data2.py

# Pre-req's : loops, conditionals, functions, lists, tuples, and dictionaries
#
# Python 2.7
#
# Objectives : Advanced dictionaries, handling key collisions

# Remember in the previous lesson, we defined a contact record using the following tuple

contact = ('first_name','last_name','mobile_phone','home_phone','zip_code')

FIRST_NAME = 0 # First name is in the first position of the tuple.
LAST_NAME = 1 # Last name i sin the second position of the tuple...
MOBILE_PHONE = 2
HOME_PHONE = 3
ZIP_CODE = 4

# We built a simple function to help us create contact tuples

def create_contact(first_name,last_name,mobile_phone,home_phone=None,zip_code=None):
    return (first_name,last_name,mobile_phone,home_phone,zip_code)


# And we had some concerns about how to handle contacts with the same first or last name.
# So, we'll add some contacts with name overlaps:

contacts = []
contacts.append(create_contact("Sue","Simmons","804-555-1234"))
contacts.append(create_contact("John","Doe","804-555-1235","804-555-1236"))
contacts.append(create_contact("Pat","Petri","804-555-1237","804-555-1238","23117"))
contacts.append(create_contact("John","Smith","804-555-4321","804-555-4322"))
contacts.append(create_contact("Steve","Simmons","804-555-4323","804-555-4323","23117"))

# We know we want to create separate dictionaries to help us find by first name or last name.
# We'll want to create a function that keeps our dictionaries in sync. Thus, we really only need
# to think about how to deal with what to return when one searches for first name using "John".
# Remember, a Python dictionary doesn't reall "care" what you are putting in the dictionary.
# If we know there could be more than 1 contacts with the same first name, why not store a list
# of contacts by first name? Right?? Make sense? Let's look at the code:

contacts_by_first_name = {}

# The "trick" is that this dictionary will store a list of contacts as its value.
# In other words, the structure will be like this: { first_name2: [contact1, contact2, ...], ... }

for contact in contacts:
    # We want to see if there is already an entry for the key
    first_name = contact[FIRST_NAME]
    if first_name in contacts_by_first_name.keys():
        contacts_by_first_name[first_name].append(contact)
    else:
        contacts_by_first_name[first_name] = [contact]

    # Follow that?
    # Essentially, if there is already a contact in the dictionary, append the other one with the
    # same key to the list of contacts with that same key.
    # If there isn't a contact there, create a list with just the one contact.

# let's look at what the dictionary looks like:

print
print "A dictionary (index) that handles key collisions, by storing the list of matching contacts in the value."
print contacts_by_first_name

# So, now, the find by first_name will return a list of results, which is exactly what one would expectx!

contact = contacts_by_first_name["John"]

print
print "Find by first_name 'John'"
print contact

# This is pretty neat, right? Python doesn't care what the value is... a tuple, a string, or, in
# this case, a list of tuples! Wait 'til we discuss dictionaries of dictionaries (of dictionaries)...

# Can you write the code for contacts_by_last_name?
contacts_by_last_name = {}

# Let's look at the code for the add_contact method now:

def add_contact(contact):
    first_name = contact[FIRST_NAME]
    if first_name in contacts_by_first_name.keys():
        contacts_by_first_name[first_name].append(contact)
    else:
        contacts_by_first_name[first_name] = [contact]

    last_name = contact[LAST_NAME]
    if last_name in contacts_by_last_name.keys():
        contacts_by_last_name[last_name].append(contact)
    else:
        contacts_by_last_name[last_name] = [contact]

add_contact(create_contact("Bart","Simpson","804-555-4321"))
        
print
print "What do your dictionaries look like now?"
print contacts_by_first_name
print contacts_by_last_name