שליטה ב-Data Classes של פייתון: סוגי שדות ועיבוד Post-Init למפתחים גלובליים

            class User:
    def __init__(self, user_id: int, username: str, email: str):
        self.user_id = user_id
        self.username = username
        self.email = email

    def __repr__(self):
        return f"User(user_id={self.user_id!r}, username={self.username!r}, email={self.email!r})"

    def __eq__(self, other):
        if not isinstance(other, User):
            return NotImplemented
        return self.user_id == other.user_id and \
               self.username == other.username and \
               self.email == other.email

            

              
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            from dataclasses import dataclass

@dataclass
class User:
    user_id: int
    username: str
    email: str

            

              
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            from dataclasses import dataclass, field

@dataclass
class Product:
    product_id: str
    name: str
    price: float
    is_available: bool = True # Default value

            

              
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            from dataclasses import dataclass, field
from typing import List

@dataclass
class Order:
    order_id: int
    items: List[str] = field(default_factory=list)
    notes: str = ""

            

              
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            from dataclasses import dataclass, field
from typing import Optional

@dataclass
class Customer:
    customer_id: int
    name: str
    contact_email: str
    internal_notes: str = field(repr=False, default="") # Not shown in repr
    loyalty_points: int = field(default=0, compare=False) # Not used in equality checks
    region: Optional[str] = field(default=None, metadata={'international_code': True})

            

              
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            from dataclasses import dataclass, field, init
import re

@dataclass
class User:
    user_id: int
    username: str
    email: str
    is_active: bool = field(default=True, init=False)

    def __post_init__(self):
        # Email validation
        if not re.match(r"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$", self.email):
            raise ValueError(f"Invalid email format: {self.email}")
        
        # Example: Setting an internal flag, not part of init
        self.is_active = True # This field was marked init=False, so we set it here

# Example of usage
try:
    user1 = User(user_id=1, username="alice", email="alice@example.com")
    print(user1)
    user2 = User(user_id=2, username="bob", email="bob@invalid-email")
except ValueError as e:
    print(e)

            

              
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            from dataclasses import dataclass, field

@dataclass
class OrderItem:
    product_name: str
    quantity: int
    unit_price: float
    total_price: float = field(init=False) # This field will be computed

    def __post_init__(self):
        if self.quantity < 0 or self.unit_price < 0:
            raise ValueError("Quantity and unit price must be non-negative.")
        self.total_price = self.quantity * self.unit_price

# Example of usage
try:
    item1 = OrderItem(product_name="Laptop", quantity=2, unit_price=1200.50)
    print(item1)
    item2 = OrderItem(product_name="Mouse", quantity=-1, unit_price=25.00)
except ValueError as e:
    print(e)

            

              
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            from dataclasses import dataclass, field
from datetime import datetime, timezone
from typing import Optional

@dataclass
class Event:
    event_name: str
    start_time_utc: datetime
    end_time_utc: datetime
    description: str = ""
    # We might store a timezone-aware datetime in UTC

    def __post_init__(self):
        # Ensure datetimes are timezone-aware (UTC in this case)
        if self.start_time_utc.tzinfo is None:
            self.start_time_utc = self.start_time_utc.replace(tzinfo=timezone.utc)
        if self.end_time_utc.tzinfo is None:
            self.end_time_utc = self.end_time_utc.replace(tzinfo=timezone.utc)

        if self.start_time_utc >= self.end_time_utc:
            raise ValueError("Start time must be before end time.")

    def get_local_time(self, tz_offset: int) -> tuple[datetime, datetime]:
        # Example: Convert UTC to a local time with a given offset (in hours)
        offset_delta = timedelta(hours=tz_offset)
        local_start = self.start_time_utc.astimezone(timezone(offset_delta))
        local_end = self.end_time_utc.astimezone(timezone(offset_delta))
        return local_start, local_end

