3
Voymir Levtolstoy 10 300.00
Crime announcement Fedordostoevsky 5 450.50
Masters Mikhailbulgakov 7 400.00
The most popular book: Voymir
Author with the greatest revenue: Levtolstoy
Average price: 368.58
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.
EN
RU
EN
RU
keys() methodReturns 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
values() methodReturns 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.
items() methodReturns 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() methodReturns 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.
popitem() methodDeletes 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+).
update() methodUpdates 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.
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
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.
1 - Read the task and understand what needs to be done
2 - The example shows how the input data will be provided and what output is expected
3 - Write the code considering the input, output, and the task itself.
1 - The “Run” button executes your code only on one set of input data, and you’ll see the result in the output window.
2 - The “Test on All Cases” button runs your code against all test cases. If all tests pass, a banner will appear. If even one test fails, it will be highlighted in red.
To change the input data, click the “Run Test” button next to the input data you want to execute.
1 - Input Data is the window containing the values loaded into your program in place of input()
2 - Program Output is the window showing what your program prints. If it’s green, the output matches the expected result; if red, there are differences.
3 - Expected Output is the reference value used to verify the solution.
1 - Green means the program produced the correct output
2 - Red means the program’s output didn’t match the expected output for this data. The program output and the expected output must be identical, including spaces and punctuation!
If you see this banner, congratulations — everything is correct.
1 - The first 10 tasks are quite easy and contain hints covering only the essential parts of the topic.
2 - The next 10 tasks are medium difficulty. Their hints differ from the easy ones and reveal new aspects of the topic.
3 - The hardest tasks have no hints. Often, they include additional topics, so sometimes it’s better to move on and return later. Read the hints carefully — they offer new ways to solve already familiar problems.
1 - Each block contains a “Theory” section.
2 - It always includes a detailed video.
3 - There is also a detailed guide with all the necessary theory and code examples.
1 - Click the “Report an Error / Social Media” button
2 - Here you can describe the error you encountered.
3 - You’ll also find our social media links here — follow us and help us improve.
🎉 Congratulations! 🎉
You did an excellent job with the task! It was a challenging problem, but you found the correct solution. You are one step closer to mastering programming! Keep up the good work, because every stage you pass makes you even stronger.
AD
Advertisement
Running your code...