What's in a Software Dev degree anyway? Course 1 - Information Structures

This is a continuation of What's in a Software Dev degree anyway?. Again, expect examples with no math and no crappy names

Okay, I did it. First class of this degree is done. This post is just a cumulative of topics and concepts that were covered in my 1st course of my Software Dev degree.

As of now, I'd still consider myself self-taught. It's rough not knowing what you should learn next. I have a lot of gaps in my knowledge. That's why I decided to go to school. And also why I'm hoping sharing this will help someone else.

MET CS 521 O1 Information Structures with Python (2021 Fall 1)

Jump to:

• Input (Learning Objectives)
• Output (Projects and Work)
• Documentation (References)

Wait! I just wanna test myself on the exercises you had in class. Glad you asked, here's the repo: Exercises for first class

Input (Learning Objectives)

Week 1

• Data Types
  • primitives vs collections
  • primitives: int bool float complex char
  • collections: list tuple set dictionary string
• Namespaces
• Input/Output
• Variable Scopes (legb)
• Importing modules
• statements dog_age = 6 vs expressions dog_age + 1
  • statement returns nothing
  • expression returns something, also called a side effect
• Functions that can be applied to different data types are polymorphic

Unrelated to the curriculum, I also learned:

• the professor has a preference for explaining Python in relation to C++ instead of explaining in ways everyone can understand.

Vicki Langer

@vicki_langer

Am I in the wrong class?! I swear I’ve learned more about C++ than what I actually signed up for

22:21 PM - 09 Sep 2021

• use RateMyProfessors.com to look up before registering for future courses. I was watching Netflix series “The Chair” and learned about this.

Week 2

• Data Types
  • complex numbers
    • totally new to me. Guess they’re used in things like electromagnetics, chemistry, and economics.
• fractions module is super neat
• Hashing hash() for quick comparisons (still confused on this)
• Mutability
• Python Ranges
• Copying Objects
  • shallow copy makes copy but points to other object
  • deepcopy() makes new object
• == vs is
  • == checks values
  • is checks id to see if same exact object

Week 3

• UTF - 8 numbering for alphanumeric characters
  • chr() and ord()
• Strings
  • immutable, but there are work arounds
    • range(start, stop, step)
    • half-open range: does not include stop number
    • slicing [start:stop:jump]
    • string reversal string[-1]
    • out of bound slicing will not error, but give you whatever is in bounds
    • string formatting {:[alignment][width][decimal precision][type descriptor]}
• Control Flow
  • if-elif-else
  • try - except
• Iterations
  • while and for
• Files
  • open,read, readlines, write, writelines
  • importance of close
• Lists
  • list comprehensions
    • can have multiple conditions
    • works for mutable objects (lists & sets, not tuples & strings)

numbers = [13, 72, 11, 43, 66, 82]

# iterate to get even numbers
evens_from_nums = []
for num in numbers:
    if num % 2 == 0:
        evens_from_nums.append(num)

# list comprehension to get even numbers
# same as above, just shorthand
odds_from_nums_again = [num for num in numbers if num % 2 == 0]

• list reversal with slicing or .reverse()
• enumerate() for indexed collections
  • returns a list with an index number
• sort() vs sorted()
  • sort() changes things in place
  • sorted() orders things and creates a new list

