النظرية والتطبيق

إدخال وإخراج البيانات

المهام

الشروط

المهام

حلقة for

المهام

السلاسل النصية

المهام

حلقة while

المهام

القوائم

المهام

مصفوفات ثنائية الأبعاد

المهام

القواميس

المهام

المجموعات

المهام

الدوال والتكرار

المهام

درس 8. Dictionary

الصعوبة:

مسألة«قائمة شراء أبجدية»

💻 Python

تحتاج إلى إنشاء برنامج يساعد المستخدم في إعداد قائمة مشتريات وترتيبها أبجديًا. يقوم المستخدم بإدخال اسم المنتج وكميته. يجب على البرنامج تخزين هذه المعلومات في قاموس حيث يكون اسم المنتج هو المفتاح، والكمية هي القيمة. بعد أن يكمل المستخدم إدخال المنتجات، يجب على البرنامج عرض قائمة المشتريات مرتبة أبجديًا، مع الإشارة إلى كل منتج وكميته.

تنسيق الإدخال

أولاً، يقوم المستخدم بإدخال عدد العناصر في قائمة المشتريات.
ثم لكل عنصر، يقوم المستخدم بإدخال اسم المنتج (سطر) والكمية (عدد صحيح) عبر الفجوة

تنسيق الإخراج

يجب أن يعرض البرنامج قائمة بالمشتريات مرتبة حسب الترتيب الأبجدي، حيث يحتوي كل سطر على اسم المنتج وكميته مفصولين بمسافة

مثال

إدخال

3
تفاح 5
موز 2
برتقال 3

إخراج

برتقال 3
موز 2
تفاح 5

تلميح

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.