Bài trước: Python căn bản (2): Syntax
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3. Python Variables
3.1 Variables
Variables are containers for storing data values.
Creating variables
Python has no command for declaring a variable.
A variable is created the moment you first assign a value to it.
Example
x = 5
y = "John"
print(x)
print(y)
Variables do not need to be declared with any particular type, and
can even change type after they have been set.
Example
x = 4 #
x is of type int
x = "Sally" # x is now of type str
print(x)
Casting
If you want to specify the data type of a variable, this can be
done with casting.
Example
x = str(3) # x will be '3'
y = int(3) # y will be 3
z = float(3) # z will be 3.0
Get the type
You can get the data type of a variable with the type() function.
Example
x = 5
y = "John"
print(type(x))
print(type(y))
Single or Double Quotes?
String variables can be declared either by using single or double
quotes:
Example
x = "John"
# is the same as
x = 'John'
print(x)
Case-Sensitive
Variable names are case-sensitive.
Example
This will create two variables:
a = 4
A = "Sally"
#A will not overwrite a
print(a)
print(A)
3.2 Variable Name
A variable can have a short name (like x and y) or a more
descriptive name (age, carname, total_volume). Rules for Python variables:
- A variable name must start with a letter or the underscore
character
- A variable name cannot start with a number
- A variable name can only contain alpha-numeric characters and
underscores (A-z, 0-9, and _ )
- Variable names are case-sensitive (age, Age and AGE are three
different variables)
- A variable name cannot be any of the Python keywords.
Example
Legal variable names:
myvar = "John"
my_var = "John"
_my_var = "John"
myVar = "John"
MYVAR = "John"
myvar2 = "John"
Example
Illegal variable names:
2myvar = "John"
my-var = "John"
my var = "John"
Multi Words Variable Names
Variable names with more than one word can be difficult to read.
There are several techniques you can use to make them more
readable:
Camel Case
Each word, except the first, starts with a capital letter:
Example
myVariableName = "John"
Pascal Case
Each word starts with a capital letter:
Example
MyVariableName = "John"
Snake Case
Each word is separated by an underscore character:
Example
my_variable_name = "John"
3.3 Input data from the keyboard
The input() function is the simplest way to get keyboard data from the user in Python.
When called, it asks the user for input with a prompt that you specify, and it waits for the user to type a response and press the Enter key.
Example
name = input("Your name: ")
print(name)
3.4 Exercise
1. What is a correct way to declare a Python variable?
A. var x = 5
B. #x = 5
C. x = 5
D. $x = 5
2. True or False:
You can declare string variables with single or double quotes.
x = "John"
# is the same as
x = 'John'
A. True
B. False
3. True or False:
Variable names are not case-sensitive.
a = 5
# is the same as
A = 5
A. True
B. False
4. Which is NOT a legal variable name?
A. my-var = 20
B. my_var = 20
C. Myvar = 20
D. _myvar = 20
5. Create a variable named carname and assign the value Volvo to
it. Which is correct?
A. carname = Volvo
B. “carname” = “Volvo”
C. carname = “Volvo”
D. “carname” = Volvo
6. Create a variable named x and assign the value 50 to it. Which
is correct?
A. x = “50”
B. x = 50
C. “x” = “50”
D. “x” = 50
7. Creating two
variables to store your age and your
full name. Print values of two
variables out screen. Hints: variables named myAge, myFullname.
Expected output:
11 Nguyen Van Teo
8. Using input()
function to get data from the keyboard. Example:
myAge = input(“So tuoi cua ban la: “)
Write the program to get the: full name, age, phone number,
address from the keyboard, then print out the screen.
Expected output:
Ho ten cua ban la: Nguyen Van Teo
Tuoi cua ban la:10
So dien thoai cua ban la:0988765432
Dia giao hang la:12 Bui Thi Xuan - Dalat
Thong tin cua ban:
Nguyen Van Teo 10 0988765432 12 Bui Thi Xuan - Dalat
----- Cập nhật 16/9/2024 -----
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Bài sau: Python căn bản (4): Variables (cont)
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