# Example usage
now_utc = datetime.now(timezone.utc)
later_utc = now_utc + timedelta(hours=2)

try:
    conference = Event(event_name="Global Dev Summit",
                       start_time_utc=now_utc,
                       end_time_utc=later_utc)
    print(conference)

    # Get time for a European timezone (e.g., UTC+2)
    eu_start, eu_end = conference.get_local_time(2)
    print(f"European time: {eu_start.strftime('%Y-%m-%d %H:%M:%S %Z')} to {eu_end.strftime('%Y-%m-%d %H:%M:%S %Z')}")

    # Get time for a US West Coast timezone (e.g., UTC-7)
    us_west_start, us_west_end = conference.get_local_time(-7)
    print(f"US West Coast time: {us_west_start.strftime('%Y-%m-%d %H:%M:%S %Z')} to {us_west_end.strftime('%Y-%m-%d %H:%M:%S %Z')}")

except ValueError as e:
    print(e)

            

              
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            from dataclasses import dataclass, field
from decimal import Decimal
from typing import Literal

@dataclass
class MonetaryValue:
    amount: Decimal
    currency: str = field(metadata={'description': 'ISO 4217 currency code, e.g., "USD", "EUR", "JPY"'})
    # We could potentially add more fields like symbol or formatting preferences

    def __post_init__(self):
        # Basic validation for currency code length
        if not isinstance(self.currency, str) or len(self.currency) != 3 or not self.currency.isupper():
            raise ValueError(f"Invalid currency code: {self.currency}. Must be 3 uppercase letters.")
        
        # Ensure amount is a Decimal for precision
        if not isinstance(self.amount, Decimal):
            try:
                self.amount = Decimal(str(self.amount)) # Convert from float or string safely
            except Exception:
                raise TypeError(f"Amount must be convertible to Decimal. Received: {self.amount}")

    def __str__(self):
        # Basic string representation, could be enhanced with locale-specific formatting
        return f"{self.amount:.2f} {self.currency}"

# Example usage
try:
    price_usd = MonetaryValue(amount=Decimal('19.99'), currency='USD')
    print(price_usd)

    price_eur = MonetaryValue(amount=15.50, currency='EUR') # Demonstrating float to Decimal conversion
    print(price_eur)

    # Example of invalid data
    # invalid_currency = MonetaryValue(amount=100, currency='US') 
    # invalid_amount = MonetaryValue(amount='abc', currency='CAD')

except (ValueError, TypeError) as e:
    print(e)

            

              
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            from dataclasses import dataclass, field
from typing import Dict

@dataclass
class LocalizedText:
    # Use a dictionary to map language codes to text
    # Example: {'en': 'Hello', 'es': 'Hola', 'fr': 'Bonjour'}
    translations: Dict[str, str]

    def get_text(self, lang_code: str) -> str:
        return self.translations.get(lang_code, self.translations.get('en', 'No translation available'))

@dataclass
class LocalizedProduct:
    product_id: str
    name: LocalizedText
    description: LocalizedText
    price: float # Assume this is in a base currency, localization of price is complex

# Example usage
product_name_translations = {
    'en': 'Wireless Mouse',
    'es': 'Ratón Inalámbrico',
    'fr': 'Souris Sans Fil'
}

description_translations = {
    'en': 'Ergonomic wireless mouse with long battery life.',
    'es': 'Ratón inalámbrico ergonómico con batería de larga duración.',
    'fr': 'Souris sans fil ergonomique avec une longue autonomie de batterie.'
}

mouse = LocalizedProduct(
    product_id='WM-101',
    name=LocalizedText(translations=product_name_translations),
    description=LocalizedText(translations=description_translations),
    price=25.99
)

print(f"Product Name (English): {mouse.name.get_text('en')}")
print(f"Product Name (Spanish): {mouse.name.get_text('es')}")
print(f"Product Name (German): {mouse.name.get_text('de')}") # Falls back to English

print(f"Description (French): {mouse.description.get_text('fr')}")

            

              
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