Lists, Dictionaries, Iteration

• Lists and Dictionaries
• List and Dictionary purpose
• Formatted output of List/Dictionary - for loop
• Alternate methods for iteration - while loop
• Calling a function repeatedly - recursion
• Hacks

Lists and Dictionaries

As a quick review we used variables in the introduction last week. Variables all have a type: String, Integer, Float, List and Dictionary are some key types. In Python, variables are given a type at assignment, Types are important to understand and will impact operations, as we saw when we were required to user str() function in concatenation.

1. Developers often think of variables as primitives or collections. Look at this example and see if you can see hypothesize the difference between a primitive and a collection.
2. Take a minute and see if you can reference other elements in the list or other keys in the dictionary. Show output.

# variable of type string
name = "Ellie"
print("name", name, type(name))

# variable of type integer
age = 14
print("age", age, type(age))

# variable of type float
score = 99.0
print("score", score, type(score))

print()

# variable of type list (many values in one variable)
langs = ["Python", "JavaScript", "Bash"]
print("langs", langs, type(langs))
print("- langs[1]", langs[1], type(langs[1]))

print()

# variable of type dictionary (a group of keys and values)
person = {
    "name": name,
    "age": age,
    "score": score,
    "langs": langs
}
print("person", person, type(person))
print('- person["name"]', person["name"], type(person["name"]))

name Ellie <class 'str'>
age 14 <class 'int'>
score 99.0 <class 'float'>

langs ['Python', 'JavaScript', 'Bash'] <class 'list'>
- langs[1] JavaScript <class 'str'>

person {'name': 'Ellie', 'age': 14, 'score': 99.0, 'langs': ['Python', 'JavaScript', 'Bash']} <class 'dict'>
- person["name"] Ellie <class 'str'>

List and Dictionary purpose

Our society is being build on information. List and Dictionaries are used to collect information. Mostly, when information is collected it is formed into patterns. As that pattern is established you will collect many instances of that pattern.

• List is used to collect many
• Dictionary is used to define data patterns.
• Iteration is often used to process through lists.

To start exploring more deeply into List, Dictionary and Iteration we will explore constructing a List of people and cars.

• As we learned above, List is a data type: class 'list'
• A 'list' data type has the method '.append(expression)' that allows you to add to the list
• In the example below, the expression appended to the 'list' is the data type: class 'dict'
• At the end, you see a fairly complicated data structure. This is a list of dictionaries. The output looks similar to JSON and we will see this often, you will be required to understand this data structure and understand the parts. Easy peasy ;).

InfoDb = []

# Append to List a Dictionary of key/values related to a person and cars
InfoDb.append({
    "FirstName": "John",
    "LastName": "Mortensen",
    "DOB": "October 21",
    "Residence": "San Diego",
    "Email": "jmortensen@powayusd.com",
<<<<<<< HEAD
    "Owns_Cars": ["2015-Fusion", "2011-Ranger", "2003-Excursion", "1997-F350", "1969-Cadillac"]
    "Favorite_Food": "unknown",
    "Owns_a_pet": "unknown"
=======
    "Owns_Cars": ["2015-Fusion", "2011-Ranger", "2003-Excursion", "1997-F350", "1969-Cadillac"],
    "Favorite_Food": "unknown",
    "Owns": "unknown"
>>>>>>> f44d76edc589c60593655631253fadb963713168
})

# Append to List a 2nd Dictionary of key/values
InfoDb.append({
    "FirstName": "Ellie",
    "LastName": "Pang",
    "DOB": "November 1",
    "Residence": "Del Sur",
    "Email": "elliepang007@gmail,com",
<<<<<<< HEAD
    "Owns_Cars": ["No"]
    "Favorite_Food": "Sushi",
    "Owns_a_Pet": "Yes"
    
=======
    "Owns_Cars": ["No"],
    "Favorite_Food": "Sushi",
    "Owns": "Yes"
>>>>>>> f44d76edc589c60593655631253fadb963713168
})

# Print the data structure
print(InfoDb)

<<<<<<< HEAD

  Input In [2]
    "Favorite_Food": "unknown",
    ^
SyntaxError: invalid syntax
=======