Week 4

• Lists
  • See above, went over some list stuff in week 3
  • indexing a nested list list[1][2] would give index 1 of main list then index 2 of the nested list
  • sorting list of list sorts on the index [0] of nested lists
  • some methods that modify a list: append() pop() extend() insert() remove() sort() reverse()
  • reversing a list list[::-1] (gives no start or stop and a -1 step)
  • Exercise: check if words are anagrams
  • create a copy slice using [:] (shallow copy?)
  • when list appends itself as an element, infinite regress occurs
• Tuples
  • single element tuple tuple = ("cat",) note the trailing comma, otherwise this would not be a tuple
  • can use the same set up for a list comprehension
  • immutable but can contain mutable objects
  • tuples use most of the same methods as lists, except the ones that would change a list (eg append())
• Dictionaries
  • can use a similar set up for a list comprehension
  • keys are not arranged in a specific order, they are in an order to efficiently search
  • Exercise: count words or letters in a string
  • namespaces are implemented with dictionaries
  • items() all key-value pairs as a list of tuples
  • keys() all keys as a list of list
  • values() all values as a list of list
  • zip() 2 or more lists together. Tuples by default
  • can merge dicts with update() (note: for keys that already exist, values will be replaced)
• Sets
  • mutable, not ordered, only unique values
  • subset small_set <= big_set vs superset big_set >= small_set
  • frozen sets are possible to make sets immutable
  • Methods
    • & or intersection() creates new set of all elements that are the same
    • | or union() creates new set of all elements of both lists
    • - or difference() creates new set of all elements in 1st set but not 2nd set
    • ^ or symmetric_difference() creates new set of all elements that are different
    • Link to Python Tutor with examples (with animals) of these set methods
  • split() returns a list
  • data type is the actual use of data structures, where data structures are more the theory or idea of
  • efficiency refers to time, space, and algorithm
  • Implementing other data structures with the types we have
  • stacks can be made with lists
  • Ternary if basically an if-else but jammed onto one line

true_thing if condition else false_thing  # ternary syntax
throw_ball() if dog_wants_play else pet_dog()  # ternary example

Week 5

• Error Handling
  • interupts vs Exceptions
  • Allows us to watch code for errors
    • useful for things like user inputs ("All user input is evil")
  • Try - Except
    • can handle multiple exceptions
  • can do except IndexError as e to later use e (the error)
  • If you use finally it runs every time, not required though
• Functions
  • functions are objects and have their own namespace (reminder: everything is an object)
  • function docstring can include inputs, outputs, what the function does
  • Parameters != arguments
    • parameters are in the function definition def feed_dog(dog_weight):
    • arguments are in the function call/invocation feed_dog(25.5)
  • functions return None if there is no return statement
  • can pass functions as arguments
  • possible to have different function "signatures". same name === same function
  • default parameters def pet_cat(time="now"): if you don't give a different time, cat will be pet now
  • variable positional args def func(*args): this requires a tuple as input
  • Mutable parameters as args/params, avoid if possible. Can cause issues
  • parameter names as keywords feed_dog(dog_age=5, dog_weight = 25.5)
  • annotation of params to document/suggest what type the param should be def feed_dog(dog_weight: float, dog_age: int):

 #syntax
 def function_name(param1, param2):
     '''what it does, inputs, and outputs'''
     # code for your function to do
 function_name(arg1, arg2) 

 # example
 def feed_dog(dog_weight: float, dog_age: int):
     '''calculate/output how much to feed dog with given dog weight arg'''
     pass
 feed_dog(25.5, 5)

 # -----other ways to call/invoke-----
 # how to invoke with out of order args
 feed_dog(dog_age=5, dog_weight = 25.5)  # also useful when there are a lot of params
 # use a dictionary for function args
 dog_dict = {"dog_weight":25.5, "dog_age":5} # same names as params
 feed_dog(**dog_dict)  # using ** to pass a dict

• generators functions
  • use yield instead of return
  • allows you to start where you pick up as opposed to the beginning like a return
  • yield give results and wait until next time function is called
  • __iter__() __next__()

• Lambda Function

  • lambda args: expression

• map() filter() reduce()

• Recursion

  • must have a base case and the base case must be first in the function
  • can be slower than a non-recursive function
  • Advantage: less code, may be easier for some problems
  • Disadvantage: inefficient on memory and processing time, harder to read and follow
    • Calls by...
    • if you pass a mutable param -> call by reference
    • create a new object -> call by values
    • if you pass a immutable param -> call by value ### Week 6

