smo dodijelili vrijednost 10.
Varijable možete smatrati torbom za pohranu knjiga u nju i tu knjigu možete zamijeniti u bilo kojem trenutku.
number = 10 number = 1.1
U početku je vrijednost broja bila 10. Kasnije je promijenjena u 1.1.
Napomena : U Pythonu zapravo ne dodjeljujemo vrijednosti varijablama. Umjesto toga, Python daje referencu objekta (vrijednosti) na varijablu.
Dodjeljivanje vrijednosti varijablama u Pythonu
Kao što možete vidjeti iz gornjeg primjera, možete koristiti operator dodjele =za dodjeljivanje vrijednosti varijabli.
Primjer 1: Deklariranje i dodjeljivanje vrijednosti varijabli
website = "apple.com" print(website)
Izlaz
apple.com
U gore navedenom programu varijabli web mjestu dodijelili smo vrijednost apple.com. Zatim smo ispisali vrijednost dodijeljenu web stranici tj. Apple.com
Napomena : Python je jezik o kojem se govori, pa ne morate eksplicitno definirati tip varijable. Automatski zna da je apple.com niz i varijablu web mjesta proglašava nizom.
Primjer 2: Promjena vrijednosti varijable
website = "apple.com" print(website) # assigning a new value to website website = "programiz.com" print(website)
Izlaz
apple.com programiz.com
U gore navedenom programu prvotno smo dodijelili apple.com varijabli web mjesta. Zatim se vrijednost mijenja u programiz.com.
Primjer 3: Dodjela višestrukih vrijednosti višestrukim varijablama
a, b, c = 5, 3.2, "Hello" print (a) print (b) print (c)
Ako želimo dodijeliti istu vrijednost više varijabli odjednom, to možemo učiniti kao:
x = y = z = "same" print (x) print (y) print (z)
Drugi program dodjeljuje isti niz svim trima varijablama x, y i z.
Konstante
Konstanta je vrsta varijable čija se vrijednost ne može mijenjati. Korisno je konstante smatrati spremnicima koji sadrže informacije koje se kasnije ne mogu mijenjati.
Konstante možete smatrati torbom za pohranu nekih knjiga koje se ne mogu zamijeniti kad se jednom stave u vreću.
Dodjeljivanje vrijednosti konstanti u Pythonu
U Pythonu se konstante obično deklariraju i dodjeljuju u modulu. Ovdje je modul nova datoteka koja sadrži varijable, funkcije itd. Koja se uvozi u glavnu datoteku. Unutar modula konstante su napisane svim velikim slovima i podvlakama koje razdvajaju riječi.
Primjer 3: Deklariranje i dodjeljivanje vrijednosti konstanti
Stvorite constant.py :
PI = 3.14 GRAVITY = 9.8
Stvorite main.py :
import constant print(constant.PI) print(constant.GRAVITY)
Izlaz
3,14 9,8
U gornjem programu stvaramo datoteku modula constant.py . Zatim konstantnu vrijednost dodjeljujemo PI i GRAVITACIJI. Nakon toga kreiramo datoteku main.py i uvozimo constantmodul. Na kraju ispisujemo konstantnu vrijednost.
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.
