Control Structures

Session Overview

Loops
If/Then
Case
Try/Except
Decorators

Control Structures

How and Why to use control structures?

Sequencing
Decision Making
Repeat based on criteria
Deploy/Scale our functions

Conditional

Make decisions based on criteria: True or False
Decide between two (or more) paths based on input
if, if-else, switch (case), nested if statements…

Looping

Repeat block of code until condition is met
Perform task multiple times
Iterating through elements
for, while, do-while

Flow Modifications: break, continue, exit, goto, etc.

Session Overview

Loops
If/Then
Case
Try/Except
Decorators

Loops

For Loop: Iterate over a sequence of elements.

for variable in sequence:
    # code to execute for each element in the sequence

variable takes on value of each element in sequence.

What will this output?:

numbers = [1, 2, 3, 4, 5]
for num in numbers:
    print(num)

Loops: Applications

Where can we use loops? Where shouldn’t we use loops?

Iterating through elements
Bootstrapping
Simulations
?

Session Overview

Loops
If/Then
Case
Try/Except

If/Then

Execute code based on condition.

if condition:
    # code to execute if condition is true

> condition is an expression that evaluates to true or false.

Example:

num = 5
if num > 0:
    print("The number is positive")

What if we have alternatives?

if condition:
    # code to execute if condition is true
else:
    # code to execute if condition is false

Example:

num = -5
if num > 0:
    print("The number is positive")
else:
    print("The number is negative or zero")

Many Conditions

score = 75

if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
elif score >= 60:
    grade = "D"
else:
    grade = "F"

print("Your grade is", grade)

Is there a better way to do this?

Case/Switch Statements

lang = input("What's the programming language you want to learn? ")

match lang:
    case "JavaScript":
        print("You can become a web developer.")

    case "Python":
        print("You can become a Data Scientist")

    case "PHP":
        print("You can become a backend developer")
    
    case "Solidity":
        print("You can become a Blockchain developer")

    case "Java":
        print("You can become a mobile app developer")
    case _:
        print("The language doesn't matter, what matters is solving problems.")

Important Notes:

First case to evaluate to true wins!
Important to include default condition… what you want to happen if there is no match.

Conditional Applications

Where can we use conditional statements?

Data Filtering
Quality Control
Group Management
Decision Recommendations

Session Overview

Loops
If/Then
Case
Try/Except
Decorators

Try/Except

Error Handling!

Detect errors during runtime
Handle those errors during runtime

Examples:

try:
    x = 1 / 0
except ZeroDivisionError:
    print("Error: division by zero")

try:
    x = int("hello")
except ValueError:
    print("Error: invalid value")
except TypeError:
    print("Error: type mismatch")

try:
    x = 1 / 0
except ZeroDivisionError:
    print("Error: division by zero")
finally:
    print("Cleanup code")

Error Handling Applications

Where should you handle errors?

Session Overview

Loops
If/Then
Case
Try/Except
Decorators

Decorators

A Python function that takes a function as an argument and returns a new function.

Allow you to modify the functionality of a function by wrapping it in another function.

Decorator Syntax

Decorators are implemented using the “@” symbol followed by the name of the decorator function. They are placed before the function definition.

@decorator
def function():
    # function body

Making a Decorator

def my_decorator(func):
    def wrapper():
        print("Something is happening before the function is called.")
        func()
        print("Something is happening after the function is called.")
    return wrapper

@my_decorator
def say_hello():
    print("Hello!")

say_hello()

Decorator Applications

Logging
Authentication
Caching
Rate Limiting
Deployment
Scaling

Decorator Scaling

Note this is pseudo-code:

def launch_on_cloud(func):
    def wrapper(*args, **kwargs):
        spin_up_workers(num_instances, num_cpus, ram)
        result = func(*args, **kwargs)
        collect_results(result_location)
        return result
    return wrapper

@launch_on_cloud
def regrid_gid_point(dataset):
    ...

regrid_grid_point(netcdf_data)