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HI
🎉 ¡Felicidades! 🎉
¡Has resuelto la tarea brillantemente! Era un reto difícil, pero encontraste la solución correcta. ¡Estás un paso más cerca de dominar la programación! Sigue así, cada etapa superada te hace más fuerte.
Lección 4. Lines
Dificultad:
Tarea«Filtro de texto»
💻 Python
trabajas en el departamento de criptografía y recibiste la tarea de descifrar el mensaje interceptado. Tu colega senior descubrió que los espías utilizan un método simple pero efectivo para ocultar información útil: insertan dos caracteres aleatorios en el texto original después de cada símbolo significativo. Por lo tanto, el mensaje real está oculto en una línea larga, y para leerlo, debes tomar solo cada tercer símbolo, comenzando desde el primero (desde el índice 0).
tu tarea — Escribe un programa que automatice el proceso de descifrado. El programa debe aceptar un mensaje cifrado y mostrar el texto secreto original.
Formato de entrada
El mensaje cifrado (tipo: cadena), que debe ser procesado.
Formato de salida
Mensaje descifrado (tipo: cadena), que consiste en cada tercer símbolo de la línea original.
Ejemplo
Entrada
¡PDDRICHEVSCHECHEMTVA! A
Salida
¡Hola!
Pista
methods for working with strings in python
Python provides many built-in methods for working with strings. These are powerful tools that make it easy to manipulate text data. All methods are called with a dot after the variable in which the string is stored, according to the variable scheme.method().
It is important to remember that strings in Python are immutable. This means that none of the methods changes the original string. Instead, they return a new string with the changes applied.
Basic methods for working with strings
1. upper() and lower()
Convert all characters of the string to upper or lower case, respectively.
string = "Hello, World!"
print(string.upper()) # Output: HELLO, WORLD!
print(string.lower()) # Output: hello, world!
print(string) # Output: Hello, World! (the original line has not changed)
A useful tip: These methods are indispensable when you need to compare case-insensitive strings. For example, when checking user input.
user_input = "Yes"
if user_input.lower() =="yes":
print("The user agrees.")
2. strip(), lstrip() and rstrip()
Remove whitespace characters (spaces, tabs, line breaks) from the beginning and end of the line. lstrip() deletes only on the left, and rstrip() deletes only on the right.
string = " Hello, World! "
print(string.strip()) # Output: Hello, World!
print(string.lstrip()) # Output: Hello, World!
print(string.rstrip()) # Output: Hello, World!
A useful tip: These are extremely important methods for "cleaning" data obtained from files or from users, who often accidentally leave unnecessary spaces. As an argument, you can pass a string of characters that need to be deleted.
dirty_string = "!!!Hello, World!?! "
print(dirty_string.strip(" !?")) # Output: Hello, World
3. split() and join()
split() splits a string into a list of substrings using the specified separator. join() collects a string from the list items by inserting a separator string between them.
string = "Hello, World!"
words =string.split(", ")
print(words) # Output: ['Hello', 'World!']
# Reverse operation
joined_string = " | ".join(words)
print(joined_string) # Output: Hello | World!
A useful tip: split() is a standard method for parsing (parsing) data presented as a string, for example, CSV files. join() is the most efficient ("pythonic") way to assemble one large string from many small ones. It works much faster than adding strings in a loop using +.
4. find() and replace()
find() searches for the first occurrence of a substring and returns its index (position). If the substring is not found, returns -1. replace() replaces all occurrences of one substring with another.
string = "Hello, World!"
index = string.find("World")
print(index) # Output: 7
new_string = string.replace("World", "Python")
print(new_string) # Output: Hello, Python!
A useful tip: There is an analog of the find() index() method.. It does the same thing, but if the substring is not found, it raises the error ValueError. Use find() if the absence of a substring is a normal situation, and index(), if it should interrupt the execution of the program. The replace() method can also accept a third argument - the number of substitutions to be made.
5. startswith() and endswith()
They check whether the string begins or ends with a specific substring. Returns True or False.
string = "Hello, World!"
print(string.startswith("Hello")) # Output: True
print(string.endswith("World!")) # Output: True
print(string.startswith("Bye")) # Output: False
A useful tip: It is very convenient for quick checking of file formats (filename.endswith(".txt")) or link types (url.startswith("https")).
