Bài trước: Python căn bản (3): Variables
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4. Python Variables
(cont)
4.1 Assign Multiple Values
Many Values to Multiple Variables
Python allows you to assign values to multiple variables in one
line:
Example
x, y, z = "Orange", "Banana", "Cherry"
print(x)
print(y)
print(z)
Note: Make sure the number of variables matches the number of
values, or else you will get an error.
One Value to Multiple Variables
And you can assign the same value to multiple variables in one
line:
Example
x = y = z = "Orange"
print(x)
print(y)
print(z)
Unpack a Collection
If you have a collection of values in a list, tuple etc. Python
allows you to extract the values into variables. This is called unpacking.
Example
Unpack a list:
fruits = ["apple", "banana", "cherry"]
x, y, z = fruits
print(x)
print(y)
print(z)
4.2 Output Variables
The Python print() function is often used to output variables.
Example
x = "Python is awesome"
print(x)
In the print() function,
you output multiple variables, separated by a comma:
Example
x = "Python"
y = "is"
z = "awesome"
print(x, y, z)
You can also use the +
operator to output multiple variables:
Example
x = "Python "
y = "is "
z = "awesome"
print(x + y + z)
Notice the space character
after "Python " and "is ", without them the result would be
"Pythonisawesome".
For numbers, the +
character works as a mathematical operator:
Example
x = 5
y = 10
print(x + y)
In the print() function,
when you try to combine a string and a number with the + operator, Python will
give you an error:
Example
x = 5
y = "John"
print(x + y)
The best way to output
multiple variables in the print() function is to separate them with commas,
which even support different data types:
Example
x = 5
y = "John"
print(x, y)
4.3 Global Variables
Variables that are created
outside of a function (as in all of the examples in the previous pages) are
known as global variables.
Global variables can be
used by everyone, both inside of functions and outside.
Example
Create a variable outside of a function, and use it inside the
function
x = "awesome"
def myfunc():
print("Python is " + x)
myfunc()
If you create a variable
with the same name inside a function, this variable will be local, and can only
be used inside the function. The global variable with the same name will remain
as it was, global and with the original value.
Example
Create a variable inside a function, with the same name as the
global variable
x = "awesome"
def myfunc():
x = "fantastic"
print("Python is " + x)
myfunc()
print("Python is " + x)
The global Keyword
Normally, when you create
a variable inside a function, that variable is local, and can only be used
inside that function.
To create a global variable inside a function, you can use the
global keyword.
Example
If you use the global keyword, the variable belongs to the global
scope:
def myfunc():
global x
x = "fantastic"
myfunc()
print("Python is " + x)
Also, use the global
keyword if you want to change a global variable inside a function.
Example
To change the value of a global variable inside a function, refer
to the variable by using the global keyword:
x = "awesome"
def myfunc():
global x
x = "fantastic"
myfunc()
print("Python is " + x)
4.4 Exercise
1. What is the correct syntax to add the value 'Hello World', to 3
values in one statement?
A. x, y, z = 'Hello World'
B. x = y = z = 'Hello World'
C. x|y|z = 'Hello World'
D. 'x' = 'y' = 'z' = 'Hello World'
2. What is the correct syntax to assign values to multiple
variables in one line?
A. x, y, z = "Orange", "Banana", "Cherry"
B. x = y = z = "Orange", "Banana",
"Cherry"
C. x|y|z = "Orange", "Banana", "Cherry"
D. 'x' = 'y' = 'z' = "Orange", "Banana",
"Cherry"
3. Consider the following code:
fruits = ['apple',
'banana', 'cherry']
a, b, c = fruits
print(a)
What will be the result of a?
A. apple
B. banana
C. cherry
D. True
4. Consider the following code:
print('Hello', 'World')
What will be the printed result?
A. Hello, World
B. Hello World
C. HelloWorld
D. 'Hello', 'World'
5. Consider the following code:
a = 'Hello'
b = 'World'
print(a + b)
What will be the printed result?
A. a + b
B. Hello World
C. HelloWorld
D. 'Hello''World'
6. Consider the following code:
a = 4
b = 5
print(a + b)
What will be the printed result?
A. 45
B. 9
C. 4 + 5
D. Error
7. Consider the following code:
x = 'awesome'
def myfunc():
x = 'fantastic'
myfunc()
print('Python is ' + x)
What will be the printed result?
A. Python is awesome
B. Python is fantastic
C. Python is x
D. Python is + x
8. Insert the correct keyword to make the variable x belong to the
global scope.
______x
x = "fantastic"
A. global variable
B. global
C. Global
D. “Global”
9. Consider the following code:
x = 'awesome'
def myfunc():
global x
x = 'fantastic'
myfunc()
print('Python is ' + x)
What will be the printed result?
A. Python is awesome
B. Python is fantastic
C. Python is True
D. Python is False
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