THEORIE UND PRAXIS

Eingabe und Ausgabe

Aufgaben

Bedingungen

Aufgaben

For-Schleife

Aufgaben

Zeichenketten

Aufgaben

While-Schleife

Aufgaben

Listen

Aufgaben

2D-Arrays

Aufgaben

Wörterbücher

Aufgaben

Mengen

Aufgaben

Funktionen und Rekursion

Aufgaben

Lektion 4. Lines

Schwierigkeit:

Aufgabe«Dateinamen»

💻 Python

Du hast einen Job in einem großen Unternehmen bekommen. Deine erste Aufgabe — Hilfe bei der Automatisierung der Überprüfung von Dateien mit täglichen Berichten. Das Unternehmen hat eine strenge Regel: Alle Berichtsdateien müssen einen Namen haben, der mit dem Präfix report_ beginnt und mit der Erweiterung .txt endet. Die Namen können unterschiedlich sein, zum Beispiel: report_2025-05-06.txt oder report_sales_summary.txt.

Du musst ein Programm schreiben, das eine Liste von Dateinamen auf Einhaltung dieser Regel überprüft. Das Programm soll keine Dateien öffnen oder erstellen, es arbeitet nur mit ihren Namen in Form von Zeichenketten.

Aufgabe:
Schreibe ein Programm, das:

zuerst eine Zahl vom Benutzer einliest — die Anzahl der zu überprüfenden Dateien.
dann in einer Schleife nacheinander den Namen jeder Datei abfragt.
für jeden eingegebenen Dateinamen muss das Programm prüfen, ob er gleichzeitig zwei Bedingungen erfüllt:
- beginnt mit der Zeichenkette report_
- endet genau mit .txt
Das Programm muss sofort nach der Überprüfung der Datei auf dem Bildschirm das Ergebnis anzeigen: das Wort "correctly", wenn der Dateiname den Regeln entspricht, oder "incorrect", wenn er nicht entspricht.

Eingabeformat

Zuerst wird die Anzahl der zu überprüfenden Dateien (eine ganze Zahl) eingegeben. Dann wird in jeder neuen Zeile ein Dateiname (Zeile) eingeführt.

Ausgabeformat

Für jeden eingegebenen Dateinamen wird das Überprüfungsergebnis in der neuen Zeile angezeigt: "correct" oder "incorrect" (Zeile).

Beispiel

Eingabe

4
report_2025.txt
my_report.txt
report_data.csv
report_final_version.txt

Ausgabe

richtig
falsch
falsch
richtig

Hinweis

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(): True if all characters are numbers.
isalpha(): True if all characters are letters.
isalnum(): True if 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

Test 1

Test 2

Test 3

Test 4

Test 5

Test 6

Test 7

Test 8

Test 9

Test 10

Entwicklerlösung

# Запрашиваем у пользователя, сколько имен файлов он хочет проверить
count_str = input()
# Преобразуем полученную строку в целое число (integer)
count = int(count_str)

# Создаем цикл, который будет повторяться 'count' раз
for i in range(count):
  # На каждой итерации цикла запрашиваем имя файла
  filename = input()
  
  # Проверяем одновременно два условия с помощью 'and':
  # 1. filename.startswith("report_") - проверяет, что строка начинается с "report_"
  # 2. filename.endswith(".txt") - проверяет, что строка заканчивается на ".txt"
  if filename.startswith("report_") and filename.endswith(".txt"):
    # Если оба условия выполнены, выводим "Корректно"
    print("Корректно")
  else:
    # Если хотя бы одно из условий не выполнено, выводим "Некорректно"
    print("Некорректно")