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Lección 8. Dictionary
Dificultad:
Tarea«Cálculo de unicidad»
💻 Python
Debes analizar los datos sobre los nombres que se les dan a los recién nacidos. Tienes un diccionario donde la clave es el nombre del niño (cadena), y el valor es la cantidad de veces que este nombre aparece en la lista de recién nacidos por año (un número entero). Tu tarea es determinar cuántos nombres diferentes (claves únicas) se usaron y cuál es el nombre más popular (el que aparece con mayor frecuencia). Si varios nombres tienen la misma máxima popularidad, muestra cualquiera de ellos.
Formato de entrada
Se introduce el diccionario, presentado por línea. Cada línea contiene el nombre y la cantidad separados por un espacio. La entrada termina con una línea vacía
Formato de salida
La primera línea toma el número de nombres únicos.
La segunda línea muestra el nombre más popular y el número de sus menciones, separados por un espacio.
Ejemplo
Entrada
Alexander 15
Maria 12
Ivan 15
Salida
3
Alexander 15
Pista
Useful methods for working with dictionaries in Python
Dictionaries are one of the most powerful and flexible data structures in Python. To use them effectively, it is important to know the basic methods. Let's take a closer look at them.
The keys() method
Returns all dictionary keys as a special representation object dict_keys.
my_dict = {'key1': 'value1', 'key2': 'value2', 'key3': 'value3'}
keys = my_dict.keys()
print(keys) # Output: dict_keys(['key1', 'key2', 'key3'])
A useful tip: The dict_keys object is iterable, meaning you can use it in a for loop. However, this is not a list. If you need a list of keys (for example, for index access), simply convert it using the list() function.
key_list = list(my_dict.keys())
print(key_list[0]) # Output: key1
The values() method
Returns all dictionary values as a representation object dict_values.
values = my_dict.values()
print(values) # Output: dict_values(['value1', 'value2', 'value3'])
A useful tip: Like dict_keys, dict_values can be iterated, but it is not a list. The conversion to list() also works if you need a list of values. This is convenient, for example, to check for the presence of a value.
The items() method
Returns all key-value pairs as a dict_items object, where each pair is represented as a tuple.
items = my_dict.items()
print(items) # Output: dict_items([('key1', 'value1'), ('key2', 'value2'), ('key3', 'value3')])
A useful tip: This method is incredibly convenient for iterating through a dictionary when you need both a key and a value at the same time. This is considered the most "Pythonic" way to bypass the dictionary.
for key, value in my_dict.items():
print(f"Key: {key}, Value: {value}")
get() method
Returns the value by key. If there is no key, it returns the default value (or None if it is not specified).
value = my_dict.get("key1")
print(value) # Output: value1
value_nonexistent = my_dict.get("key4", "there is no such key")
print(value_nonexistent) # Output: there is no such key
A useful tip: Use get() instead of direct access through square brackets (my_dict["key4"]) when you are not sure if the key exists in the dictionary. This will avoid the KeyError error and the crash of the program. This is much safer when working with data that comes from external sources.
The popitem() method
Deletes and returns the last added key-value pair as a tuple.
last_item = my_dict.popitem()
print(last_item) # Output: ('key3', 'value3')
print(my_dict) # Output: {'key1': 'value1', 'key2': 'value2'}
A useful tip: This method works according to the LIFO (Last-In, First-Out) principle. It is useful when you need to process dictionary elements in the reverse order of their addition. (Guaranteed LIFO order is supported in Python 3.7+).
The update() method
Updates the dictionary by adding key-value pairs from another dictionary or from an iterable object with pairs.
# The original my_dict dictionary is already without 'key3'
my_dict.update({"key4": "value4", "key1": "new value1"})
print(my_dict)
# Output: {'key1': 'new value1', 'key2': 'value2', 'key4': 'value4'}
A useful tip: Note that if the key from the updating dictionary already exists in the original one, its value will be overwritten. update() is an effective way to merge two dictionaries.
Nested dictionaries
Dictionaries can contain other dictionaries as values. This allows you to create complex hierarchical data structures very similar to the JSON format.
nested_dict = {
"key1": {"plugg1": "value1"},
"key2": {"plugg2": "value2"}
}
# Accessing the nested value
print(nested_dict["key1"]["plugg1"]) # Output: value1
An example of a multidimensional structure in dictionaries
students = {
"Alice": {"age": 25, "grades": [88, 92, 85]},
"Bob": {"age": 22, "grades": [79, 85, 80]},
"Charlie": {"age": 23, "grades": [90, 87, 85]}
}
# Getting Alice's age
print(students["Alice"]["age"]) # Output: 25
# Getting the first grade Bob
print(students["Bob"]["grades"][0]) # Output: 79
# Adding a new student
students["David"] = {"age": 24, "grades": [82, 79, 88]}
print(students)
A useful tip: When working with nested dictionaries, the risk of getting a KeyError increases. For secure access to the embedded data, you can use a chain of calls get().
# Safely obtaining the age of a student, which may not be
age = students.get("Eve", {}).get("age", "Unknown")
print(age) # Output: Unknown
Here students.get("Eve", {}) will return an empty dictionary {}, since there is no student "Eve", and already this empty dictionary will be called .get("age", ...), which will prevent the error.
main.py
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Solución del desarrollador
