---
## Discussion: A Small list
This situation isn’t so bad…
```
visible_colors = ["red", "orange", "yellow", "green", "blue", "violet"]
print(visible_colors[0])
print(visible_colors[1])
print(visible_colors[2])
print(visible_colors[3])
print(visible_colors[4])
print(visible_colors[5])
```
But, what would we do if there were 1,000 items in the list to print?
---
## The "For" Loop {.separator-subhead}
---
## The `for` Loop
The `for` loop always follows this form:
```
for item in collection:
# Do something with item
```
For example:
```
visible_colors = ["red", "orange", "yellow", "green", "blue", "violet"]
for each_color in visible_colors:
print(each_color)
```
---
## Knowledge Check: What Will This Code Do?
Think about what the code will do before you actually run it.
---
## Writing a Loop
Let's write a loop to print names of guests.
First, we need a list.
- Create a local `.py` file named `my_loop.py`.
- Make your list: Declare a variable `my_list` and assign it to a list containing the names of at least five people.
---
## Write a Loop — Make the Loop
Now we'll add the loop.
- Skip a line and write the first line of your for loop.
- For the variable that holds each item, give it a name that reflects what the item is (e.g., name of person).
- Inside your loop, add the code to print "Hello," plus the name.
```
"Hello, Felicia!"
"Hello, Srinivas!"
```
---
## Write a Loop Greeting Your Guest List
Our guests are definitely VIPs! Let's give them a lavish two-line greeting.
- Inside your loop, add the code to print another sentence of greeting:
```
"Hello, Srinivas!"
"Welcome to the party!"
```
---
## Where Else Could We Use a Loop?
A loop prints everything in a collection of items.
- `guest_list = ["Fred", "Cho", "Brandi", "Yuna", "Nanda", "Denise"]`
What, besides a list, could we use a loop on?
**Hint**: There are six on this slide!
---
## Looping Strings
Loops are collections of strings and numbers.
Strings are collections of characters!
---
## What About… Looping for a Specific Number of Iterations?
We have:
```
guest_list = ["Fred", "Cho", "Brandi", "Yuna", "Nanda", "Denise"]
for guest in guest_list:
print("Hello, " + guest + "!")
```
The loop runs for every item in the list — the length of the collection. Here, it runs six times.
What if we don't know how long guest_list will be?
Or only want to loop some of it?
---
## Range() {.separator-subhead}
---
## Enter: Range
range(x):
- Automatically generated.
- A list that contains only integers.
- Starts at zero.
- Stops before the number you input.
`range(5) # => [0, 1, 2, 3, 4]`
---
## Looping Over a Range
Let's look at range() in action:
---
## Looping Over a Range
Looping over names here is really just going through the loop four times: At index `0, 1, 2`, and `3`.
We can instead use `range()` to track the index and loop names: `range(4)` is `[0, 1, 2, 3]`.
We can then use `len(names)`, which is 4, as our range.
---
## Using `range()` to Modify Collections
Why would you use `range()` on a list, when you could just loop the list?
We can't do:
```
guest_list = ["Fred", "Cho", "Brandi", "Yuna", "Nanda", "Denise"]
for guest in guest_list:
guest = "A new name"
```
But we can do:
```
guest_list = ["Fred", "Cho", "Brandi", "Yuna", "Nanda", "Denise"]
for guest in range(len(guest_list)):
guest_list[guest] = "A new name"
```
---
## Looping Over a Range
Let’s make this list all uppercase:
---
## Knowledge Check
`my_list = ['mon', 'tue', 'wed', 'thu', 'fri']`
Which of the following lines is correct?
```
for day in range(my_list): # answer A
for day in range(len(my_list)): # answer B
for day in range(my_list.length): # answer C
```
---
## Solo Exercise: Range() (5–10 minutes)
Locally, create a new file called `range_practice.py`.
In it:
- Create a list of colors.
- Using a `for` loop, print out the list.
- Using `range()`, set each item in the list to be the number of characters in the list.
- For example:
```
["red", "green", "blue"]
# =>
[3, 5, 4]
```
---
## Quick Review: `for` Loops and Range
`for` Loops
```
# On a list (a collection of strings) guest_list = ["Fred", "Cho", "Brandi", "Yuna", "Nanda", "Denise"]
for guest in guest_list:
print("Hello, " + guest + "!")
