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Python Loops Tutorial
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Python Loops Tutorial

Python Loops Tutorial

1. The For Loop
The First For LoopIterating with range() FunctionCounting with LoopsLoop Control StatementsThe Else Statement in a for LoopThe enumerate() Function
2. The while Loop
The First while LoopInfinite LoopUsing Condition Statements in a while LoopLoop Control Statements in a while LoopThe else Statement in a while LoopChoosing Between for and while Loops in Python
3. Nested Loops
Nested for LoopNested while Loopif/else in a Nested Loopbreak/continue in a Nested Loop
4. List and Dictionary Comprehensions
List ComprehensionsList Comprehansions with ConditionsDictionary ComprehensionsDictionary Comprehension with Condition

book
Loop Control Statements

When working with loops, the break and continue statements help manage the flow of iteration:

  • break: exits the loop prematurely when a condition is met;
  • continue: skips the current iteration and moves to the next one, allowing selective execution;
  • pass: is a placeholder that does nothing when executed.

Using break Keyword

Imagine searching for a specific city in a list. If we want to stop searching as soon as we find the city "Barcelona", we can use the break statement.


              
123456789

            
travel_list = ['Monako', 'Luxemburg', 'Liverpool', 'Barcelona', 'Munchen']

# Searching for a specific city
for city in travel_list:
    if city == 'Barcelona':
        print('Found Barcelona!')
        break
    else:
        print(city, 'is not Barcelona')
copy
  • The loop iterates through each city in the travel_list;
  • When it encounters "Barcelona", the break statement is executed, and the loop stops immediately;
  • Cities after "Barcelona" (like "Munchen") are not processed.

Using continue Keyword

Let's now count the cities in the travel_list that have names shorter than 8 characters while skipping others.


              
12345678910

            
travel_list = ['Monako', 'Luxemburg', 'Liverpool', 'Barcelona', 'Munchen']

short_name_count = 0

for city in travel_list:
    if len(city) >= 8:
        continue  # Skip cities with names 8 or more characters long
    short_name_count += 1

print('Number of cities with names shorter than 8 characters:',  short_name_count)
copy
  • The loop iterates through each city in the travel_list;
  • If the length of the city's name is 8 characters or more, the if condition evaluates to True, and the continue statement is executed. This skips the rest of the code for that iteration;
  • For cities with names shorter than 8 characters, the counter short_name_count is incremented by 1;
  • After the loop finishes, the final count is printed, showing how many cities have names shorter than 8 characters.

The pass Keyword

The pass statement in Python is a placeholder that does nothing when executed. It's often used as a temporary placeholder for code you plan to write later, allowing the program to run without errors. Later, you can replace pass with actual logic.


              
12345678

            
travel_list = ['Monaco', 'Luxembourg', 'Liverpool', 'Barcelona', 'Munich']
already_visited = ['Barcelona', 'Monaco']

for city in travel_list:
    if city in already_visited:
        pass
    else:
        print('Going to visit', city)
copy
Opgave

Swipe to start coding

You're planning your next adventure and want to prioritize visa-free travel to make the journey smoother. To keep things manageable, you decide to limit your list to only 10 destinations.

  • Iterate through the countries list. Skip the countries that require a visa.
  • Add only visa-free countries to travel_list.
  • Stop adding once travel_list contains 10 countries.

Løsning

Switch to desktopSkift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder
Var alt klart?

Hvordan kan vi forbedre det?

Tak for dine kommentarer!

Sektion 1. Kapitel 4
toggle bottom row

book
Loop Control Statements

When working with loops, the break and continue statements help manage the flow of iteration:

  • break: exits the loop prematurely when a condition is met;
  • continue: skips the current iteration and moves to the next one, allowing selective execution;
  • pass: is a placeholder that does nothing when executed.

Using break Keyword

Imagine searching for a specific city in a list. If we want to stop searching as soon as we find the city "Barcelona", we can use the break statement.


              
123456789

            
travel_list = ['Monako', 'Luxemburg', 'Liverpool', 'Barcelona', 'Munchen']

# Searching for a specific city
for city in travel_list:
    if city == 'Barcelona':
        print('Found Barcelona!')
        break
    else:
        print(city, 'is not Barcelona')
copy
  • The loop iterates through each city in the travel_list;
  • When it encounters "Barcelona", the break statement is executed, and the loop stops immediately;
  • Cities after "Barcelona" (like "Munchen") are not processed.

Using continue Keyword

Let's now count the cities in the travel_list that have names shorter than 8 characters while skipping others.


              
12345678910

            
travel_list = ['Monako', 'Luxemburg', 'Liverpool', 'Barcelona', 'Munchen']

short_name_count = 0

for city in travel_list:
    if len(city) >= 8:
        continue  # Skip cities with names 8 or more characters long
    short_name_count += 1

print('Number of cities with names shorter than 8 characters:',  short_name_count)
copy
  • The loop iterates through each city in the travel_list;
  • If the length of the city's name is 8 characters or more, the if condition evaluates to True, and the continue statement is executed. This skips the rest of the code for that iteration;
  • For cities with names shorter than 8 characters, the counter short_name_count is incremented by 1;
  • After the loop finishes, the final count is printed, showing how many cities have names shorter than 8 characters.

The pass Keyword

The pass statement in Python is a placeholder that does nothing when executed. It's often used as a temporary placeholder for code you plan to write later, allowing the program to run without errors. Later, you can replace pass with actual logic.


              
12345678

            
travel_list = ['Monaco', 'Luxembourg', 'Liverpool', 'Barcelona', 'Munich']
already_visited = ['Barcelona', 'Monaco']

for city in travel_list:
    if city in already_visited:
        pass
    else:
        print('Going to visit', city)
copy
Opgave

Swipe to start coding

You're planning your next adventure and want to prioritize visa-free travel to make the journey smoother. To keep things manageable, you decide to limit your list to only 10 destinations.

  • Iterate through the countries list. Skip the countries that require a visa.
  • Add only visa-free countries to travel_list.
  • Stop adding once travel_list contains 10 countries.

Løsning

Switch to desktopSkift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder
Var alt klart?

Hvordan kan vi forbedre det?

Tak for dine kommentarer!

Sektion 1. Kapitel 4
Switch to desktopSkift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder
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