Introduction to Coding and Data Analysis for Scientists

Week 3: Loops

Today’s Lecture

Lecture 3: Loops
- Recap: Accessing Noteable
- Recap: If Statements
- For Loops
- While Loops
- Practical

Recap: Accessing Noteable

Open Blackboard
Go to Introduction to Coding and Data Analysis for Scientists 2025
Click Unit Information and Resources
Open Noteable
- Make sure Jupyter Classic (Legacy) is selected.
- Click Start
Click +GitRepo
Paste into Git Repository URL: git@github.com:TomMaullin/SCIF10002-2025.git
Press clone

Welcome page for the unit on Blackboard

Important: Assessed Coursework 1

The first assignment will be released this week!
- Released Wednesday 8th October at 12:00PM
- Due Wednesday 22nd October at 12:00PM
This is assessed (15% of your grade!)
Submission is via Noteable
You can submit as many times as you like up until the submission date

Noteable Submission

Download using the Assignments tab on noteable
Press Fetch and click on the assignment
Fill your answers in and Validate
Once done, save your answers and Submit
Feedback will be available when you see the (view feedback) option

Recap: If Statements

Last week, we looked at the if statement
if statements allow us run code only when a specific condition is True
We can add elif and else statements to give us finer control over when code is executed
- An elif runs if it’s Boolean is True and all previous clauses (ifs and elifs) did not execute
- An else runs if all other clauses did not execute
Today, we will look at another feature of Python that gives us finer control over our code - loops

Motivation

Suppose we want to do a very repetitive computation
For instance, suppose we want to print the square of each item in this list

We could just write something like this…

Motivation

But it would be nice to be able to do this automatically!
This is what loops do!

Iterable Objects

An iterable object is an object which contains lots of elements that we could list one by one
We’ve already seen an example - the list
Other examples include:
- Tuples - like lists but use round brackets and can’t be changed
- Dictionaries - records “keys” and “values” so that we can look up data using labels of our choosing
- A range object - a python object that represents a sequence of numbers, saved in a useful, memory-efficient way
A for loop performs an operation on each element in an iterable object

For Loops

A for loop lets you run code for every element in an iterable object
Let’s look at an example:

Translation:

“For every number in the list, print that number”

While Loops

A while loop lets you run code repeatedly so long as a Boolean statement is True

Let’s compare this to an if statement - An if statement executes once if the Boolean is True - An while loop executes repeatedly until the Boolean is False

Practical

We now move over to Python
Please open week_03_home.ipynb
For the rest of today, you must work through a Python notebook
You have a choice of one of three options

--- title: Introduction to Coding and Data Analysis for Scientists jupyter: python3 --- ## Week 3: Loops ## Today's Lecture - Lecture 3: Loops - Recap: Accessing Noteable - Recap: If Statements - For Loops - While Loops - Practical ## Recap: Accessing Noteable - Open Blackboard - Go to `Introduction to Coding and Data Analysis for Scientists 2025` - Click `Unit Information and Resources` - Open Noteable - Make sure `Jupyter Classic (Legacy)` is selected. - Click Start - Click `+GitRepo` - Paste into Git Repository URL: `git@github.com:TomMaullin/SCIF10002-2025.git` - Press clone <img src="./images/noteable2.png" alt="Welcome page for the unit on Blackboard" style="display:block;margin-left:auto;margin-right:auto;width:20%"/> ## Important: Assessed Coursework 1 - The first assignment will be released this week! - Released `Wednesday 8th October` at `12:00PM` - Due `Wednesday 22nd October` at `12:00PM` - This is assessed (`15%` of your grade!) - Submission is via `Noteable` - You can submit as many times as you like up until the submission date ## Noteable Submission - Download using the Assignments tab on `noteable` - Press `Fetch` and click on the assignment - Fill your answers in and `Validate` - Once done, save your answers and `Submit` - Feedback will be available when you see the `(view feedback)` option ## Recap: If Statements - Last week, we looked at the `if` statement - `if` statements allow us run code only when a specific condition is `True` - We can add `elif` and `else` statements to give us finer control over when code is executed - An `elif` runs if it’s Boolean is True and all previous clauses (`if`s and `elif`s) did not execute - An `else` runs if all other clauses did not execute - Today, we will look at another feature of Python that gives us finer control over our code - loops ```{pyodide} #| slideshow: {slide_type: fragment} number = 5 if number > 0: print("Positive number") elif number == 0: print("Zero") else: print("Negative number") ``` ## Motivation - Suppose we want to do a very repetitive computation - For instance, suppose we want to `print` the square of each item in this list ```{pyodide} #| slideshow: {slide_type: fragment} my_list = [1,5,8,3,2,2,4] ``` - We could just write something like this... ```{pyodide} #| slideshow: {slide_type: fragment} number_squared = my_list[0]**2 print(number_squared) number_squared = my_list[1]**2 print(number_squared) number_squared = my_list[2]**2 print(number_squared) number_squared = my_list[3]**2 print(number_squared) number_squared = my_list[4]**2 print(number_squared) number_squared = my_list[5]**2 print(number_squared) number_squared = my_list[6]**2 print(number_squared) ``` ## Motivation - But it would be nice to be able to do this automatically! - This is what loops do! ```{pyodide} #| slideshow: {slide_type: fragment} # For Loop for num in my_list: number_squared = num ** 2 print(number_squared) print('--------------') # While Loop i=0 while i < len(my_list): number_squared = my_list[i] ** 2 print(number_squared) i += 1 ``` ## Iterable Objects - An iterable object is an object which contains lots of elements that we could list one by one - We've already seen an example - the `list` - Other examples include: - Tuples - like lists but use round brackets and can't be changed - Dictionaries - records "keys" and "values" so that we can look up data using labels of our choosing - A `range` object - a python object that represents a sequence of numbers, saved in a useful, memory-efficient way - A `for` loop performs an operation on each element in an iterable object ```{pyodide} #| slideshow: {slide_type: fragment} # Example Tuple my_tuple = (1,5,2,4) # Example dict my_dict = {"Alice": 25, "Bob": 30, "Charlie": 22} print(my_dict["Bob"]) # Example range my_range = range(10) ``` ## For Loops - A `for` loop lets you run code for every element in an iterable object - Let's look at an example: ```{pyodide} #| slideshow: {slide_type: fragment} numbers = [1, 2, 3, 4, 5] for n in numbers: print(n) ``` Translation: > *"For every number in the list, print that number"* ## While Loops - A `while` loop lets you run code repeatedly so long as a Boolean statement is `True` ```{pyodide} #| slideshow: {slide_type: fragment} number = 5 my_boolean = number > 0 while my_boolean: number = number - 1 my_boolean = number > 0 print("number is " + str(number)) ``` Let's compare this to an `if` statement - An `if` statement executes once if the Boolean is `True` - An `while` loop executes repeatedly until the Boolean is `False` ```{pyodide} #| slideshow: {slide_type: fragment} number = 5 my_boolean = number > 0 if my_boolean: print("Positive number") ``` ## Practical - We now move over to Python - Please open [week_03_home.ipynb](./week_03_home.qmd) - For the rest of today, you must work through a Python notebook - You have a choice of one of three options - [Option 1: Beginner - For and While Loops](week_03_loops_beginner.qmd) - [Option 2: Intermediate - Advanced Iteration](week_03_loops_intermediate.qmd) - [Option 3: Advanced - Comprehensions](week_03_loops_advanced.qmd)