• Classes

  • can be used to make new data structures. (Classes were used to build dict(), set(), list() etc)
  • defining a class:
  • self allows an object to keep it's own data (like this in js/c++/java)

import copy
class Dog():
    __stomach = 1  # a static variable w/ name mangling
    # define a constructor
    def __init__(self, name):
        self.__name = name  # w/ name mangling

    def __copy__(self):  # shallow copy 
        return Dog(self.__name)  # w/ name mangling

    def __str__(self):
        '''give a string when you print(instance_variable)'''
        return 'dog with name: ' + str(self.__name)  # w/ name mangling
    def add(a,b):  #
        return Dog(a.__name + b.__name)
    def get_stomachs(self):  # getter/accessor
        return self.__stomach

    def eat_dinner(self):  # self is like `this` in js/c++/java
        '''a class method for the dog to eat dinner'''
        # use Class_Name.variable to get the static variable
        print(f"{name} reports for dinner with their {Dog.stomach} stomach")

dog_one = Dog("wiley")  # makes a Dog just like list() makes a list
dog_one_come = dog_one.eat_dinner()
dog_copy = copy.copy(dog_one)
print(dog_one)  # prints return of __str__

• Static vs. Instance Variables
  • better to have static variables vs instance variables
  • better to have 1 copy of a variable as opposed to 1 copy per instance
  • static vars are before the methods defined in a class
  • instance var or non-static would have the var in a method and each instance would have it's own copy of the var making it not so efficient
  • __repr__() "official" object description (example: <__main__.Dog object at 0x7f545b6db8d0>)
• Data Encapsulation
  • no private like java
  • all methods and variables are public
  • name mangling provides minimum protection
    • give __ before name like __stomach to prevent accidental changing.
    • Though you could still change Dog._Dog__stomach = 4 it would just be less of a chance to do it by accident
• Overloading
  • Could write a method to use +,-,<,>,==,!=,&,! in a way they weren't already built to do by using "magic methods"
  • magic methods are just overwritten methods that overload operators?

    def add(self, other):  # 
        return Dog(self.__name + other.__name)

• Inheritance and Polymorphism
  • can derive classes from new classes.
  • In real life, mammals could be a parent class and cats could be a child class. Cat has some similarities, but some stuff is different
  • if child class doesn't have a str() defined, python will look in the parent class
  • functions like print() and len() can be used across different classes and functions
  • if inheriting a parent class, include in the constructor/__init__
• Multiple Inheritance
  • python allows classes to have multiple parent classes. not all languages allow this (like Java and C)
  • one problem

• Abstract Classes

  • Link to Python Tutor with examples (with animals) of abstract classes

• Unit Tests

  • run your function and use assert statements to test the expected output

Output (Projects and Work)

Week 1

assignment

quiz

The quiz had some ridiculous questions on it. Oh well.

Vicki Langer

@vicki_langer

Bombed that first quiz.

Python is interactive? Sure. I guess that’s important enough to have 2 questions on it.

When are sytax errors given? On compile or runtime? Who cares? They’re automatic!

Now I’m being childish, I guess I missed these in the book 😩

15:11 PM - 10 Sep 2021

Week 2 (data types, casting, mutability)

assignment

Homework 2 Assignment PDF

Week 3 (strings, control flow, loops, files)

assignment

Homework 3 Assignment PDF

Week 4 (lists, tuples, dictionaries, sets)

assignment

Homework 4 Assignment PDF

Week 5 (error handling, functions, recursion, generators)

assignment

Homework 5 Assignment PDF

Week 6 (classes, overloading, ecapsulation)

assignment

Homework 6 Assignment PDF

Week 7

Final Project

Final Project Requirements
Final Project

Final Exam

15 questions and 30 minutes later.
Covered:

• generators
• nested list/tuple indexing
• function syntax
• slicing
• hashable and immutable data types
• break and continue
• classes and inheritance

Documentation (References)

• https://pythontutor.com/visualize.html#mode=edit
• https://docs.continuum.io/anaconda/install/