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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Lists

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Two-Dimensional Arrays

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Dictionaries

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Sets

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Functions and Recursion

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Занятие 4. Lines

Difficulty level:

Task«Text for the blog»

you & mdash; Beginning blogger. You wrote your first big article and want to make sure that you did not forget to mention the main key word for search engines (for example, "Python"). In order not to re-read the whole text with eyes, you decided to write a small assistant program.

Your program must request a full text of the article from you, and then & mdash; The key word that needs to be found. After the check, the program should give a simple answer: the word is found in the text or not.

task:
Write a program that accepts two lines to the input: the main text and tuning for the search. The program should determine whether the tuning is contained in the main text.

Input format

The main text for analysis (line)
keyword for search (line)

Output format

Search result (line)

Example

Input

Hello, peace! This is my first program.
Program

Output

The word is found

Hint

All about strings in Python: from the basics to useful tricks

A string in Python is an ordered sequence of characters. To create a string, it must be enclosed in single ('...'), double ("...") or even triple quotes ("""...""" or "'..."'), which are especially useful for multi-line texts.

The key feature of strings in Python is their immutability. This means that after creating a string, you cannot change its individual characters. Any operation that "modifies" a row actually creates a new one.

string1 = "Hello, World!"
string2 = 'Python is fun'
# Example of a multiline string
multiline_string = """This is a string
that takes
up several lines of code."""

Indexing of rows

Each character in the string has its own unique number, or index. Indexing allows us to access any single character.

It is important to remember: Indexing in Python always starts with 0, not 1. An attempt to access a non-existent index will cause an error IndexError.

w = "Python"
print(w[0]) # Output: P
print(w[1]) # Output: y
print(w[2]) #Output: t
print(w[3]) # Output: h
print(w[4]) # Output: o (not 0, as in the original example)

There is also negative indexing, which is very convenient for accessing characters from the end of a string, where -1 is the last character, -2 is the penultimate, and so on.

print(w[-1]) # Output: n (last character)
print(w[-2]) # Output: o (penultimate character)

Slicing lines

Slices are a powerful tool for extracting a part of a string (substring). They allow you to get not a single character, but a whole range.

General syntax: string[start : end : step]

start : the index from which the slice begins (this character is included in the result).
end : the index at which the slice ends (this character is not included in the result).
step : determines the interval at which characters should be extracted (the default is 1).

Examples of cross-sections

Substring extraction

string = "Hello, World!"
substring = string[0:5] # Characters 0 through 4 inclusive
print(substring) # Output: Hello

Missing starting or ending index If you omit the initial index, the slice will start from the very beginning of the row. If you omit the final one, it will continue to the very end.

string = "Hello, World!"
substring1 = string[:5] # From the beginning to index 5 (not inclusive)
substring2 = string[7:]   # From index 7 to the end of the line
print(substring1) # Output: Hello
print(substring2) # Output: World!

Using a step The step allows you to "jump over" the symbols. For example, step 2 takes every second character.

string = "Hello, World!"
substring = string[::2] # Every second character from the beginning to the end
print(substring) # Output: Hlo ol!

Negative indexes in slices They can be combined to get the parts of the string from the end.

string = "Hello, World!"
substring = string[-6:-1] # We start with the 6th character from the end and go to the 1st from the end.
print(substring) # Output: World

Useful trick: inverting the string The easiest and most popular way to flip a string is to use a slice with a step -1.

string = "Hello, World!"
reversed_string = string[::-1]
print(reversed_string) # Output: !dlroW ,olleH

Adding and multiplying strings

Addition (concatenation) is performed using the + operator. It "glues" the lines into one new one.

str1 = "Hello"
str2 = "World"
result = str1 + ", " + str2 + "!"
print(result) # Output: Hello, World!

Important advice: You cannot add a string with a number directly. To do this, the number must first be converted to a string using the str() function..

# print("Age: " + 25) # Will cause TypeError
print("Age:" + str(25)) # Correct! Output: Age: 25

Multiplication is performed using the * operator, which repeats the string a set number of times. This is useful for creating separators or formatting.

string = "Go"
result = string * 3
print(result) # Output: GoGoGo
print("-" * 20) # Output: --------------------

Useful string operations

String length The built-in len() function returns the number of characters in a string.

my_string = "Hello"
print(len(my_string))  # Will output: 5

Checking for substring occurrence The in and not in operators allow you to check whether one string is contained inside another. The result will be True or False.

Remember: this check is case-sensitive! 'd' and 'D' are different characters.

name = "Daniil"
password = "Qwerty2000!"
print('D' in name) # Outputs: True
print('d' in name) # Outputs: False
print('3' not in password) # Outputs: True

Iterating through characters in a string

The string can be iterated through in the for loop. There are two main ways, and the choice depends on the task.

Method 1: A simple search (more "pythonic") This method is used when you only need the characters of the string themselves. It's simpler and more readable.

a = "1516 the best"
for char in a: # The char variable sequentially takes the value of each character
    if char in "1234567890":
        print(char)

Method 2: Index search This method is needed when not only the symbol itself is important to you, but also its position (index).

a = "1516 the best"
for i in range(len(a)): #i will take values from 0 to len(a)-1
    if a[i] in "1234567890":
print(f"The character '{a[i]}' was found at position {i}")

Conclusion and what's next?

We have reviewed the basic but very important operations.:

Indexing to access individual characters.
Slices are an incredibly flexible tool for extracting substrings.
Concatenation (+) and repetition (*) to create new strings.

This is the foundation upon which all work with text in Python is based. To move on, study the string methods. These are built-in functions that allow you to do even more useful things with strings, for example:

.lower() / .upper() reduce the entire string to lowercase or uppercase.
.strip() - remove spaces and line breaks at the beginning and at the end.
.replace('old', 'new') replace all occurrences of one substring with another.
.split() - split a string into a list by separator (for example, by space).
.startswith('prefix') / .endswith('suffix') check whether the string begins or ends with a certain sequence of characters.

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

# Получаем основной текст от пользователя
main_text = input()

# Получаем слово, которое нужно найти
keyword = input()

# Инициализируем флаг, который покажет, найдено ли слово.
# Изначально считаем, что слово не найдено (False).
is_found = False

# Проверяем, не длиннее ли искомое слово, чем сам текст.
# Если длиннее, то его там точно нет, и цикл запускать бессмысленно.
if len(keyword) <= len(main_text):
    # Запускаем цикл, который перебирает все возможные начальные позиции для нашего слова в тексте.
    # Он идет от 0 до (длина текста - длина слова + 1).
    # +1 нужен, чтобы проверить и самый последний возможный фрагмент.
    for i in range(len(main_text) - len(keyword) + 1):
        # Внутри цикла мы "вырезаем" из основного текста фрагмент (слайс)
        # такой же длины, как и наше ключевое слово, начиная с позиции i.
        fragment = main_text[i : i + len(keyword)]
        
        # Сравниваем вырезанный фрагмент с ключевым словом.
        if fragment == keyword:
            # Если они совпали, меняем значение флага на True (слово найдено).
            is_found = True
            # И сразу же выходим из цикла, так как дальнейший поиск не имеет смысла.
            break

# После завершения цикла проверяем значение нашего флага.
if is_found:
    # Если флаг равен True, значит, слово было найдено.
    print("Слово найдено")
else:
    # Если флаг остался False, значит, цикл прошел до конца, но совпадений не было.
    print("Слово не найдено")

🎉 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.