Tip for clean tests in Python:

In most cases, your tests should cover:

- all happy path scenarios
- edge/corner/boundary cases
- negative tests
- security checks and invalid inputs

import uuid
from dataclasses import dataclass
from typing import Optional


@dataclass
class User:
    username: str


class InMemoryUserRepository:
    def __init__(self):
        self._users = []

    def add(self, user: User) -> None:
        self._users.append(user)

    def search(self, query: Optional[str] = None) -> list[User]:
        if query is None:
            return self._users
        else:
            return [
                user
                for user in self._users
                if query in user.username
            ]


# happy path
def test_search_users_without_query_lists_all_users():
    user1 = User(username="john@doe.com")
    user2 = User(username="marry@doe.com")
    repository = InMemoryUserRepository()
    repository.add(user1)
    repository.add(user2)

    assert repository.search() == [user1, user2]


# happy path
def test_search_users_with_email_part_lists_all_matching_users():
    user1 = User(username="john@doe.com")
    user2 = User(username="bob@example.com")
    user3 = User(username="marry@doe.com")
    repository = InMemoryUserRepository()
    repository.add(user1)
    repository.add(user2)
    repository.add(user3)

    assert repository.search("doe") == [user1, user3]


# edge test case
def test_search_users_with_empty_query_lists_all_users():
    user1 = User(username="john@doe.com")
    user2 = User(username="marry@doe.com")
    repository = InMemoryUserRepository()
    repository.add(user1)
    repository.add(user2)

    assert repository.search("") == [user1, user2]


# negative test case
def test_search_users_with_random_query_lists_zero_users():
    user1 = User(username="john@doe.com")
    repository = InMemoryUserRepository()
    repository.add(user1)

    assert repository.search(str(uuid.uuid4())) == []


# security test
def test_search_users_with_sql_injection_has_no_effect():
    user1 = User(username="john@doe.com")
    repository = InMemoryUserRepository()
    repository.add(user1)

    repository.search("DELETE FROM USERS;")
    assert repository.search() == [user1]

👉 @DataScience4

💀 How to encrypt a PDF with a password using Python

Ready Python script: takes a regular PDF and creates a password-protected copy.

📦 Library installation

pip install PyPDF2

⌨️ Code

from __future__ import annotations
from pathlib import Path
from typing import Union

from PyPDF2 import PdfReader, PdfWriter

PDFPath = Union[str, Path]


def encrypt_pdf(input_path: PDFPath, output_path: PDFPath, password: str) -> Path:
    """
    Encrypts a PDF file with a password and saves it to output_path.
    Returns the path to the encrypted file.
    """
    in_path = Path(input_path)
    out_path = Path(output_path)

    reader = PdfReader(in_path)
    writer = PdfWriter()

    for page in reader.pages:
        writer.add_page(page)

    writer.encrypt(password)

    with out_path.open("wb") as f:
        writer.write(f)

    return out_path


def encrypt_with_suffix(input_path: PDFPath, password: str, suffix: str = "_encrypted") -> Path:
    """
    Creates an encrypted copy next to the original file.
    For example: secret.pdf → secret_encrypted.pdf
    """
    in_path = Path(input_path)
    output_path = in_path.with_name(f"{in_path.stem}{suffix}{in_path.suffix}")
    return encrypt_pdf(in_path, output_path, password)


if __name__ == "__main__":
    pdf_file = "secret.pdf"
    pdf_password = "pythontoday"

    encrypted_path = encrypt_with_suffix(pdf_file, pdf_password)
    print(f"Encrypted file created: {encrypted_path}")

💡 Where it will be useful

🟢send a document to a client with the password via a separate channel;
🟢store important PDFs in encrypted form;
🟢integrate encryption into your service/bot/admin panel.

#python #code #tipsandtricks

https://t.me/DataScience4 🌟