Introduction to Coding and Data Analysis for Scientists

Week 4: Functions

Today’s Lecture

Lecture 4: Functions
- Recap: For and While Loops
- Functions
- Inputs and Outputs
- Practical

Important: Assessed Coursework 1

The first assignment has been released!
- 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: `for` and `while` loops

Loops can be used to simplify repetitive computation
- Last week, we saw an example where we wanted to print the square of each item in this list

We could write code like this…

Recap: `for` and `while` loops

Loops let us do all this automatically!

Motivation

Loops let you simplify code which repeats over and over again.
However, sometimes you have code that repeats itself in a less straightforward manner…
- Do some computation
- Run some other code
- Do the same computation again

In such cases, you might want to use a function
You can think of a function as a block of pre-prepared code that you might want to run over and over again.

Functions

Let’s look at an example.

You can think of this as a black box

You put a variable x in
It doubles x and adds 1
Then prints the result

Functions

Suppose we now run this code after the function.

This will run the code inside the function, but with x replaced by k.
- E.g. it will run:

y = k * 2 + 1
print(y)

Functions

We can use this function to simplify the code from earlier!

Motivation

Functions are useful for a number of reasons
- Reduce repetitiveness in code
- Help organise code
- Easier to edit, maintain and debug
- Makes code easier to share
- Improve readability

Inputs and Outputs

Instead of printing the result of our function, we can return it
This means that the function will “spit out” the value of y, and we can save it using the = operator

For this example:
- x is an input: A variable specified in the function definition
- y is an output: A variable given back using the return statement
You can have multiple inputs and outputs (we’ll cover this in the practical)

Practical

We now move over to Python
Please open week_04_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 4: Functions ## Today's Lecture - Lecture 4: Functions - Recap: For and While Loops - Functions - Inputs and Outputs - Practical ## Important: Assessed Coursework 1 - The first assignment has been released! - 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: `for` and `while` loops - Loops can be used to simplify repetitive computation - Last week, we saw an example where we wanted 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 write code 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) ``` ## Recap: `for` and `while` loops - Loops let us do all this automatically! ```{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 ``` ## Motivation - Loops let you simplify code which repeats over and over again. - However, sometimes you have code that repeats itself in a less straightforward manner... - Do some computation - Run some other code - Do the same computation again ```{pyodide} k = 3 y = k * 2 + 1 print(y) print("Doing something else here...") m = 10 + k z = m * 2 + 1 print(z) print("Sum of numbers:", sum([1, 2, 3])) w = 2 * 2 + 1 print(w) ``` - In such cases, you might want to use a `function` - You can think of a function as a block of pre-prepared code that you might want to run over and over again. ## Functions - Let's look at an example. ```{pyodide} #| slideshow: {slide_type: fragment} # This is a function: def print_double_and_add_one(x): # Double x and add 1 y = x * 2 + 1 print(y) ``` You can think of this as a black box - You put a variable `x` in - It doubles `x` and adds `1` - Then prints the result ## Functions - Suppose we now run this code after the function. ```{pyodide} #| slideshow: {slide_type: fragment} # This is a function: def print_double_and_add_one(x): # Double x and add 1 y = x * 2 + 1 print(y) # This is not part of the function, # because the code is no longer indented k = 3 print_double_and_add_one(k) ``` - This will run the code inside the function, but with `x` replaced by `k`. - E.g. it will run: ```python y = k * 2 + 1 print(y) ``` ## Functions - We can use this function to simplify the code from earlier! ```{pyodide} #| slideshow: {slide_type: fragment} k = 3 y = k * 2 + 1 print(y) print("Doing something else here...") m = 10 + k z = m * 2 + 1 print(z) print("Sum of numbers:", sum([1, 2, 3])) w = 2 * 2 + 1 print(w) ``` ```{pyodide} #| slideshow: {slide_type: notes} # Should be replaced with: # -------------------------- # # k = 3 # print_double_and_add_one(k) # # print("Doing something else here...") # # m = 10 + k # print_double_and_add_one(m) # # print("Sum of numbers:", sum([1, 2, 3])) # # print_double_and_add_one(2) ``` ## Motivation - Functions are useful for a number of reasons - Reduce repetitiveness in code - Help organise code - Easier to edit, maintain and debug - Makes code easier to share - Improve readability ## Inputs and Outputs - Instead of printing the result of our function, we can return it - This means that the function will "spit out" the value of `y`, and we can save it using the `=` operator ```{pyodide} # This is a function: def print_double_and_add_one(x): # Double x and add 1 y = x * 2 + 1 return(y) # <-------------- Now returned! # This is not part of the function, # because the code is no longer indented k = 3 z = print_double_and_add_one(k) print(z) ``` - For this example: - `x` is an `input`: A variable specified in the function definition - `y` is an `output`: A variable given back using the `return` statement - You can have multiple inputs and outputs (we'll cover this in the practical) ## Practical - We now move over to Python - Please open [week_04_home.ipynb](./week_04_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 - Defining Functions](week_04_functions_beginner.qmd) - [Option 2: Intermediate - Flexible Inputs and Outputs](week_04_functions_intermediate.qmd) - [Option 3: Advanced - Lambda Functions and Functional Programming](week_04_functions_advanced.qmd)

Week 4: Functions

Today’s Lecture

Important: Assessed Coursework 1

Noteable Submission

Recap: for and while loops

Recap: for and while loops

Motivation

Functions

Functions

Functions

Motivation

Inputs and Outputs

Practical

Recap: `for` and `while` loops

Recap: `for` and `while` loops