Editing Community Data Science Course (Spring 2015)/Day 2 Lecture

== Resources ==

* [[Python data types cheat sheet]]
* [[Python loops cheat sheet]]
* [http://mako.cc/teaching/2015/cdsw-spring/state_capitals.py state_capitals.py] -- the state capitals example.

== Lecture outline ==

=== Review Friday material ===

* math: using python as a calculator
**addition, subtraction, multiplication, division
**division shows something different: <code>8/2</code> versus <code>2*2</code>
* <tt>type()</tt>
** there are different types of things in python (called objects)
** variables that "know about the decimal place" (int) and variables that don't (floats)
* variables
** assignment of variaibles
** e.g., math with variables: scale up a recipe, into an assignment
** you can assign to a variable and it will replace the old value
* strings
** things within quotation marks
** adding strings with "concatination" (smushing things together)
** e.g., <code>print("Hello" + name)</code>
** concatenating strings and integers don't work (e.g., <code>print(1 + "mako")</code>)
** 1 is different than "1"; name is different than "name"
** single quotes versus double quotes (python doesn't care)
** you can also multiply strings! (although it's not clear why you want to weird)
* booleans
** comparisons (e.g., <code>1 == 1</code> or <code>1 == 0</code>)
*** you can compare strings (case sensative!)
*** also >, <, and !=
** type() shows that the output of True or False is <code>bool</code>
** e.g., <code>"i" in "team"</code>
** e.g., "i" not in "team"</code>
* <tt>if</tt>/<tt>elif</tt>/<tt>else</tt> ('''move to external file''')
** if, something that evaluates to a boolean, and then colon
** e.g., <code>if "mako" in "makoshark"</code>
** e.g., adding else example: <code>if brother_age > sister_age</code>
** e.g., tempreature range
** e.g., adding elif: fix the bug in the previous program if they were the same age
** indent with spaces (we use 4 spaces!)
* functions
** has a parentheses
** we've already learnd examples of this: exit(), help(), type()

=== Lists ===

* purpose
** Stores things ''in order''
* initialization
** making a list called my list: <code>my_list = ["a", "b", "c"]</code>
** comma separated elements. in python they can be a mix of any kind of types
** <code>type(my_list)</code>
* <tt>len()</tt> 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 <code>my_list.append()</code> function
** the <code>.append()</code> function is a special kind of function that lists know about
* changing elements
** replacing elements like <code>my_list[0] = "foo"</code>
* finding elements in list
** e.g., <code>"z" in my_list</code>
* slicing lists
** the colon inside the [] is the ''slicing syntax''
** e.g., <code>my_list[0:2]</code> is 0th up to, but not including, the 2nd
** e.g., <code>my_list[2:]</code> 
** e.g., <code>my_list[:2]</code>
** e.g., <code>my_list[:]</code>
* strings are like lists
** we can slice lists
** len()
*** <code>len("")</code> length of the empty string
* many other interesting functions for lists
** e.g., <code>min()</code> and <code>max()</code>
** e.g., create a list of names and sort it <code>names.sort()</code>

=== loops and more flow control ===

* <tt>for</tt> loops
** e.g., <code>for name in names: print name</code>
** e.g., <code>for name in names: print 'hello ' + name</code>
** 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.''
* <tt>if</tt> statements inside <tt>for</tt> loops
** e.g., <code>if name[0] in "AEIOU"</code> 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 <tt>for</tt> loops
* <tt>range()</tt>
* <tt>while</tt> loops
* infinite loops
* <tt>if</tt> statements inside <tt>while</tt> loops
* <tt>break</tt>
* <tt>input()</tt>

=== dictionaries ===
* purpose
* initialization
* accessing elements
* adding elements
* changing elements
* <tt>keys()</tt> and <tt>values()</tt>

=== modules ===
* purpose
* builtins
* imports
* <tt>import random</tt>
* <tt>random.randint</tt>
* <tt>random.choice</tt>

=== 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.