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Can you tell what the code below does?

continents = ['Africa', 'Antarctica', 'Asia', 'Australia/Oceania', 'Europe', 'North America', 'South America']
print(continents[0])
print(continents[1])
print(continents[2])
print(continents[3])
print(continents[4])
print(continents[5])
print(continents[6])

Yes! It prints out the continents of the world! You may have noticed that this is a situation where we want to do some action on each item in a list (in this case, that is to print out the continent name). But what if we have a list containing all the countries of the world and wanted to print out each country? Do we need to painstakingly write a hundred of print statements? Or you started thinking, Is there a way that allows us to go through the list and execute the same action multiple times?

Yes! Python loops allows us to:

  • Iterate through the list and perform an action to each element of the list
  • Execute a block of code multiple times

Syntax

For loop

The for loop has the ff. syntax:

for <item> in <list>:
    <the block of actions to be executed for each item>

Say no to repeated lines of code! Let's rewrite the code above using a for loop!

continents = ['Africa', 'Antarctica', 'Asia', 'Australia/Oceania', 'Europe', 'North America', 'South America']
for continent in continents:
    print(continent)

# Will print out
# Africa
# Antarctica
# Asia
# Australia/Oceania
# Europe
# North America
# South America

While loop

The while loop has the ff. syntax:

while <expression>:
    <statement/s>

The while loop allows us to repeatedly execute a block of code as long as the expression evaluates to True. Let's do a New Year countdown!

count = 10
while count > 0:
   print(count)
   count = count - 1
print('Happy New Year!')

Takeaways

  • We can use break, continue and pass as control statements in the loop. Google it!

!> Beware of Infinite loop! Use while loops with caution because if the expression did NOT resolve to a False the loooooooooooooop will go on forever just like below.

is_hungry = True
while is_hungry:
    print('Vikings here I come!')

Challenge

During closing, Aling Nena counts from her vault the day's total income and also the total amount of all her paper bills.

Help Aling Nena count her total income and total amount of her paper bills from a list of cash money and using a loop!

Example:

>> Hi Aling Nena! Your total income for the day is 2947.
>> The total amount of your paper bills is 2920.

!> Please use below template

loops

challenge_partial

Put your thinking cap on!

  • What are the specific characteristics of the for and while loop?
  • What is the effect of break, continue and pass control statements in a loop?