For loop

With this function we can execute a set of statements. It is used when you need to check in a condition each iteration, or to repeat a block of code.

Example:

countries = ["Spain", "France", "Italy", "Greece"]
for country in countries:
        print(country)

Output: As a result are displayed one by one the items.

Spain
France
Italy
Greece

Break statement

With this statement we can stop the loop before finish.

Example:

countries = ["Spain", "France", "Italy", "Greece"]
for  x in countries:
        print(x)
        if x == "Italy":
            break

Output: You can see here that in this time we cannot see “Greece” like in the other example, because the function exit the loop when comply the condition.

Spain
France
Italy

Continue statement

This one is similar to the other, the different is that we can stop the current iteration of the loop and continue with the next.

Example:

countries = ["Spain", "France", "Italy", "Greece"]
for  x in countries:
    if x == "France":
        continue
    print(x)

Output: We can see that “France” is not present.

Spain
Italy
Greece

Looping through a string

With this function we can print each letter of a string in a single line after the loop.

Example:

for x in "France":
  print(x)

Output:

F
r
a
n
c
e

There is only 1 letter in every line.

The range() function

This function returns a sequence of numbers, starting from 0 by default, and increments by 1 (by default), and ends at a specified number.

Syntax

range(start, stop, step)

• start = Optional.Default is 0.
• stop = Required. An integer number specifying at which position to stop (not included).
• step = Optional. Default is 1.

Example:

for x in range(6):
  print(x)

Output: We can see here that for default is counting one by one, start in 0 and finished in 5 because was the only value that we define.

0
1
2
3
4
5

This could be a little different if we define every value by adding two additional parameter. I mean, start and step. In this example i will define ever value so it will star in the number 5, it will sop in the number 30 and will be counting from five to five:

for x in range(5,30,5):
  print(x)

Output:

5
10
15
20
25

Else in For Loop

The else keyword in a for loop specifies a block of code to be executed when the loop is finished.

Example - Print all numbers from 0 to 4, and print a message when the loop ends:

for x in range(4):
  print(x)
else:
  print("Time to start!")

Output:

0
1
2
3
Time to start!

Note: The else block will NOT be executed if the loop is stopped by a break statement.

Example - Break the loop when x is “Three”:

numbers =  ["One", "Two", "Three", "Four"]
for x in numbers:
     if x == "Three":
       break
     print(x)
else:
     print("Hello everyone!")

Output: You can see what happens with the else block, as a result is not executed.

One
Two

The pass statement

• For loops cannot be empty, but if you for some reason have a for loop with no content, use the pass statement to avoid getting an error.
• The pass statement is a null operation; nothing happens when it is executed.
• The pass is also useful in places where your code will eventually go, but has not been written yet.

Example:

numbers =  ["One", "Two", "Three", "Four"]
for x in numbers:
     if x == "Three":
      pass
     print(x)
else:
     print("Hello everyone!")

Output: But is don’t use the pass statement, the code will have an error and don’t will be executed.

One
Two
Three
Four
Hello everyone!

Nested Loops

A nested loop is a loop inside a loop.

Example:

color = ["White", "Black", "Brown"]
animal = ["dog", "cat", "mouse"]
for x in color:
  for y in animal:
    print(x, y) 

Output:

White dog
White cat
White mouse
Black dog
Black cat
Black mouse
Brown dog
Brown cat
Brown mouse