# On a string (a collection of characters)
my_string = "Hello, world!"
for character in my_string:
print(character)
##### Range #####
range(4) # => [0, 1, 2, 3]
# Using Range as an Index Counter
names = ["Flint", "John Cho", "Billy Bones", "Nanda Yuna"]
for each_name in range(4):
print(names[each_name])
```
---
## Quick Review: `for` Loops and Range
```
# OR
for each_name in range(len(names)):
print(names[each_name])
# Using Range to Change a List:
guest_list = ["Fred", "Cho", "Brandi", "Yuna", "Nanda", "Denise"]
for guest in range(len(guest_list)):
guest_list[guest] = "A new name"
```
---
## The “While” Loop {.separator-subhead}
---
## The `while` Loop
What about "While the bread isn't brown, keep cooking"?
Python provides two loop types.
`for`:
- You just learned!
- Loops over collections a finite number of times.
`while`:
- You're about to learn!
- When your loop could run an indeterminate number of times.
- Checks if something is `True` _(the bread isn't brown yet)_ and runs until it's set to `False` _(now the bread is brown, so stop)_.
---
## `while` Loop Syntax
```
# While is True:
# Run some code.
# If you're done, set the to False.
# Otherwise, repeat.
a = 0
while a < 10:
print(a)
a += 1
```
---
## `while` Loop Syntax
---
## `while`: Be Careful!
Don't _ever_ do:
```
a = 0
while a < 10:
print(a)
```
And don't _ever_ do:
```
a = 0
while a < 10:
print(a)
a += 1
```
Your program will run forever!
If your program ever doesn't leave a loop, hit `control-c` (break).
---
## Filling a Glass of Water
Create a new local file, `practicing_while.py`.
In it, we'll create:
- A variable for our current glass content.
- Another variable for the total capacity of the glass.
Let's start with this:
```
glass = 0
glass_capacity = 12
```
Can you start the `while` loop?
---
## Filling a Glass of Water
Add the loop:
```
glass = 0
glass_capacity = 12
while glass < glass_capacity:
glass += 1 # Here is where we add more water.
```
That’s it!
---
## Side Note: `input()`
Let's do something more fun. With a partner, you will write a program that
- Has a user guess a number.
- But first, how do we have users input numbers? Using `input()`.
```
user_name = input("Please enter your name:")
# user_name now has what the user typed.
print(user_name)
```
Erase the code in your `practicing_while.py` file and replace it with the above code.
Run it! What happens? Does it work?
---
## A Guessing Game (5 minutes)
Now, get with a partner! Let's write the game.
Decide who will be the driver and who will be the navigator. Add this to your existing file.
- Set a variable, answer to "5" (yes, a string!).
- Prompt the user for a guess and save it in a new variable, `guess`.
- Create a `while` loop, ending when `guess` is equal to `answer`.
- In the `while` loop, prompt the user for a new `guess`.
- After the `while` loop, print: "You did it!"
Discuss with your partner: Why do we need to make an initial variable before the loop?
---
## A Guessing Game (Solution)
```
answer = "4"
guess = input("Guess what number I'm thinking of (1-10): ")
while guess != answer:
guess = input("Nope, try again: ")
print("You got it!")
```
How'd you do? Questions?
---
## Conclusion {.separator-subhead}
---
## Python Programming: Loops {.separator-subhead}
**Lesson Summary**
Today we explored:
- Loops:
- Common, powerful control structures that let us efficiently deal with repetitive tasks.
- `for` loops:
- Used to iterate a set number of times over a collection (e.g., list, string, or using `range`).
- `range()` uses indices, not duplicates, so it lets you modify the collection.
---
## Python Programming: Loops {.separator-subhead}
**Lesson Summary**
Today we explored:
- `while` loops:
- Run until a condition is False.
- Used when you don't know how many times you need to iterate.
