Unit Two - Intermediate Python

Part One - Functions & Parameters

• A function (also known as a method) is a reusable section of code written to perform a specific task in a program. 
• A method can take input in the form of parameters and output by returning data to whoever called it.
• A method header looks like this:
• Ex: def apple(num):
• Apple is the name of the method
• num is a parameter (input) for the method
• The body of a method is the code it contains
• Calling a method tells the program to find a method by the specified name and execute the code inside of it.
• There are two ways to pass a variable in computer science, depending on the language you use.
• Pass By Value (used in python by default, used in Java sometimes)
• Provides the method with a copy of the data.  As a result, when you modify the variable in the method, the original is NOT changed.
• Pass By Reference (used in Java sometimes)
• Provides the method with a reference to the memory address.  As a result, when you modify the variable in the method, the original in also changed.
• A method that has a variable number of parameters in python uses a feature called splat arguments.
• To gain access to new special functions, you can import a module to Python
• Some more useful functions:
• max() - returns the largest number from the set of parameters
• min() - returns the smallest number from the set of parameters
• abs() - returns a positive version of the parameter
• type() - returns the data type of the variable

Part Two - Lists

• Lists are a data type you can use to store a collection of different pieces of information as a sequence under a single variable name
• You can access an individual item on the list by its index. An index is like an address that identifies the item's place in the list
• List indices begin with 0, not 1! You access the first item in a list like this:list_name[0]. The second item in a list is at index 1: list_name[1]. Computer scientists love to start counting from zero.
• In Python, we say lists are mutable: that is, they can be changed.
• You can use the append() method to add things to an existing list
• You can use len() to get the length of a list, just like you can with a string
• If you only want a small part of a list, that portion can be accessed using a special notation in the index brackets.list_name[a:b] will return a portion of list_name starting with the indexa and ending before the index b.
• This slicing method works with strings, too!
• You can search through a list with the index()  function.my_list.index("dog") will return the first index that contains the string"dog". An error will occur if there is no such item.
  
• Items can be added to the middle of a list (instead of to the end) with theinsert() function.my_list.insert(4,"cat") adds the item "cat" at index 4 of my_list, and moves the item previously at index 4 and all items following it to the next index (that is, they all get bumped towards the end by one).
• You can use a for loop to go through each element in the list
• f your list is a jumbled mess, you may need to sort() it. my_list.sort()will sort the items in my_list in increasing numerical/alphabetical order.
• A dictionary is similar to a list, but you access values by looking up a key instead of an index. A key can be any string or number. Dictionaries are enclosed in curly braces.

Part Three - Loops

• The while loop is similar to an if statement: it executes the code inside of it if some condition is true. The difference is that thewhile loop will continue to execute as long as the condition is true. 
• An infinite loop is a loop that never exits.
• The break is a one-line statement that means "exit the current loop." An alternate way to make our counting loop exit and stop executing is with the break statement.
• Using a for loop, you can print out each individual character in a string or each element in a list.