10.13.2 Using the Card Data Class

  • Create a Card`:
In [1]:
from carddataclass import Card
In [2]:
c1 = Card(Card.FACES[0], Card.SUITS[3])
  • Use Card’s autogenerated __repr__ method to display the Card
In [3]:
c1
Out[3]:
Card(face='Ace', suit='Spades')
  • Use custom __str__ method
In [4]:
print(c1)

Ace of Spades
  • Access the data class’s attributes and read-only property
In [5]:
c1.face
Out[5]:
'Ace'
In [6]:
c1.suit
Out[6]:
'Spades'
In [7]:
c1.image_name
Out[7]:
'Ace_of_Spades.png'
  • Demonstrate that Card objects can be compared via the autogenerated == operator and inherited != operator
In [8]:
c2 = Card(Card.FACES[0], Card.SUITS[3])
In [9]:
c2
Out[9]:
Card(face='Ace', suit='Spades')
In [10]:
c3 = Card(Card.FACES[0], Card.SUITS[0])
In [11]:
c3
Out[11]:
Card(face='Ace', suit='Hearts')
In [12]:
c1 == c2
Out[12]:
True
In [13]:
c1 == c3
Out[13]:
False
In [14]:
c1 != c3
Out[14]:
True
  • Card data class is interchangeable with the Card class developed earlier in this chapter
  • To demonstrate this, we created the deck2.py file containing a copy of class DeckOfCards from earlier in the chapter and imported the Card data class into the file
In [15]:
from deck2 import DeckOfCards  # uses Card data class
In [16]:
deck_of_cards = DeckOfCards()
In [17]:
print(deck_of_cards)

Ace of Hearts      2 of Hearts        3 of Hearts        4 of Hearts        
5 of Hearts        6 of Hearts        7 of Hearts        8 of Hearts        
9 of Hearts        10 of Hearts       Jack of Hearts     Queen of Hearts    
King of Hearts     Ace of Diamonds    2 of Diamonds      3 of Diamonds      
4 of Diamonds      5 of Diamonds      6 of Diamonds      7 of Diamonds      
8 of Diamonds      9 of Diamonds      10 of Diamonds     Jack of Diamonds   
Queen of Diamonds  King of Diamonds   Ace of Clubs       2 of Clubs         
3 of Clubs         4 of Clubs         5 of Clubs         6 of Clubs         
7 of Clubs         8 of Clubs         9 of Clubs         10 of Clubs        
Jack of Clubs      Queen of Clubs     King of Clubs      Ace of Spades      
2 of Spades        3 of Spades        4 of Spades        5 of Spades        
6 of Spades        7 of Spades        8 of Spades        9 of Spades        
10 of Spades       Jack of Spades     Queen of Spades    King of Spades

10.13.3 Data Class Advantages over Named Tuples

  • Objects of different named tuple types could compare as equal if they have the same number of members and the same values for those members
    • Comparing objects of different data classes always returns False, as does comparing a data class object to a tuple object
  • If you have code that unpacks a tuple, adding more members to that tuple breaks the unpacking code
    • Data class objects cannot be unpacked
    • Can add more data attributes to a data class without breaking existing code
  • A data class can be a base class or a subclass in an inheritance hierarchy

10.13.4 Data Class Advantages over Traditional Classes

  • A data class autogenerates __init__, __repr__ and __eq__, saving you time
  • A data class can autogenerate the special methods that overload the <, <=, > and >= comparison operators
  • When you change data attributes defined in a data class, the autogenerated code updates automatically
    • less code to maintain and debug
  • The required variable annotations enable you to take advantage of static code analysis tools
    • Might be able to eliminate additional errors before they can occur at execution time
    • Some static code analysis tools and IDEs can inspect variable annotations and issue warnings if your code uses the wrong type

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