Up Next:
{Add Upcoming Lesson Topics/Pre-Work}
---
## Q&A {.separator-subhead}
---
## Additional Resources {.separator-subhead}
---
## Additional Reading
[Learn Python Programming: Loops Video](https://www.youtube.com/watch?v=JkQ0Xeg8LRI)
[Python: For Loop](https://wiki.python.org/moin/ForLoop)
[Python: Loops](https://www.tutorialspoint.com/python/python_loops.htm)
---
## Exit Tickets {.separator-subhead}
---
---
## Discussion: A Small list
This situation isn’t so bad…
```
visible_colors = ["red", "orange", "yellow", "green", "blue", "violet"]
print(visible_colors[0])
print(visible_colors[1])
print(visible_colors[2])
print(visible_colors[3])
print(visible_colors[4])
print(visible_colors[5])
```
But, what would we do if there were 1,000 items in the list to print?
---
## The "For" Loop {.separator-subhead}
---
## The `for` Loop
The `for` loop always follows this form:
```
for item in collection:
# Do something with item
```
For example:
```
visible_colors = ["red", "orange", "yellow", "green", "blue", "violet"]
for each_color in visible_colors:
print(each_color)
```
---
## Knowledge Check: What Will This Code Do?
Think about what the code will do before you actually run it.
---
## Writing a Loop
Let's write a loop to print names of guests.
First, we need a list.
- Create a local `.py` file named `my_loop.py`.
- Make your list: Declare a variable `my_list` and assign it to a list containing the names of at least five people.
---
## Write a Loop — Make the Loop
Now we'll add the loop.
- Skip a line and write the first line of your for loop.
- For the variable that holds each item, give it a name that reflects what the item is (e.g., name of person).
- Inside your loop, add the code to print "Hello," plus the name.
```
"Hello, Felicia!"
"Hello, Srinivas!"
```
---
## Write a Loop Greeting Your Guest List
Our guests are definitely VIPs! Let's give them a lavish two-line greeting.
- Inside your loop, add the code to print another sentence of greeting:
```
"Hello, Srinivas!"
"Welcome to the party!"
```
---
## Where Else Could We Use a Loop?
A loop prints everything in a collection of items.
- `guest_list = ["Fred", "Cho", "Brandi", "Yuna", "Nanda", "Denise"]`
What, besides a list, could we use a loop on?
**Hint**: There are six on this slide!
---
## Looping Strings
Loops are collections of strings and numbers.
Strings are collections of characters!
---
## What About… Looping for a Specific Number of Iterations?
We have:
```
guest_list = ["Fred", "Cho", "Brandi", "Yuna", "Nanda", "Denise"]
for guest in guest_list:
print("Hello, " + guest + "!")
```
The loop runs for every item in the list — the length of the collection. Here, it runs six times.
What if we don't know how long guest_list will be?
Or only want to loop some of it?
---
## Range() {.separator-subhead}
---
## Enter: Range
range(x):
- Automatically generated.
- A list that contains only integers.
- Starts at zero.
- Stops before the number you input.
`range(5) # => [0, 1, 2, 3, 4]`
---
## Looping Over a Range
Let's look at range() in action:
---
## Looping Over a Range
Looping over names here is really just going through the loop four times: At index `0, 1, 2`, and `3`.
We can instead use `range()` to track the index and loop names: `range(4)` is `[0, 1, 2, 3]`.
We can then use `len(names)`, which is 4, as our range.
---
## Using `range()` to Modify Collections
Why would you use `range()` on a list, when you could just loop the list?
We can't do:
```
guest_list = ["Fred", "Cho", "Brandi", "Yuna", "Nanda", "Denise"]
for guest in guest_list:
guest = "A new name"
```
But we can do:
```
guest_list = ["Fred", "Cho", "Brandi", "Yuna", "Nanda", "Denise"]
for guest in range(len(guest_list)):
guest_list[guest] = "A new name"
```
---
## Looping Over a Range
Let’s make this list all uppercase:
---
## Knowledge Check
`my_list = ['mon', 'tue', 'wed', 'thu', 'fri']`
Which of the following lines is correct?
```
for day in range(my_list): # answer A
for day in range(len(my_list)): # answer B
for day in range(my_list.length): # answer C
```
---
## Solo Exercise: Range() (5–10 minutes)
Locally, create a new file called `range_practice.py`.
In it:
- Create a list of colors.
- Using a `for` loop, print out the list.
- Using `range()`, set each item in the list to be the number of characters in the list.
- For example:
```
["red", "green", "blue"]
# =>
[3, 5, 4]
```
---
## Quick Review: `for` Loops and Range
`for` Loops
```
# On a list (a collection of strings) guest_list = ["Fred", "Cho", "Brandi", "Yuna", "Nanda", "Denise"]
for guest in guest_list:
print("Hello, " + guest + "!")
