Python3 First Steps in Programming

In the previous tutorials, we have learned some basic Python3 syntax knowledge. Now let’s try some examples.

Print a string:

Example

print("Hello, world!")

Output:

Hello, world!

Output a variable value:

Example

i = 256*256
print('The value of i is:', i)

Output:

The value of i is: 65536

Define variables and perform simple mathematical operations:

Example

x = 3
y = 2
z = x + y
print(z)

Output:

5

Define a list and print its elements:

Example

my_list = ['google', 'runoob', 'taobao']
print(my_list[0]) # Output "google"
print(my_list[1]) # Output "runoob"
print(my_list[2]) # Output "taobao"

Output:

google
runoob
taobao

Use a for loop to print numbers 0 to 4:

Example

for i in range(5):
    print(i)

Output:

0
1
2
3
4

Output different results based on conditions:

Example

x = 6
if x > 10:
    print("x is greater than 10")
else:
    print("x is less than or equal to 10")

Output:

x is less than or equal to 10

Next, let’s try to write a Fibonacci sequence.

The Fibonacci sequence is a classic mathematical problem where each number is the sum of the two preceding ones.

Example (Python 3.0+)

#!/usr/bin/python3
 
# Fibonacci series: Fibonacci sequence
# The sum of two elements determines the next number
a, b = 0, 1
while b < 10:
    print(b)
    a, b = b, a+b

The code a, b = b, a+b works by first evaluating the right-hand expression and then simultaneously assigning to the left-hand side, which is equivalent to:

n=b
m=a+b
a=n
b=m

Executing the above program produces the following output:

1
1
2
3
5
8

This example introduces several new features.

The first line contains a compound assignment: variables a and b simultaneously get the new values 0 and 1. The last line uses the same method again. As you can see, the right-hand expression is evaluated before the assignment changes take effect. The evaluation order of the right-hand expression is from left to right.

You can also use a for loop to implement it:

Example

n = 10
a, b = 0, 1
for i in range(n):
    print(b)
    a, b = b, a + b

end Keyword

The end keyword can be used to output results on the same line or add different characters at the end of the output, as shown in the example below:

Example (Python 3.0+)

#!/usr/bin/python3
 
# Fibonacci series: Fibonacci sequence
# The sum of two elements determines the next number
a, b = 0, 1
while b < 1000:
    print(b, end=',')
    a, b = b, a+b

Executing the above program produces the following output:

1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,