- 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
- Calling a for loop with index
- Outputting data in reverse
- Poping and Slicing from a List
- Adding to a Dictionary with Inputs
- Quiz using Dictionaries
- Hacks
Lists and Dictionaries
As a quick review of variables in the introduction last week. String, Integer, Float, List and Dictionary are some of the types of variables. 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.
- 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.
- 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 = "John Doe"
print("name", name, type(name)) #string is a primitive
# variable of type integer
age = 18
print("age", age, type(age)) #int is a primitive
# variable of type float
score = 90.0
print("score", score, type(score)) #float is a primitive
print()
# variable of type list (many values in one variable)
langs = ["Python", "JavaScript", "Java"]
print("langs", langs, type(langs)) #list is a collection
print("- langs[0]", langs[0], type(langs[0])) #element in this list in a primitive
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)) #dictionary is a collection
print('- person["name"]', person["name"], type(person["name"])) #string in dictionary is primitive
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",
"Owns_Cars": ["2015-Fusion", "2011-Ranger", "2003-Excursion", "1997-F350", "1969-Cadillac"]
})
# Append to List a 2nd Dictionary of key/values
InfoDb.append({
"FirstName": "Sunny",
"LastName": "Naidu",
"DOB": "August 2",
"Residence": "Temecula",
"Email": "snaidu@powayusd.com",
"Owns_Cars": ["4Runner"]
})
InfoDb.append({
"FirstName": "Haoxuan",
"LastName": "Tong",
"DOB": "July 9",
"Residence": "San Diego",
"Email": "haoxuantong8@gmail.com",
"Owns_Cars": []
})
# Print the data structure
print(InfoDb)
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()
# for loop iterates on length of InfoDb
def for_loop():
print("For loop output\n")
for record in InfoDb:
print_data(record)
InfoDb = []
InfoDb.append({
"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"]
})
InfoDb.append({
"FirstName": "Sunny",
"LastName": "Naidu",
"DOB": "August 2",
"Residence": "Temecula",
"Email": "snaidu@powayusd.com",
"Owns_Cars": ["4Runner"]
})
InfoDb.append({
"FirstName": "Haoxuan",
"LastName": "Tong",
"DOB": "July 9",
"Residence": "San Diego",
"Email": "haoxuantong8@gmail.com",
"Owns_Cars": []
})
for_loop()
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()
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)
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()
# for loop iterates on length of InfoDb
def for_loop():
print("For loop output\n")
for i in range(len(InfoDb)): #Using range(len(InfoDb)) to create an iterable of indices
print_data(InfoDb[i])
for_loop()
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()
# for loop iterates on length of InfoDb with indices
def for_loop_indices():
print("Reverse with indices\n")
for i in range(len(InfoDb)-1,-1,-1): #Using range(len(InfoDb)-1,-1,-1) to create a reversed iterable of indices
print_data(InfoDb[i])
for_loop_indices()
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()
# for loop iterates on length of InfoDb
def for_loop():
print("For loop output\n")
for i in range(len(InfoDb)): #Using range(len(InfoDb)) to create an iterable of indices
print_data(InfoDb[i])
print("pop")
print("Original List\n")
for_loop()#printing the original list
popped=InfoDb.pop(0)#popping the first element from list and storing it in a variable
print("New List\n")
for_loop()#printing the new list
print("Popped Variable\n")
print_data(popped)#printing the popped variable
InfoDb.append(popped)#adding the popped element back into the list
print("")
print("slice")
print("Original List\n")
for_loop()#printing the original list
aSlice=InfoDb[1:3]#slicing the second element and third from list and storing it in a variable
print("New List\n")
for_loop()#printing the new list, it should be the same
print("Slice variables")
print_data(aSlice[0])#printing the first and second variable in the slice
print_data(aSlice[1])
print("")
aDict={
'a':12,
'b':34
}#creating a dictionary
print("Original Dictionary")
print(aDict)
key=input("Enter your key (str): ")#get the key
ele=int(input("Enter your element (int): "))#get the element
aDict[key]=ele#adding the element to the dictionary
print("New Dictionary")
print(aDict)#printing the dictionary
import getpass, sys
def question_with_response(prompt):
#function for asking and answering
print("Question: " + prompt)
msg = input()
return msg
quizQnA={
"What folder is used to create markdown posts?":"posts",
"What folder is used to create notebook posts?":"notebook",
"What is the term for submitting a change made in editor?":"commit",
"What command is used to include other functions that are developed?":"import",
"What command in this example is used to evaluate a response?":"if",
"Each 'if' command contains an '_________' to determine a true or false condition?":"expression",
}#define the questions
quizLength=len(quizQnA)#measures the length of question
ans=0#add variable for answered correctly
for question in quizQnA:
resp=question_with_response(question)
if resp==quizQnA[question]:
print(resp+" was correct!")
ans+=1
else:
print(resp+" was incorrect.")
print("The correct answer is "+quizQnA[question])
print(getpass.getuser()+", you scored "+str(ans)+"/"+str(quizLength)+", which is "+str(format(ans/quizLength*100,".2f"))+"%")
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.