Lists and Loops


Advanced Control Flows

Review


  1. What are Boolean Values?
  2. What are Boolean operators and expressions?
  3. How do IF statements work?

Lists


A list is a more complex Python data type
It is an ordered sequence (or container) of values 
marked by opening and closing brackets

demo_list = [2,  "some string",  True,  4,  5,  None]


Lists can be nested (an item in a list can be a separate list)

nested_list = [5,  7,  [99, "test"]]

List Indexing


Because lists are ordered, 
we can search for items at particular locations.
This is called "Indexing"

colors = ["blue", "black", "red", "green"]

# The first element in a list is located at position 0blue = colors[0]
red = colors[2]
green = colors[-1]
# same applies to strings, which are also ordered sequencestest_string = "hello world"letter_h = test_string[0]

List Slicing


In addition to looking up items at particular indexes, 
we can also retrieve multiple items at different position.
This is called "Slicing"

colors = ["black, "blue", "green", "orange"]first_three_colors = colors[0:3]alt_approach_for_first_three = color[:3]final_two_colors = colors[3:]

List operations


We can add, remove, alter, sort and perform several other operations on lists using built in functions
 my_scores = [] # use the append() function to add an item to a list my_scores.append(89) my_scores.append(70) # use the remove function to remove() to eliminate an item my_scores.remove(89)
 # Use indexing to alter an item my_scores[0] = 65

For loops


What if we want to perform an action on 
all the elements in a sequence?
The answer is a for-loop

 for some_variable_name in [33, "Bob", None, True]:     print some_variable_name

For-loops run their body code for each item in a sequence.
In this case, the print statement is called 4 times 
and each time, the item is assigned to some_variable_name

For loops Advanced


We can abruptly exit a for loop or alter it's flow
with break and continue statements respectively

 for i in range(10):    if i == 2:        continue    elif i == 5:        break    print i


While loops


Hybrid of Conditional Statements (IF/ELSE and LOOPS)

 while [boolean expression ==True]:
    # execute this loop body
    # over and over again

While loops are not used very often.

Typically implemented when we want to loop 

an undefined number of times

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