Day15

Day 15: Dictionaries

Instructions:

1. Open a new python file.
2. Dictionaries are extremely useful objects that allow the user to map values to a specific key. These values can be returned simply by calling the key. This makes dictionaries not only useful, but also efficient. A dictionary is declared by using curly brackets ({}) and separating the key from the value with a colon (:). In order to call the value, the key is referenced in square brackets ([]) appended to the name of the dictionary.

   conversion = {"a": 1, "b": 2, "c": 3, "d": 4, "e": 5}
   print(conversion)
   print(conversion["a"])
   

3. Dictionaries require the key to be a single item, but the value can be a list of multiple items.

   menu = {"item1": ["egg", "spam", "bacon"],
           "item2": ["egg", "sausage", "spam"],
           "item3": ["egg", "spam"],
           "item4": ["egg", "bacon", "spam"],
           "item5": ["egg", "bacon", "sausage", "spam"],
           "item6": ["spam", "bacon", "sausage", "spam"],
           "item7": ["spam", "egg", "spam", "spam", "bacon", "spam"],
           "item8": ["spam", "egg", "sausage", "spam"]}
   print(menu["item1"])
   print(type(menu["item7"]
   

4. Since the value in the menu dictionary is a list, it can be changed in the same methodology as a normal list. By using slicing in conjunction with the key, specific items in the list can be retrieved and modified.

   menu["item2"][2] = "spam"
   print(menu["item2"])
   

5. Lists are ordered collections of content, but dictionaries are not. In a dictionary, the key/value pairs can be added in any order. As long as the key/value pairs match between two dictionaries, python will interpret both to be the same.

   # List Comparison
   l_ministry1 = ["silly", "walks"]
   l_ministry2 = ["walks", "silly"]
   l_ministry1 == l_ministry2
   
   # Dictionary Comparison
   d_ministry1 = {"a": "silly", "b": "walks"}
   d_ministry2 = {"b": "walks", "a": "silly"}
   d_ministry1 == d_ministry2
   

6. The keys and values of the dictionary can be called using the keys() and values() methods.

   print(menu.keys())
   print(menu.values())
   

7. A dictionary can be sorted by using the keys() or values() method and converting the output to a list. This list can be sorted and displayed for the user. Type and execute:

   ordered_keys = list(menu.keys())
   print(ordered_keys)
   ordered_keys.sort(reverse=True)
   print(ordered_keys)
   

8. By using the tuple() function, a dictionary can be converted into a tuple. Each item in the tuple will be a tuple as well. This is how python handles the key/value pairs in a format that does not technically support that functionality. Since this key/value pair is a tuple, slicing can be applied to the sliced item to obtain the key or value. Additionally, slicing can be applied to the sliced value, from the sliced tuple, to obtain a specific item in the list.

   menu_tuple = tuple(menu.items())
   print(menu_tuple)
   print(type(menu_tuple))
   print(menu_tuple[0])
   print(type(menu_tuple[0]))
   
   # Slicing the key/value tuple to obtain the key.
   print(menu_tuple[0][0])
   print(type(menu_tuple[0][0]))
   
   # Slicing the key/value tuple to obtain the value.
   print(menu_tuple[0][1])
   print(type(menu_tuple[0][1]))
   
   # Slicing the second item in the value list.
   print(menu_tuple[0][1][1])
   print(type(menu_tuple[0][1][1]))
   

9. Instead of implementing triple slicing to get some spam, let's use the dictionary to obtain the same result.

   print(menu["item1"][1])
   print(menu_tuple[0][1][1] == menu["item1"][1])
   

10. The get() method is a way to retrieve a value from a key, but also contain a default value if no key is found.

order = "item6"
if menu.get(order, 0) == 0:
    print("{} is not a valid dish. Please try again.".format(order))
else:
    print("{} contains {}".format(order, menu.get(order)))

11. The setdefault() method is used to create a default key/value combination for a dictionary. This is useful for applications where verbose data is required, but all of the information is not available. If the dictionary already contains a key by the default's name, the value is not changed by the default.

transportation = {"name": "coconut", "color": "brown"}
print(transportation.items())
transportation.setdefault("received_by", "swallow")
print(transportation.items())
transportation.setdefault("received_by", "found_on_ground")
print(transportation.items())

12. Update the log file with what you have learned today.