I denne vejledning lærer du om Python-variabler, konstanter, bogstaver og deres brugssager.
Video: Python-variabler og print ()
Python-variabler
En variabel er et navngivet sted, der bruges til at gemme data i hukommelsen. Det er nyttigt at tænke på variabler som en container, der indeholder data, der kan ændres senere i programmet. For eksempel,
number = 10
Her har vi oprettet en variabel med navnet nummer. Vi har tildelt variablen værdien 10.
Du kan tænke på variabler som en pose til at gemme bøger i den, og den bog kan udskiftes når som helst.
number = 10 number = 1.1
Oprindeligt var antallet af tal 10. Senere blev det ændret til 1.1.
Bemærk : I Python tildeler vi faktisk ikke værdier til variablerne. I stedet giver Python objektets (værdi) reference til variablen.
Tildeling af værdier til variabler i Python
Som du kan se fra ovenstående eksempel, kan du bruge tildelingsoperatøren =til at tildele en værdi til en variabel.
Eksempel 1: Erklæring og tildeling af værdi til en variabel
website = "apple.com" print(website)
Produktion
apple.com
I ovenstående program tildelte vi en værdi apple.com til den variable webside. Derefter udskrev vi den værdi, der er tildelt webstedet, dvs. apple.com
Bemærk : Python er et typeafledt sprog, så du behøver ikke eksplicit at definere variabeltypen. Det ved automatisk, at apple.com er en streng og erklærer webstedsvariablen som en streng.
Eksempel 2: Ændring af værdien af en variabel
website = "apple.com" print(website) # assigning a new value to website website = "programiz.com" print(website)
Produktion
apple.com programiz.com
I ovenstående program har vi oprindeligt tildelt apple.com til webstedsvariablen. Derefter ændres værdien til programiz.com.
Eksempel 3: Tildeling af flere værdier til flere variabler
a, b, c = 5, 3.2, "Hello" print (a) print (b) print (c)
Hvis vi vil tildele den samme værdi til flere variabler på én gang, kan vi gøre dette som:
x = y = z = "same" print (x) print (y) print (z)
Det andet program tildeler den samme streng til alle de tre variabler x, y og z.
Konstanter
En konstant er en type variabel, hvis værdi ikke kan ændres. Det er nyttigt at tænke på konstanter som containere, der indeholder information, som ikke kan ændres senere.
Du kan tænke på konstanter som en pose til opbevaring af nogle bøger, som ikke kan udskiftes, når de først er placeret inde i posen.
Tildeling af værdi til konstant i Python
I Python bliver konstanter normalt erklæret og tildelt i et modul. Her er modulet en ny fil, der indeholder variabler, funktioner osv., Som importeres til hovedfilen. Inde i modulet er konstanter skrevet med alle store bogstaver og understreger, der adskiller ordene.
Eksempel 3: Erklæring og tildeling af værdi til en konstant
Opret en konstant.py :
PI = 3.14 GRAVITY = 9.8
Opret en main.py :
import constant print(constant.PI) print(constant.GRAVITY)
Produktion
3,14 9,8
I ovenstående program opretter vi en constant.py- modulfil. Derefter tildeler vi den konstante værdi til PI og GRAVITY. Derefter opretter vi en main.py- fil og importerer constantmodulet. Endelig udskriver vi den konstante værdi.
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.