6. isdigit(), isalpha() and isalnum()
They check what the string consists of.
isdigit():Trueif all characters are numbers.isalpha():Trueif all characters are letters.isalnum():Trueif all characters are letters or numbers.
string1 = "12345"
string2 = "Hello"
string3 = "Hello123"
print(f"'{string1}' consists of digits? {string1.isdigit()}") # Output: True
print(f"'{string2}' consists of letters? {string2.isalpha()}") # Output: True
print(f"'{string3}' consists of letters and numbers? {string3.isalnum()}") # Output: True
print(f"'{string2}' consists of digits? {string2.isdigit()}") # Output: False
A useful tip: These methods are ideal for validating user input before attempting to convert a string to a number or using it further in the program.
A complete guide to methods
Below is a table with a more complete list of string methods for quick reference.
| Method | Purpose |
|---|---|
S.find(str, [start],[end]) |
Search for a substring in a string. Returns the number of the first occurrence or -1. |
S.rfind(str, [start],[end]) |
Search for a substring in a string. Returns the number of the last occurrence or -1. |
S.index(str, [start],[end]) |
Search for a substring in a string. Returns the number of the first occurrence or causes a ValueError. |
S.rindex(str, [start],[end]) |
Search for a substring in a string. Returns the number of the last occurrence or causes a ValueError. |
S.replace(template, replacement[, maxcount]) |
Replace the template with a replacement. maxcount limits the number of substitutions. |
S.split(character) |
Splitting a line by separator. |
S.isdigit() |
Whether the string consists of numbers. |
S.isalpha() |
Whether the string consists of letters. |
S.isalnum() |
Whether the string consists of numbers or letters. |
S.islower() |
Whether the string consists of lowercase characters. |
S.isupper() |
Whether the string consists of uppercase characters. |
S.isspace() |
Whether the string consists of non-displayed characters (space, \f, \n, \r, \t, \v). |
S.istitle() |
Whether words in a line begin with a capital letter. |
S.upper() |
Converting a string to uppercase. |
S.lower() |
Converting a string to lowercase. |
S.startswith(str) |
Does the string S start with the template str. |
S.endswith(str) |
Does line S end with the str template. |
S.join(list) |
Assembling a line from a list separated by S. |
ord(character) |
Converts a character to its ASCII/Unicode code. |
chr(number) |
Converts the ASCII/Unicode code to a character. |
S.capitalize() |
Converts the first character of the string to uppercase, and all the others to lowercase. |
S.center(width, [fill]) |
Returns a centered string with the fill character at the edges (space by default). |
S.count(str, [start],[end]) |
Returns the number of disjoint occurrences of a substring. |
S.expandtabs([tabsize]) |
Replaces the tab characters \t with spaces. |
S.lstrip([chars]) |
Deleting specified characters (or spaces) at the beginning of a line. |
S.rstrip([chars]) |
Deleting specified characters (or spaces) at the end of a line. |
S.strip([chars]) |
Deleting specified characters (or spaces) at the beginning and end of a line. |
S.partition(template) |
Divides a string by the first occurrence of the separator into three parts: before, the separator itself, and after. |
S.rpartition(sep) |
Divides the string by the last occurrence of the separator into three parts: before, the separator itself, and after. |
S.swapcase() |
Converts lowercase characters to uppercase, and uppercase characters to lowercase. |
S.title() |
Translates the first letter of each word to uppercase, and all the others to lowercase. |
S.zfill(width) |
Adds zeros to the left of the string to the length width. |
S.ljust(width, fillchar=" ") |
Aligns the line to the left, adding the characters fillchar to the right. |
S.rjust(width, fillchar=" ") |
Aligns the line to the right, adding fillchar characters to the left. |
S.format(*args, **kwargs) |
String formatting (a more modern alternative to %). |
main.py
Prueba 1
Prueba 2
Prueba 3
Prueba 4
Prueba 5
Prueba 6
Prueba 7
Prueba 8
Prueba 9
Prueba 10
Solución del desarrollador
# Получаем зашифрованное сообщение от пользователя
encrypted_message = input()
# Создаем пустую строку, в которую будем складывать расшифрованные символы
decrypted_message = encrypted_message[0]
# Используем цикл for для перебора ИНДЕКСОВ каждого символа в строке
# range(len(encrypted_message)) создаст последовательность чисел от 0 до длины строки-1
for i in range(2,len(encrypted_message),3):
decrypted_message = decrypted_message + encrypted_message[i]
# Выводим результат на экран
print(decrypted_message)