# On a string (a collection of characters)
my_string = "Hello, world!"
for character in my_string:
print(character)
##### Range #####
range(4) # => [0, 1, 2, 3]
# Using Range as an Index Counter
names = ["Flint", "John Cho", "Billy Bones", "Nanda Yuna"]
for each_name in range(4):
print(names[each_name])
```
---
## Quick Review: `for` Loops and Range
```
# OR
for each_name in range(len(names)):
print(names[each_name])
# Using Range to Change a List:
guest_list = ["Fred", "Cho", "Brandi", "Yuna", "Nanda", "Denise"]
for guest in range(len(guest_list)):
guest_list[guest] = "A new name"
```
---
## The “While” Loop {.separator-subhead}
---
## The `while` Loop
What about "While the bread isn't brown, keep cooking"?
Python provides two loop types.
`for`:
- You just learned!
- Loops over collections a finite number of times.
`while`:
- You're about to learn!
- When your loop could run an indeterminate number of times.
- Checks if something is `True` _(the bread isn't brown yet)_ and runs until it's set to `False` _(now the bread is brown, so stop)_.
---
## `while` Loop Syntax
```
# While 
---
## `while`: Be Careful!
Don't _ever_ do:
```
a = 0
while a < 10:
print(a)
```
And don't _ever_ do:
```
a = 0
while a < 10:
print(a)
a += 1
```
Your program will run forever!
If your program ever doesn't leave a loop, hit `control-c` (break).
---
## Filling a Glass of Water
Create a new local file, `practicing_while.py`.
In it, we'll create:
- A variable for our current glass content.
- Another variable for the total capacity of the glass.
Let's start with this:
```
glass = 0
glass_capacity = 12
```
Can you start the `while` loop?
---
## Filling a Glass of Water
Add the loop:
```
glass = 0
glass_capacity = 12
while glass < glass_capacity:
glass += 1 # Here is where we add more water.
```
That’s it!
---
## Side Note: `input()`
Let's do something more fun. With a partner, you will write a program that
- Has a user guess a number.
- But first, how do we have users input numbers? Using `input()`.
```
user_name = input("Please enter your name:")
# user_name now has what the user typed.
print(user_name)
```
Erase the code in your `practicing_while.py` file and replace it with the above code.
Run it! What happens? Does it work?
---
## A Guessing Game (5 minutes)
Now, get with a partner! Let's write the game.
Decide who will be the driver and who will be the navigator. Add this to your existing file.
- Set a variable, answer to "5" (yes, a string!).
- Prompt the user for a guess and save it in a new variable, `guess`.
- Create a `while` loop, ending when `guess` is equal to `answer`.
- In the `while` loop, prompt the user for a new `guess`.
- After the `while` loop, print: "You did it!"
Discuss with your partner: Why do we need to make an initial variable before the loop?
---
## A Guessing Game (Solution)
```
answer = "4"
guess = input("Guess what number I'm thinking of (1-10): ")
while guess != answer:
guess = input("Nope, try again: ")
print("You got it!")
```
How'd you do? Questions?
---
## Conclusion {.separator-subhead}
---
## Python Programming: Loops {.separator-subhead}
**Lesson Summary**
Today we explored:
- Loops:
- Common, powerful control structures that let us efficiently deal with repetitive tasks.
- `for` loops:
- Used to iterate a set number of times over a collection (e.g., list, string, or using `range`).
- `range()` uses indices, not duplicates, so it lets you modify the collection.
---
## Python Programming: Loops {.separator-subhead}
**Lesson Summary**
Today we explored:
- `while` loops:
- Run until a condition is False.
- Used when you don't know how many times you need to iterate.
Up Next:
{Add Upcoming Lesson Topics/Pre-Work}
---
## Q&A {.separator-subhead}
---
## Additional Resources {.separator-subhead}
---
## Additional Reading
[Learn Python Programming: Loops Video](https://www.youtube.com/watch?v=JkQ0Xeg8LRI)
[Python: For Loop](https://wiki.python.org/moin/ForLoop)
[Python: Loops](https://www.tutorialspoint.com/python/python_loops.htm)
---
## Exit Tickets {.separator-subhead}
---