THEORY AND PRACTICE

Input and Output Data

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Conditions

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For Loop

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Strings

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While Loop

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Two-Dimensional Arrays

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Dictionaries

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Sets

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Functions and Recursion

Tasks

Занятие 8. Dictionary

Difficulty level:

Task«The number of letters of the letters»

You work in a linguistic laboratory. Your colleague, a linguist, needs to analyze the text to study the frequency of occurrence of various characters. Your task & ndash; To develop a program that takes a line of text on the input and calculates how many times each symbol is found in this line. The result must be presented in the form of a “symbol: quantity” list, where each pair is displayed on a new line.

Input format

One line is supplied to the input

Output format

the program should deduce the "symbol: quantity", where the symbol & ndash; This is a symbol of the introduced line, and the quantity of & ndash; This is the number of its appearance in the line. Each couple should be bred on a new line

Example

Input

HELLO, World!

Output

h: 1
e: 1
l: 3
o: 2
,: 1
& nbsp;: 1
w: 1
r: 1
d: 1
!: 1

Hint

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 operator Deletes a key pair. Causes a KeyError error if the key is not found.
```
del my_dict["key1"]
```
Using the .pop() method Deletes 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 a KeyError, 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

Developer’s solution

🎉 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.