0303 FreeCodeCamp Python Certification — Dictionaries and Sets Review

Dictionaries and Sets Review

📑Dictionary

Dictionaries are built-in data structures that store collections of key-value pairs.

dictionary = {
    key1: value1,
    key2: value2
}

To access the value of a key-value pair: dictionary[key]
The get() method retrieves the value associated with a key: dictionary.get(key, default)

The keys() and values() methods return a view object with all the keys and values in the dictionary, respectively.

pizza = {
  'name': 'Margherita Pizza',
  'price': 8.9,
  'calories_per_slice': 250
  }

 pizza.keys()
 # dict_keys(['name', 'price', 'calories_per_slice'])

 pizza.values()
 # dict_values(['Margherita Pizza', 8.9, 250])

The items() method returns a view object with all the key-value pairs in the dictionary, including both the keys and the values.
```
pizza.items()
# dict_items([('name', 'Margherita Pizza'), ('price', 8.9), ('calories_per_slice', 250)])
```

If you need to iterate over the values in a dictionary, you can write a for loop with values() to get all the values of a dictionary.

products = {
    'Laptop': 990,
    'Smartphone': 600,
    'Tablet': 250,
    'Headphones': 70,
}

for price in products.values():
    print(price)
# 990
  600
  250
  70

Iterating Over Keys: If you need to iterate over the keys in the products dictionary above, you can write products.keys() or products directly.
Iterating Over Key-Value Pairs: If you need to iterate over the keys and their corresponding values simultaneously, you can iterate over products.items().
enumerate() Function: If you need to iterate over a dictionary while keeping track of a counter, you can call the enumerate() function.

🧦Set

Sets are built-in data structures in Python that do not allow duplicate values.

Defining a Set: my_set = {1, 2, 3, 4, 5}
If you need to define an empty set, you must use the set() function.

The issubset() and the issuperset() methods check if a set is a subset or superset of another set, respectively.

my_set = {1, 2, 3, 4, 5}
your_set = {2, 3, 4, 5}

print(your_set.issubset(my_set)) # True
print(my_set.issuperset(your_set)) # True

The isdisjoint() method checks if two sets are disjoint, if they don’t have elements in common.

The union operator | returns a new set with all the elements from both sets.

my_set = {1, 2, 3}
your_set = {4, 5, 6}

my_set | your_set # {1, 2, 3, 4, 5, 6}

The intersection operator & returns a new set with only the elements that the sets have in common.
The difference operator - returns a new set with the elements of the first set that are not in the other sets.
The symmetric difference operator ^ returns a new set with the elements that are either in the first or the second set, but not both.
check if an element is in a set or not with the in operator: print(5 in my_set) # True

📚Python Standard Library

A library gives you pre-written and reusable code, like functions, classes, and data structures, that you can reuse in your projects.

use the import keyword followed by the name of the module: import module_name
if you need to call a method from that module, you would use dot notation, with the name of the module followed by the name of the method. module_name.method_name()
you can use as followed by the alias at the end of the import statement. import module_name as module_alias

Test　18/20

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