Update a bit for Python 3 course.

Codecademy.md

@@ -10,13 +10,13 @@ It's gratis and accepts Python 3 syntax.
 
 https://discuss.codecademy.com/t/what-does-it-mean-that-python-is-an-object-oriented-language/297314
 
-# Errors (ex5)
+# Errors (ex6, CH1, P3)
 
-"Mismatched quotes will cause a SyntaxError'
+  "SyntaxError means there is something wrong with the way your program is written — punctuation that does not belong, a command where it is not expected, or a missing parenthesis can all trigger a SyntaxError.
 
-"SyntaxError: EOL while scanning a string literal"
+  A NameError occurs when the Python interpreter sees a word it does not recognize. Code that contains something that looks like a variable but was never defined will throw a NameError."
 
-No quotes will cause a NameError (interprets strings as commands. )
+  SyntaxError example: `SyntaxError: EOL while scanning string literal`
 
 # Math (ex6)
 
@@ -26,6 +26,8 @@ amazing_subtraction = 981 - 312
 trippy_multiplication = 38 * 902
 happy_division = 540 / 45
 sassy_combinations = 129 * 1345 + 120 / 6 - 12
+exponents = (16 ** 0.5) # 16 to the 1/2th power. (4)
+remainder = (15 % 2) # The remainder (and thus the result) equals 1
 ```
 
 ## Find the remainder of a number using %
@@ -57,19 +59,87 @@ Are indicated by # or """This is not for running"""
 
 An integer is like `5`, a float is a number with a decimal point like `5.0`. They can also be in scientific notation like `2.3e7`
 
-To make sure math like `7/2` = `3.5` is correct is by inputting it into Python like `7./2.` or `float(7)/2`
+In Python 2, you need to make sure math like `7/2` = `3.5` is correct is by inputting it into Python like `7./2.` or `float(7)/2`
+
+## Limitations of floats
+
+Floats are limited by the number of digits. For example `1/3 = 0.3`
+
+```
+>>> format(math.pi, '.12g')  # give 12 significant digits
+'3.14159265359'
+
+>>> format(math.pi, '.2f')   # give 2 digits after the point
+'3.14'
+```
 
 # Strings
 
-Multi-line strings are marked by ```"""Mulit-
+Multi-line strings are marked by
+```"""
+Mulit-
 line
-strings"""```
+strings"""
+```
 
 # Booleans (True/False)
 
 True = int(1)
 False = int(0)
 
+# Datatypes
+
+Force treating as a string: str(7)
+Force treating as an integer: int("7")
+Froce treating as a float: float(7)
+
+# Escaping Characters
+
+Simply add a `\` to escape a character that would otherwise cause issues.
+
+# Arrays / Indexes
+
+`cows = "cows"[0]`
+
+This sets the variable `cows` to the 0th letter of the string `"cows"` which is `c`. These indexes start at 0, not 1.
+
+# Strings
+
+## String Methods
+
+`len(var)` Get length of string.
+
+`var.lower()` Force lowercase
+
+`var.upper()` Force uppercase
+
+`str(var)` Force treating variable as a string.
+
+If it uses dot notation like `.lower()`, it works exclusively on strings.
+
+## Concatenation
+
+`"Ten times a cow is equal to " + result + " with 10 times as many breeding opportunities."`
+
+## String Formatting with %
+
+  `"%s %s - 2020" % (month, day) # Replace %s with a variable. First the month, then the day.`
+
+  `Add %03d to specify a signed integer padded 2 places with zeros. For example, 2 becomes 02.`
+
+  This is super useful for displaying dates like this: `print("%02d-%02d-%02d") % (now.month, now.day, now.year)` or time like this: `print '%02d:%02d:%04d' % (now.hour, now.minute, now.second)` (Ch3, Ex. 4)
+
+## Date and Time (Ch3)
+
+Grab the current time:
+```
+from datetime import datetime
+now = datetime.now()
+year = now.year
+month = now.month
+day = now.day
+```
+
 # Fun Projects
 
 Design a shop using Ex7 and Ex9 as a frame:
@@ -92,3 +162,14 @@ price_per_cucumber = 3.25
 total_cost = cucumbers * price_per_cucumber
 print(total_cost)
 ```
+
+Cool concept from Ch2 Ex15:
+
+```
+name = raw_input("What is your name? ")
+quest = raw_input("What is your quest? ")
+color = raw_input("What is your favorite color? ")
+
+print "Ah, so your name is %s, your quest is %s, " \
+"and your favorite color is %s." % (name, quest, color)
+```