DS4UX (Spring 2016)/Day 2 lecture

Resources

• Python data types cheat sheet
• Python loops cheat sheet
• state_capitals.py -- the state capitals example.
• cdsw-au2015-lecture1-20151010.ogv -- Professor Mako Hill's lecture video, which covers most of the concepts from today's lecture.

Lecture outline

Lists

• purpose
  • Stores things in order
• initialization
  • making a list called my list: my_list = ["a", "b", "c"]
  • comma separated elements. in python they can be a mix of any kind of types
  • type(my_list)
• len() review
• accessing elements
  • indexing like my_list[0]
  • indexing starts from the front and we start counting at 0 (now you understand all the zeros we've been using)
  • we go from the end with negative numbers
  • what happens if we try to move outside of the range? ('error!)
• adding elements
  • using the the my_list.append() function
  • the .append() function is a special kind of function that lists know about
• changing elements
  • replacing elements like my_list[0] = "foo"
• finding elements in list
  • e.g., "z" in my_list
• slicing lists
  • the colon inside the [] is the slicing syntax
  • e.g., my_list[0:2] is 0th up to, but not including, the 2nd
  • e.g., my_list[2:]
  • e.g., my_list[:2]
  • e.g., my_list[:]
• strings are like lists
  • we can slice lists
  • len()
    • len("") length of the empty string
• many other interesting functions for lists
  • e.g., min() and max()
  • e.g., create a list of names and sort it names.sort()

loops and more flow control

• for loops
  • e.g., for name in names: print name
  • e.g., for name in names: print 'hello ' + name
  • Super powerful because it can do something many many times. Data science is about doing tedious things very quickly. For is the workhorse that makes this possible.
  • Look and see name is after we're done looping.
  • Move to editor.
• if statements inside for loops
  • e.g., if name[0] in "AEIOU" then print "starts with a vowel"
  • show we can test things outside the loop to show how the comparisons are working
  • add an else statement to capture words that start with a consonant
  • append to a list within a for loop
  • create a counter within a for loop (keep track)
  • build up a sentence
• nested for loops
• range()
• while loops
• infinite loops
• if statements inside while loops
• break
• input()

dictionaries

• purpose
• initialization
• accessing elements
• adding elements
• changing elements
• keys() and values()

modules

• purpose
• builtins
• imports
• import random
• random.randint
• random.choice

walk through state_capitals.py

Where state_capitals.py from http://mako.cc/teaching/2015/cdsw-spring/state_capitals.py is the grand finale and synthesis of lecture material.