[{'FirstName': 'John', 'LastName': 'Mortensen', 'DOB': 'October 21', 'Residence': 'San Diego', 'Email': 'jmortensen@powayusd.com', 'Owns_Cars': ['2015-Fusion', '2011-Ranger', '2003-Excursion', '1997-F350', '1969-Cadillac'], 'Favorite_Food': 'unknown', 'Owns': 'unknown'}, {'FirstName': 'Ellie', 'LastName': 'Pang', 'DOB': 'November 1', 'Residence': 'Del Sur', 'Email': 'elliepang007@gmail,com', 'Owns_Cars': ['No'], 'Favorite_Food': 'Sushi', 'Owns': 'Yes'}]
>>>>>>> f44d76edc589c60593655631253fadb963713168


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Formatted output of List/Dictionary - for loop 

Managing data in Lists and Dictionaries is for the convenience of passing the data across the internet or preparing it to be stored into a database.  Also, it is a great way to exchange data inside of our own programs.
Next, we will take the stored data and output it within our notebook.  There are multiple steps to this process...


Preparing a function to format the data, the print_data() function receives a parameter called "d_rec" short for dictionary record.  It then references different keys within [] square brackets.   

Preparing a function to iterate through the list, the for_loop() function uses an enhanced for loop that pull record by record out of InfoDb until the list is empty.  Each time through the loop it call print_data(record), which passes the dictionary record to that function.
Finally, you need to activate your function with the call to the defined function for_loop().  Functions are defined, not activated until they are called.  By placing for_loop() at the left margin the function is activated.





    
    




    

def print_data(d_rec):
    print(d_rec["FirstName"], d_rec["LastName"])  # using comma puts space between values
    print("\t", "Residence:", d_rec["Residence"]) # \t is a tab indent
    print("\t", "Birth Day:", d_rec["DOB"])
    print("\t", "Cars: ", end="")  # end="" make sure no return occurs
    print(", ".join(d_rec["Owns_Cars"]))  # join allows printing a string list with separator
    print("\t", "Favorite_Food:", d_rec["Favorite_Food"])
<<<<<<< HEAD
    print("\t", "Owns_a_Pet:", d_rec["Pet_Owner"]) 
=======
    print("\t", "Pet Owner:", d_rec["Owns"]) 
>>>>>>> f44d76edc589c60593655631253fadb963713168
    


# for loop iterates on length of InfoDb
def for_loop():
    print("For loop output\n")
    for record in InfoDb:
        print_data(record)

for_loop()


    









For loop output

John Mortensen
	 Residence: San Diego
	 Birth Day: October 21
	 Cars: 2015-Fusion, 2011-Ranger, 2003-Excursion, 1997-F350, 1969-Cadillac
<<<<<<< HEAD
=======
	 Favorite_Food: unknown
	 Pet Owner: unknown
Ellie Pang
	 Residence: Del Sur
	 Birth Day: November 1
	 Cars: No
	 Favorite_Food: Sushi
	 Pet Owner: Yes
>>>>>>> f44d76edc589c60593655631253fadb963713168




<<<<<<< HEAD



---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb Cell 7 in <cell line: 19>()
     <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#W6sdnNjb2RlLXJlbW90ZQ%3D%3D?line=15'>16</a>     for record in InfoDb:
     <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#W6sdnNjb2RlLXJlbW90ZQ%3D%3D?line=16'>17</a>         print_data(record)
---> <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#W6sdnNjb2RlLXJlbW90ZQ%3D%3D?line=18'>19</a> for_loop()

/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb Cell 7 in for_loop()
     <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#W6sdnNjb2RlLXJlbW90ZQ%3D%3D?line=14'>15</a> print("For loop output\n")
     <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#W6sdnNjb2RlLXJlbW90ZQ%3D%3D?line=15'>16</a> for record in InfoDb:
---> <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#W6sdnNjb2RlLXJlbW90ZQ%3D%3D?line=16'>17</a>     print_data(record)

