Chapter 10 - Let’s write some Code #

Starting Minimal #

Code is mostly math #

Heres the thing: Code is mostly math. If you’re anything like me, you probably just went ugggggghhhhhhh.

And I get it. But it’s not that bad for two reasons:

1. The math isn’t like what you’re used to.
2. The math is actually doing something. You’re not just getting a number to solve a problem, you’re making a tool that can solve many problems or watching the math cause something to happen on screen.

On point 1., it’s usally because code has lots of flow control and logic that you’re probably not used to seeing in math.

Things like

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if x is equal to y:
	set x to x-1
else:
	set x to y

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while Alice and Bob are Connected:
    exchangeMessages(Alice,Bob)

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if x == y:
	x = x-1
else:
	x = y

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while Alice.isConnectedTo(Bob):
    Alice.Message(Bob, "Hello")

But, what about point 2.? Take a look at this:

Python #

[TODO] Why start with python

The building blocks of programming #

All programming is just chaining logic, for example using treatments like “if a is b, then make c hold the value of a-3” followed by “if c is negitive then say hello”

Well, that’s actually an easy program

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a = 1
b = 1
c = 1

if a == b:    # Why are there two equal signs here?
    c = a-3

if c < 0:
    print('hello')

you should notice a few weird things here though, namely, on line 5 we used two equal signs to check equality. This is the case in most programming languages because a single equal sign, like is used on the first two lines, is used for assignment that is assigning the value of a to 1 and b to 1 or as on line 6 assigning the value of ( a - 3 ) to c, because we’ve already used a single equal sign for assignment, two equal signs is used for checking that two things are actual equal. That is, one equal sign sets things to be equal, two checks that they are equal.

If you follow the logic here, a and b are both 1, so line 5 checks that to be true, so line 6 does happen. Now ‘c’ which previously held the value ‘1’ is now equal to ‘a-3’, where ‘a’ is ‘1’, so ‘c’ becomes ‘-2’. on line 8 we check if ‘c’ is less than ‘0’, and because it is we print the word ‘hello’. Here, you’ll notice ‘hello’ is in quotes. This is because if it were not, that is if it were print(hello) it would try to print the value of the variable ‘hello’ which since hello isn’t defined, wouldn’t work. Let’s try this in the Python interpreter. You can find install instructions for your operating system here: https://www.python.org/downloads/. If you’re on Linux simply type python into the terminal.

With the Python interpreter open try without quotes:

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>>>print(hello)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'hello' is not defined

As you can see Python failed to print hello because the variable was not defined. Now lets try assigning a value to the hello variable before printing:

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>>> hello = "Hello World!"
>>> print(hello)
Hello World!

Anything you write to the interpreter can also be added to a file and ran that way. Try saving the examples above to a file called test.py, opening a terminal and running it with python test.py.

Conditions using if, elif and else #

You often want code only to be executed, if a certain condition is met. For example, take a look at the following code:

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a = 13
b = 27
if a > b:
    print("a is bigger")
else:
    print("b is bigger")

Using the if statement, connected with a logical condition, you can control the program flow. In this case, a is smaller than b, so python will skip the code inside of the if case and only execute what is within the else part.

You can also combine multiple if cases like this:

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a = 3
if a < 0:
    print("a is negative")
elif a == 0:
    print("a is zero")
else:
    print("a is positive")

Using the elif statement, you can check for another condition if the one in the if statement was false.

Loops #

Some lines of codes have to be repeated very often. Instead of typing the same line over and over again, you can use loops. There are two types of loops: The for and the while loop. While they both basically do the same thing, sometimes it is more intuitive to use one over the other.

TODO: Again on 0-based vs. 1-based indexing

The for loop #

The for loop iterates over a list of items and stores the current element in a variable. This is especially useful when working with lists, for example.

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fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print("I am eating a " + fruit)

If you are familiar with loops in other programming languages (such as Java or C), you’re probably thinking: “That’s not a for loop, that’s a for-each!”. This is true, in python all for loops are for-each loops. If you want to iterate over a range of numbers, use pythons range() function:

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for i in range(0, 100):
    print(i)

The while loop #

The for loop is very useful, but sometimes, using the while loop is easier and more straightforward. For example, if you want to repeat something until a certain condition is met, using this loop is simple:

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i = 0
while i < 10:
    print(i)
    i += 1

You can also combine the condition after the while keyword with an else statement:

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i = 11
while i < 10:
    print(i)
    i += 1
else:
    print("i is bigger than 10!")

[TODO] assignment, comparison, combined ops (+=), mod, exponent, floor, in/not in, is/is not, data types, functions libraries

Common methods used #

commenting-out print debugging Recursion, object orientation while(true) try/catch

Some simple programs #

Hello World #

As seen in the example above, the following will print Hello World!: print('Hello World!') Lets get some input aswell:

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print('What\'s your name?')
# This prints the question. Notice the escape character \ is used to avoid stopping the string. 

print('Hello ' + input()) 
# This will pause the program and wait for user input before printing Hello <input>

Even or Odd #

Below is an example of a Python script which checks if the input number is odd or even.

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# A number is even if division by 2 give a remainder of 0.
# If remainder is 1, it is odd number.
num = int(input("Enter a number: "))
if (num % 2) == 0:
   print("{} is Even".format(num))
else:
   print("{} is Odd".format(num))

Prime Numbers #

Prime number is a number greater than 1 whose only factors are 1 and itself. Few instances of prime numbers include 2, 3, 5, 11. Below is an example of python function which defines whether the given input number is prime or not.

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def is_prime(num):

    if num > 1:

        # Iterate from 2 to n / 2
        for i in range(2, num // 2):

            # If num is divisible by any number between
            # 2 and n / 2, it is not prime
            if (num % i) == 0:
                print("{} is not a prime number".format(num))
                break
        else:
            print("{} is a prime number".format(num))

    else:
        print("{} is not a prime number".format(num))

Calculating sine and pi #

Sorting a list #

Palindromes #

Cypher #

Making a full project #

Part 0, Git #

Before we get started, I want to be sure you took the time to read the section on Git in Chapter 6.1 above. If you need to refer to a cheat sheet you can look in Apendix B.

Part 1, Starting easy #

[TODO] guide to write an OO python program with libraries to read and write entries to a database-like file and a real database the database should have 3 tables, a to-do list, a time-tracker list, and a list of articles

To-do: NAME, DUEDATE time-tracker: 2types, either manually enterend with NAME, TSTART, TSTOP or NAME, TTOTAL for the following program articles: NAME, PUBLISHED, TPUB, TEDIT

we’ll need some way to track what items in the time tracker were started, but never stopped

for now, everything should be strictly command line arguments and print statments

More advanced topics #

[TODO] Move this section

Lambdas #

A lambda expression is used to create a a small anonymous function. It can take any number of arguments, but can only have one expression. Below is an example of a lambda expression which can be used to compute cube of any given number.

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>>> cube = lambda x : x**3
>>> cube(5)
125

And here is the other example of a lambda expression with three arguments.

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>>> sum = lambda a, b, c : a + b + c
>>> sum(1,2,-3)
0

threads/ parrallelization(high level only), interupts (actually, let’s save this until embbeded), apis,

A little more practice #

Weird projects

Easing into Graphical Programming with Creative Coding #

http://feed.grantcuster.com/

Coding Adventure: Ray Marching (YouTube)

Coding Adventure: Marching Cubes(Youtube)

Coding Adventure: Portals (YouTube)