Python pt. 2

Python uses object-oriented programming

Objects are things, or represent things or system. Objects have their own methods and member functions

Kinds of objects (data types):

• String objects:

  • Can be stored within variables, in which case the name of the variable is the object, storing a string literal

  • All values of a string literal are indexed like a list, so if greeting=“Hello Python”, the function print(greeting[6]) will print the letter P, as that is the 7th value of the string literal and indexing values start at 0

  • Just because there are 2 l’s doesn’t meant they are indexed the same, when converting a string literal to a list

  • Using s=greeting[0:7] and then print(s) will print “Hello P”, where s represents a string object.

  • The command to store certain parts of a substring inside a variable can also be written simply as s=greeting[:7] which leaves out the 0. Same thing with the last value, s2=greeting [7:] stores “Python”

  • len() functions may also be used in place of number values

  • Negative numbers may also be used to index the values of a string, with the very last character being indexed as -1, counting down to the left for however many characters there are

  • Although string objects can be treated like lists, they cannot be changed like lists, meaning they are immutable

  • Just like a list, string objects can be used like lists are in loops. For instance,
    greeting=”Hello there!”
    for character in range(len(greeting)):
    print(greeting[character])

  • Built in string object functions:

    • .upper() will convert the whole string to capital letters

    • .title() which will convert only the first letter to a capital and all others to being lowercase

    • .split() will split a string apart, seperating them by whatever is in the parenthesis. If left blank it defaults to a space. If then creates a list of each of the split components. If text=”Hello Python!”, then print(text.split()) will display [‘Hello’,’Python!’]

    • ‘x‘.join(stringObject) is similar to .split, it will join different elements of a list generated from a string object together, using x as an insert between the two, and the list in ()

    • stringObject.replace(‘x’,’y’) will replace any character x with the character y in the string object stringObject

Operators:

• Relational operations:

  • > | Greater than

  • < | Less than

  • >= | Greater than or equal to

  • <= | Less than or equal to

  • == | equal to, not to be confused with =

  • != | not equal to

• Logical operators:

  • and | This checks if two things are both true

  • or | This checks if either of two things are true

  • not | This is the negation of something

If statements:

• Will only run certain code under the if statement if a certain condition is met

• If (condition) then (operation) | Will run code if a certain condition is true. Example:
  if favColor=teal:
  print(“Hey that’s my favorite color!”)

• If (condition) else (operation) | Will run code if a certain condition is false. Example:
  if num/2==2:
  print(“Your number is 4.”)
  else:
  print(“Your number is not 4.”)

• elif | stands for else if
  if (condition1)
  #Code that runs if condition1 is true
  elif (condition2)
  #Code that will only run if condition1 is false but condition2 is true
  elif (condition3)
  #Code that only runs if condition1 and condition2 and false, but condition 3 is true
  else
  #Code that runs if condition1, condition2, and condition3 are all false

• Compound if statements: Have 2+ conditions that are evaluated, use and + or

  Example:
  if (condition) and (condition):
  #Code that runs in both are true
  if (condition) or (condition):
  #Code that runs if either conditions are true

  if (condition) nand (condition)
  #Code that runs if both conditions are false
  if (condition) nor (condition)
  #Code that runs if either condition is false

While loops

• Uses ‘while’ to run code under it, like in an if statement, under the context that the condition is true

• Used in loops to run code multiple times, until a condition is false

• def whileExample():
  i=0
  while i<5:
  print(“Hello!")
  i=i+1
  #This code will print ‘Hello!’ 5 times, as until the 6th time in the loop the i<5 condition is true, each time the loop is run i increased by 1.

Digital number systems:

• Binary: Binary is base 2, uses 0s and 1s, and is denoted with the “prefix” 0b.

• Hexadecimal: Base 16, 0-F, denoted with the “prefix” 0x.

• The print() function can be used to convert things into base 10 numbers, using the indicated “prefixes”. Example print(0b1001) outputs 9.

• Bin(x) will convert a number x to binary. For example, b=bin(9) will store 1001 in b

• int(‘x’,y) converts a number x, which is base y, from a string to decimal.

• hex(x) will convert a number x into hexadecimal, similar to bin(x) with binary.

Storyboards:

• Also called pseudocode

• General “outline” for what the actual coding will be (UGH FUCK OUTLINES)

  0. Objective: Understand what program you are trying to code, what will it accomplish?

  1. Set up: What the different data types and variables you will need are, note if different things will need to be imported

  2. Generate a simple function: Establish which kinds of functions you will need, and pick a simple one. What will that simple function need to do

  3. Other functions: What are the other functions you will need? What is a simple outline for those functions, including their purpose and general process?