/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb Cell 7 in print_data(d_rec)
      <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#W6sdnNjb2RlLXJlbW90ZQ%3D%3D?line=5'>6</a> print("\t", "Cars: ", end="")  # end="" make sure no return occurs
      <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#W6sdnNjb2RlLXJlbW90ZQ%3D%3D?line=6'>7</a> print(", ".join(d_rec["Owns_Cars"]))  # join allows printing a string list with separator
----> <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#W6sdnNjb2RlLXJlbW90ZQ%3D%3D?line=7'>8</a> print("\t", "Favorite_Food:", d_rec["Favorite_Food"])
      <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#W6sdnNjb2RlLXJlbW90ZQ%3D%3D?line=8'>9</a> print("\t", "Owns_a_Pet:", d_rec["Pet_Owner"])

KeyError: 'Favorite_Food'



=======
>>>>>>> f44d76edc589c60593655631253fadb963713168




    





Alternate methods for iteration - while loop 

In coding, there are usually many ways to achieve the same result.  Defined are functions illustrating using index to reference records in a list, these methods are called a "while" loop and "recursion".

The while_loop() function contains a while loop, "while i < len(InfoDb):".  This counts through the elements in the list start at zero, and passes the record to print_data()





    
    




    

def while_loop():
    print("While loop output\n")
    i = 0
    while i < len(InfoDb):
        record = InfoDb[i]
        print_data(record)
        i += 1
    return

while_loop()


    









While loop output

John Mortensen
	 Residence: San Diego
	 Birth Day: October 21
	 Cars: 2015-Fusion, 2011-Ranger, 2003-Excursion, 1997-F350, 1969-Cadillac
<<<<<<< HEAD
=======
	 Favorite_Food: unknown
	 Pet Owner: unknown
Ellie Pang
	 Residence: Del Sur
	 Birth Day: November 1
	 Cars: No
	 Favorite_Food: Sushi
	 Pet Owner: Yes
>>>>>>> f44d76edc589c60593655631253fadb963713168




<<<<<<< HEAD



---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb Cell 9 in <cell line: 11>()
      <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#X11sdnNjb2RlLXJlbW90ZQ%3D%3D?line=7'>8</a>         i += 1
      <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#X11sdnNjb2RlLXJlbW90ZQ%3D%3D?line=8'>9</a>     return
---> <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#X11sdnNjb2RlLXJlbW90ZQ%3D%3D?line=10'>11</a> while_loop()

/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb Cell 9 in while_loop()
      <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#X11sdnNjb2RlLXJlbW90ZQ%3D%3D?line=4'>5</a> while i < len(InfoDb):
      <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#X11sdnNjb2RlLXJlbW90ZQ%3D%3D?line=5'>6</a>     record = InfoDb[i]
----> <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#X11sdnNjb2RlLXJlbW90ZQ%3D%3D?line=6'>7</a>     print_data(record)
      <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#X11sdnNjb2RlLXJlbW90ZQ%3D%3D?line=7'>8</a>     i += 1
      <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#X11sdnNjb2RlLXJlbW90ZQ%3D%3D?line=8'>9</a> return

/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb Cell 9 in print_data(d_rec)
      <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#X11sdnNjb2RlLXJlbW90ZQ%3D%3D?line=5'>6</a> print("\t", "Cars: ", end="")  # end="" make sure no return occurs
      <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#X11sdnNjb2RlLXJlbW90ZQ%3D%3D?line=6'>7</a> print(", ".join(d_rec["Owns_Cars"]))  # join allows printing a string list with separator
----> <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#X11sdnNjb2RlLXJlbW90ZQ%3D%3D?line=7'>8</a> print("\t", "Favorite_Food:", d_rec["Favorite_Food"])
      <a href='vscode-notebook-cell://wsl%2Bubuntu/home/elliepang007/elliepang/_notebooks/2022-08-29-TP120-python_lists.ipynb#X11sdnNjb2RlLXJlbW90ZQ%3D%3D?line=8'>9</a> print("\t", "Owns_a_Pet:", d_rec["Pet_Owner"])

KeyError: 'Favorite_Food'



=======
>>>>>>> f44d76edc589c60593655631253fadb963713168




    





Calling a function repeatedly - recursion 

This final technique achieves looping by calling itself repeatedly.

