Software Designer Mindset

Question 1

Pure Functions

Answer 1

Pure functions have no side effects. They don’t change anything.
PureFunc(x,y) -> int:
Return x+y

Question 2

How to make an impure function more pure?

Answer 2

Customers = {Alice: phone: 1234}

SideEffectFunc() -> None:
Customers[Alice][phone] = 12345

Pass in the thing to be updated.
This also called dependency injection.

LessSideEffect(customers: dict[str, any])
//update customers

Question 3

Also ask when creating a function…

Answer 3

Is this a pure function. Does it have side effects, if so is there a way I can make it not have side effects such as providing the dependencies as arguments to the function.

Question 4

How can you make a class callable in python?

Answer 4

Use the __call__ dunder method

Question 5

What does it mean in python that everything is an object?

Answer 5

That literally anything can be treated as an object. Everything has accessible dunder methods. Everything is callable.
print((2).__class__) returns ‘int’

Question 6

Higher Order Functions

Answer 6

This idea relies on functions being objects that you can pass along and do something with.

So a higher order function is a function that gets another function as an argument or it can have a function as a return value.

Question 7

Given a function send_email(cx list) that takes in a list of customers checks if they are of a certain age and sends to only those cxs…

How and why would you make this into a higher order function?

Answer 7

Create another function is_eligible(customer) and pass this function into send_email(cx list, is_eligible)

This allows you to separate out the eligibility criteria from the email functionality.

Question 8

What are closures?

Answer 8

A function that you define within a function.

Question 9

What is one of the uses of python functools?

Answer 9

From functools import partial

newFunc = partial(existingFunc, param=25)

Take an existing function, apply ahead of time some of the arguments and you get a new function.

Question 10

A class is nothing more then a grouping of functions

But there is nothing stopping you from grouping functions in other types of data structures…

What types could you use to create a grouping of funtions?

Answer 10

Create independent functions.

Create a list, set, or tuple of the function names.

Use the list, set or tuple in another function to operate on values.

Question 11

What does the Iterable type in python mean?

Answer 11

It defines a type that is iterable and not changeable.

post_processors: Iterable[Callable[[int, cust], None]

Question 12

Instead of interfaces python has what?

Answer 12

Protocols

Question 13

What does super() do?

Answer 13

Allows you to call the method of a parent class from a derived class.

More specifically the super() takes you to the next object in the __mro__ list. Method Resolution Order

Question 14

What is the resulting MRO for the below classes.
Class A:
Class B(A):
Class C(A, B):

Answer 14

(A, object)
(B, A, object)
(C, A, B, object)

Question 15

super() == ?

Answer 15

Next in the line of mro

Question 16

Functional vs Unit Test

Answer 16

Functional tests the app from the outside user perspective

Unit tests the app from inside programmer perspective

Question 17

How does TDD approach functional and units test?

Answer 17

Start by writing a functional test describing the new functionality from the users point of view

Once you have a functional test that fails start to think about how to write the code that can get it to pass.

Now use one or more unit tests to define how the code should behave. Every line of production code should be tested by one of our unit tests.

Question 18

Composition vs Inheritance

Answer 18

Both are methods to establish relationships between classes and objects

Inheritance derives one class from another

Composition defines the class as the sum of its parts

Question 19

Inheritance is used for…

Answer 19

polymorphism, where you have a base class and want to extend its functionality

Question 20

Composition is a what type of relationship

Answer 20

has-a

Question 21

public class Job{}

How would you use composition to create a relationship with this class

Answer 21

public class Person{

private Job job; }

Person has-a job

Question 22

What type of relationship does inheritance create?

Answer 22

Is-a

Question 23

public class Animal{}

How would you use inheritance to create a relationship with this class.

Answer 23

public class Cat : Animal {

}

Question 24

Use inheritance only when you know the super class will…

Answer 24

Not be changed

Otherwise because the subclass is tightly coupled to the superclass there could be error introduced upon changes.