Other Data Types Primer

Announcements

• Problem Set 1 is due on Monday!
• I’ll introduce Pensieve AI Tutor in the class today
  • I’ll try to deploy Problem Set 2 using Pensieve. So complete the _practice exercises to get you set up for next week’s assignment
• Don’t forget you can contact your section leaders to ask questions if you need help!
• QUAD Center is a great place to seek for help too! Check their schedule here
• If you have just added the course and not in section yet, see me immediately
• Polling today! Use this link
  • Be consistent, use firstname

Review Question

What is the printed value of A in the code below?

>>> A = 10
>>> B = 5 % 3
>>> C = A * B ** B
>>> A -= B + A // 2
>>> A, B, C = C, A, B
>>> print(A)
??

Other Data Types

• Numbers are great, but what about other types of data?
• We will spend considerable time on the details of these data types later
• For now, let us introduce:
  • strings!
  • lists!

A quick String primer

• A string in Python represents textual data, in form of a sequence of individual characters
  • Domain: all possible sequences of characters
  • Operations: Many! But we’ll keep in quite simple initially
• Denoted by placing the desired sequence of characters between two quotation marks
  • 'I am a string'
  • In Python, either single or double quotes can be used, but the ends must match
    • "I am also a string!"
    • "I'm sad you've gone"

Lists

• A list in Python represents a sequence of any type of data
• Denote by bordering with square brackets ([, ]) with commas separating each element of the sequence
  • Each element could be any data type (even mixing from element to element!)
  • ['This', 'is', 'a', 'list']
  • ['Great', 4, 'storing', 5 * 10]
• There are many operations that we will see are possible on lists, but will start with only the basics

Sequences

• Both strings and lists are examples of a more general type called a sequence
  • Strings are sequences of characters
  • Lists are sequences of anything
• Sequences are ordered, so we can number off their elements, which we call their index
  • Counting in Python always starts with 0, so the first element of the sequence has index 0
• Python defines operations that work on all sequences
  • Selecting an individual element out of a sequence
  • Concatenating two sequences together
  • Determing the number of elements in a sequence

Selection

• You can select or “pluck out” just a single element from a sequence using square brackets [ ]
  • There are no commas between these square brackets, so they can’t be confused with a list
  • The square brackets come after the sequence (or variable name representing a sequence)
  • Inside the square brackets, you place the index number of the element you want to select

>>> A = [2, 4, 6, 8]
>>> print(A[1])
4

>>> B = "Spaghetti"
>>> print(B[6])
't'

Concatenation

• Concatenation is the act of taking two separate objects and bringing them together to create a single object
• For sequences, concatenation takes the contents of one sequence and add them to the end of another sequence
• The + operator concatenates sequences
  • This is why it is important to keep track of your variable types! + will add two integers, but will concatenate two strings

  >>> 'fish' + 'sticks'
  'fishsticks'

  >>> A = [1, 'fish']
  >>> B = [2, 'fish']
  >>> print(A + B)
  [1, 'fish', 2, 'fish']

Lengths

• The number of elements in a sequence is commonly called its length, and can be given by the len( ) function

• Simply place the sequence you desire to know the length of between the parentheses:

  >>> len("spaghetti")
  9

• You can have sequences of 0 length as well!

  >>> A = ""
  >>> B = [ ]
  >>> print( len(A) + len(B) )
  0

Understanding Check

A = "hots"
B = ["fire", A + A]
C = A[3] + A[1]
B += C + C[0]
D = B[0] + B[1] + B[2]
print(len(D))

Running a Program

• Python programs specify what part of the code is supposed to be when a program is run using a few special lines at the end of the program

  if __name__ == '__main__':
      function_to_run()

  • function_to_run is the name of whatever function you want to execute when the program is run

• Patterns of this sort are commonly called boilerplate

  • Less important to fully understand all the pieces of it now
  • Is important to understand what it is doing and how to implement it correctly

Sample Program

NUM_ODDS = 100 # Constant, so using all caps

def print_odds():
    """
    Prints the first NUM_ODDS odd numbers 
    starting at 1.
    """
    value = 1
    for i in range(NUM_ODDS):
        print(value)
        value += 2

if __name__ == '__main__':
    print_odds()

An adding program

# File: AddTwoIntegers.py

"""
This program adds two integers entered by the user.
"""

def add_two_integers():
    print("This program adds two integers.")
    n1 = int(input("Enter n1? "))
    n2 = int(input("Enter n2? "))
    total = n1 + n2
    print("The sum is", total)

# Startup boilerplate
if __name__ == '__main__':
    add_two_integers()

Visiting the library(ies)

• A huge strength of Python is that it offers a very large number of code collections called libraries
  • Can save you the effort from writing that code yourself!
• Requires you to import that library, which can take several different forms

  • Most common is to use import to grab everything in a library

    import math

    • You must then access any function in that library using its fully qualified name, which includes the library name (var = math.sqrt(4))

  • Can also use from ... import to grab specific functions from the library

    from math import sqrt

    • You do not need to use the library name then when you call it (var = sqrt(4))

Useful math definitions

Class Activity

• I’m introducing Pensieve AI Tutor in this class to:
  • try out how an intelligent tool can better facilitate your understanding
  • give you more hands on experience through class engagement

Class Activity

• Use this invited link to access your Pensieve Tutor student page
  • If prompted, login with your willamette.edu email