Dictionary
It’s a fundamental data structure in python, are mutable and we can always add new items after the dictionary has been created.
The dict() function creates a dictionary.
Here we will use a dictionary to create a simple phone book. You can create,add new names or modify existing ones.
Example:
phone_book= {'Mary': '642-534-678','Carlos':'623-678-903', 'Eli': '610-678-234'}
print(phone_book)
output:
{'Mary': '642-534-678', 'Carlos': '623-678-903', 'Eli': '610-678-234'}
Other way to do it is in different lines, in my opinion this is a more comfortable way because you can see better the details.
Example:
phone_book= {
'Mary': '642-534-678',
'Carlos':'623-678-903',
'Eli': '610-678-234'
}
print(phone_directory)
Adding new items in a Dictionary
Adding an item to the dictionary is done by using a new key and assigning a value to it.
Example:
phone_book= {'Mary': '642-534-678','Carlos':'623-678-903', 'Eli': '610-678-234'}
# Add new item
phone_book['Louis'] = '612-987-564'
print(phone_book)
Output:
You can see as a result how the new item “louis” was added to the phone book:
{'Mary': '642-534-678', 'Carlos': '623-678-903', 'Eli': '610-678-234', 'Louis': '612-987-564'}
Change Values in a Dictionary
You can change the value of a specific item using the same key name.
Example:
phone_book= {'Mary': '642-534-678','Carlos':'623-678-903', 'Eli': '610-678-234'}
#Replace item
phone_book['Mary']= '988-034-567'
print(phone_book)
Output:
You can se how the item “mary” was replaced for the new number:
{'Mary': '988-034-567', 'Carlos': '623-678-903', 'Eli': '610-678-234', 'Louis': '612-987-564'}
Duplication Not Allowed
Dictionaries cannot have two items with the same key because the duplicate values will overwrite existing values.
Example:
objet= {"Price": "3$", "Name":"pen", "Color":"Black", "Color":"Blue" }
print(objet)
Here i’m using a keyword already defined as a result these will be replaced and not added as new:
Output:
{'Price': '3$', 'Name': 'pen', 'Color': 'Blue'}
Dictionary Length
To determine how many items a dictionary has, use the len() function.
Example:
objet= {"Price": "3$", "Name":"pen", "Color":"Black" }
print(len(objet))
# Output
3
Update Dictionary
The update() function insert items to the dictionary. This items can be a dictionary, or an object. The function it’s similar to add new item.
Example:
dict = {
"p" : "potato",
"s" : "strawberry",
"g" : "grapes",
"a" : "avocado"
}
dict.update({"t": "tomato", "b": "banana"})
print(dict)
Output:
{'p': 'potato', 's': 'strawberry', 'g': 'grapes', 'a': 'avocado', 't': 'tomato', 'b': 'banana'}
Copy a dictionary
With this function we can copy an existing dictionary. This is the function copy().
Example:
dict = {
"p" : "potato",
"s" : "strawberry",
"g" : "grapes",
"a" : "avocado"
}
food = dict.copy()
print(food)
Check if Key Exists in Dictionary
When you want to determine if a specified key is present in a dictionary you can use the in keyword.
Example:
dict = {
"Letter p" : "potato",
"Letter s" : "strawberry",
"Letter g" : "grapes",
"Letter a" : "avocado"
}
if "Letter a" in dict:
print("Yes, 'Letter a' is in dict! ")
Output:
Yes, 'Letter a' is in dict!
Loop Through a Dictionary
You can loop through a dictionary by using a for loop.
For loop
Print all key names in the dictionary, one by one with the function for ... in ..
Example:
dict = {
"Letter p" : "potato",
"Letter s" : "strawberry",
"Letter g" : "grapes",
"Letter a" : "avocado"
}
for dict in dict:
print(dict)
Output:
Letter p
Letter s
Letter g
Letter a
Value function
We can use this function values() to return values of a dictionary.
Example:
dict = {
"Letter p" : "potato",
"Letter s" : "strawberry",
"Letter g" : "grapes",
"Letter a" : "avocado"
}
for dict in dict.values():
print(dict)
Output:
potato
strawberry
grapes
avocado
Items function
To have both,keys and values, use the items() function.
Example:
dict = {
"Letter p" : "potato",
"Letter s" : "strawberry",
"Letter g" : "grapes",
"Letter a" : "avocado"
}
for dict in dict.items():
print(dict)
Output:
('Letter p', 'potato')
('Letter s', 'strawberry')
('Letter g', 'grapes')
('Letter a', 'avocado')
Nested Dictionaries
This mean that the dictionary contain many dictionaries. Example, we are going to create a dictionary that contain 3 dictionaries.
Example:
my_pets= {
"pet1" : {
"name" : "choky",
"year" : 2016
},
"pet2" : {
"name" : "cate",
"year" : 2018
},
"pet3" : {
"name" : "micky",
"year" : 2019
}
}
print(my_pets)
Output:
{'pet1': {'name': 'choky', 'year': 2016}, 'pet2': {'name': 'cate', 'year': 2018}, 'pet3': {'name': 'micky', 'year': 2019}}
Remove items from a dictionary
Not only we can modify the items, we can also remove characters from the dictionary that we don’t want. There are several methods to do it:
Pop function
The pop() method removes the item with the specified key name.
Example:
dict = {
"p" : "potato",
"s" : "strawberry",
"g" : "grapes",
"a" : "avocado"
}
dict.pop ("g")
print(dict)
Output:
{'p': 'potato', 's': 'strawberry', 'a': 'avocado'}
Pop item function
The popitem() method removes the last inserted item (in versions before 3.7, a random item is removed instead).
Example:
dict = {
"p" : "potato",
"s" : "strawberry",
"g" : "grapes",
"a" : "avocado"
}
dict.popitem()
print(dict)
Output:
{'p': 'potato', 's': 'strawberry', 'g': 'grapes'}
Del function
The del keyword removes the item with the specified key name.
Example:
dict = {
"p" : "potato",
"s" : "strawberry",
"g" : "grapes",
"a" : "avocado"
}
del dict["p"]
print(dict)
Output:
{'s': 'strawberry', 'g': 'grapes', 'a': 'avocado'}
This function can also delete the dictionary completely.
This will cause an error because “dict” no longer exists.
Example:
dict = {
"p" : "potato",
"s" : "strawberry",
"g" : "grapes",
"a" : "avocado"
}
del dict
print(dict)
Clear
The clear() keyword is used to empty the dictionary.
Example:
dict = {
"p" : "potato",
"s" : "strawberry",
"g" : "grapes",
"a" : "avocado"
}
dict.clear()
print(dict)
#Output
{}