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Lektion 8. Dictionary
Schwierigkeit:
Aufgabe«Abschluss der Schlüssel»
💻 Python
Sie arbeiten als Analyst in einem kleinen Geschäft. Sie haben Informationen über die pro Tag getätigten Einkäufe. Jeder Einkauf wird in Form eines Wörterbuchs dargestellt, wobei der Schlüssel der Name des Artikels und der Wert die Anzahl der gekauften Einheiten dieses Artikels ist. Sie müssen eine gemeinsame Liste der Einkäufe erstellen und die Gesamtanzahl jeder pro Tag verkauften Position berechnen.
Eingabeformat
Zuerst wird die ganze Zahl
Dann werden
n – Die Anzahl der an diesem Tag registrierten Einkäufe eingegeben. Dann werden
n mal die Daten zu jedem Einkauf eingegeben. Jeder Einkauf wird im folgenden Format eingegeben: Zuerst die ganze Zahl
m – Die Anzahl der verschiedenen Waren in diesem Einkauf. Dann werden
m mal der Name des Produkts (Zeile) und die Anzahl der gekauften Einheiten dieses Produkts (ganze Zahl) durch ein Leerzeichen getrennt eingegeben. Ausgabeformat
Geben Sie die Gesamtliste der Waren und die Gesamtanzahl der verkauften Einheiten jedes Produkts aus. Jedes Produkt muss in einer separaten Zeile im Format:
"Anzahl Name" angezeigt werden. Die Produkte sollten in lexikografischer Reihenfolge nach dem Warennamen sortiert werden. Beispiel
Eingabe
2
3
Apple 2
Milk 1
Bread 1
2
Apple 1
Cheese 1
Ausgabe
Milch 1
Käse 1
Brot 1
Apfel 3
Hinweis
Dictionaries in python
Dictionaries in Python are a powerful and indispensable data structure that allows you to store information in the form of key-value pairs. Imagine a real dictionary or phone book: knowing a unique word (key), you instantly find its definition (meaning). Dictionaries simplify organization and, most importantly, provide very fast access to data based on unique keys.
The main characteristics of dictionaries
- The keys are unique: Each key in the dictionary must be unique. Trying to add a key that already exists will simply overwrite its value.
- Changeability: Dictionaries are mutable objects. You can add, modify, and delete key-value pairs after creating a dictionary.
- Disorder (historically): In older versions of Python (before 3.7), dictionaries were considered unordered. However, starting with Python 3.7, they preserve the order in which elements are inserted. You should be careful to rely on this order if your code is supposed to run on older versions.
A useful tip: Only immutable data types such as strings, numbers, or tuples can be used as keys. Lists or other dictionaries cannot be keys, as they can be changed. But you can use absolutely any data type as values: numbers, strings, lists, and even other dictionaries.
Ways to create dictionaries
Dictionaries can be created in several ways:
1. Empty dictionary
my_dict = {}
# or using the built-in function
my_dict = dict()
2. Dictionary with elements (literal method) This is the most common and readable way.
user_profile = {
"username": "alex",
"level": 15,
"items": ["sword", "shield", "potion"]
}
3. Using the dict function with named arguments This method is convenient for simple dictionaries where the keys are strings.
my_dict = dict(key1="value1", key2="value2")
4. Creating tuples (pairs) from a list This method is useful when the data is received as a list of pairs.
pairs = [('a', 1), ('b', 2), ('c', 3)]
my_dict = dict(pairs)
# Result: {'a': 1, 'b': 2, 'c': 3}
Access to the elements
Dictionary values are accessed through their keys in square brackets.
my_dict = {"key1": "value1", "key2": "value2"}
print(my_dict["key1"]) # Output: value1
An important point: If you try to access a key that does not exist, Python will cause a KeyError error. To avoid this, use the .get() method.
Secure access using the .get() method The .get() method returns None if the key is not found and does not cause an error. You can also pass the second argument the default value, which will be returned instead of None.
print(my_dict.get("key3")) # Output: None
print(my_dict.get("key3", "not found")) # Conclusion: not found
Changing and adding elements
Adding or changing elements is very simple:
my_dict = {"key1": "old value"}
# Changing an existing element
my_dict["key1"] = "new value"
print(my_dict["key1"]) # Output: new value
# Adding a new element
my_dict["key3"] = "value3"
print(my_dict) # Output: {'key1': 'new value', 'key3': 'value3'}
To combine dictionaries, you can use the .update() method:
dict1 = {'a': 1, 'b': 2}
dict2 = {'b': 3, 'c': 4}
dict1.update(dict2) # Key 'b' will be overwritten, 'c' will be added
print(dict1) # Output: {'a': 1, 'b':3, 'c':4}
Deleting elements
There are several ways to delete items in dictionaries.:
- Using the
del operatorDeletes a key pair. Causes aKeyErrorerror if the key is not found.del my_dict["key1"] - Using the
.pop() methodDeletes an element by key and returns its value. This is useful if you need to use a deleted value. If the key is not found, it will cause aKeyError, but you can pass the default value.my_dict = {'key2': 'value2', 'key3': 'value3'} value = my_dict.pop("key2") print(value) # Output: value2 print(my_dict) # Output: {'key3': 'value3'} - Deleting all elements The
.clear()method clears the dictionary, making it empty.my_dict.clear() print(my_dict) # Output: {}
Iterating through dictionary elements
1. Key iteration This is the default behavior when iterating through the dictionary.
for key in my_dict:
print(key)
2. Iterating through values Use the .values() method if you only need values.
for value in my_dict.values():
print(value)
3. Iterating through key-value pairs This is the most efficient and readable way if you need both keys and values at the same time. Use the .items() method.
for key, value in my_dict.items():
print(f"Key: {key}, Value: {value}")
main.py
Test 1
Test 2
Test 3
Test 4
Test 5
Test 6
Test 7
Test 8
Test 9
Test 10
Entwicklerlösung