recursive_loop(i) function is primed with the value 0 on its activation with "recursive_loop(0)"
the last statement indented inside the if statement "recursive_loop(i + 1)" activates another call to the recursive_loop(i) function, each time i is increasing
ultimately the "if i < len(InfoDb):" will evaluate to false and the program ends





    
    




    

def recursive_loop(i):
    if i < len(InfoDb):
        record = InfoDb[i]
        print_data(record)
        recursive_loop(i + 1)
    return
    
print("Recursive loop output\n")
recursive_loop(0)


    









Recursive loop output

John Mortensen
	 Residence: San Diego
	 Birth Day: October 21
	 Cars: 2015-Fusion, 2011-Ranger, 2003-Excursion, 1997-F350, 1969-Cadillac
<<<<<<< HEAD

=======
	 Favorite_Food: unknown
	 Pet Owner: unknown
>>>>>>> f44d76edc589c60593655631253fadb963713168
Ellie Pang
	 Residence: Del Sur
	 Birth Day: November 1
	 Cars: No
<<<<<<< HEAD

=======
	 Favorite_Food: Sushi
	 Pet Owner: Yes








    

    
    




    

food = ["pasta", "pizza", "strawberries", "chips", "french fries", "cherries"]
# while loop contains an initial n and an index incrementing statement (n += 1)
def while_loop():
    print("While loop output\n")
    i = 0
    while i < len(food):
        print(food[i])
        i += 1
    return

while_loop()


    









While loop output

pasta
pizza
strawberries
chips
french fries
cherries








    

    
    




    

def while_loop():
    print("While loop output\n")
    i = 5
    while i >=0:
        print(food[i])
        
        i -= 1
    return

while_loop()


    









While loop output

cherries
french fries
chips
strawberries
pizza
pasta








    

    
    




    

food = ["pasta", "pizza", "strawberries", "chips", "french fries", "cherries"]

def while_loop():
    print("While loop output\n")
    i=0
    while i<len(food):
        print(food[i])
        i +=1
    return 

while_loop()

def while_loop():
    print("While loop output\n")
    i=4
    while i >=0:
        print(food[i])
        i -=1
    return

while_loop()

for index, val in enumerate(food):
    print(index, val)


    









While loop output

pasta
pizza
strawberries
chips
french fries
cherries
While loop output

french fries
chips
strawberries
pizza
pasta
0 pasta
1 pizza
2 strawberries
3 chips
4 french fries
5 cherries








    

    
    




    

import getpass, sys

FoodQuestion = ["Fruit", "Vegetable", "Soup", "Drink", "Snack"]
FoodAnswer = ["Apple", "Carrot", "Clam Chowder", "Milkshake", "Chips"]
# Lists (ignore these they aren't used in the code)
Food = {
    "Fruit": "Apple",
    "Vegetable": "Carrot",
    "Soup": "Clam Chowder",
    "Drink": "Milkshake",
    "Snack": "Chips",
}
# The dictionary/list dictionary

CorrectList = {}
IncorrectList = {}
# Empty dictionaries used to store data

def question_with_response(question):
    print("What is my favorite " + question + "?")
    msg = input ()
    return msg

# defines and prints question; asks for input

def question():
    for question in FoodQuestion:
        rsp = question_with_response(question)
        if (rsp != Food [question]):
            print (rsp + " is incorrect.")
            IncorrectList [question] = rsp
        else:
            print (rsp + " is correct.")
            CorrectList [question] = rsp

# defines unit as one of the keys in the dictionary
# answers are marked as incorrect if they do not match the values that go with the keys
        
question()


    









What is my favorite Fruit?
 is incorrect.
What is my favorite Vegetable?
 is incorrect.
What is my favorite Soup?
 is incorrect.
What is my favorite Drink?
 is incorrect.
What is my favorite Snack?
 is incorrect.
>>>>>>> f44d76edc589c60593655631253fadb963713168








    





Hacks 


Add a couple of records to the InfoDb
Try to do a for loop with an index
Pair Share code somethings creative or unique, with loops and data. Hints...

Would it be possible to output data in a reverse order?
Are there other methods that can be performed on lists?
Could you create new or add to dictionary data set?  Could you do it with input?
Make a quiz that stores in a List of Dictionaries.







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