Structs in Prolog

Structs in Python

Python’s classes can be used to create grouped data similar to structs in other languages. Here’s an example demonstrating the translation of structs along with some idiomatic constructs in Python.

class Person:
    def __init__(self, name, age=0):
        self.name = name
        self.age = age

def new_person(name):
    p = Person(name)
    p.age = 42
    return p

if __name__ == "__main__":
    # This syntax creates a new struct.
    print(Person("Bob", 20))

    # You can name the fields when initializing a struct.
    print(Person(name="Alice", age=30))

    # Omitted fields will be zero-valued.
    print(Person(name="Fred"))

    # An & prefix yields a pointer to the struct.
    # In Python, we typically handle this with references.
    print(vars(Person(name="Ann", age=40)))

    # It's idiomatic to encapsulate new struct creation in constructor functions.
    print(vars(new_person("Jon")))

    # Access struct fields with a dot.
    s = Person(name="Sean", age=50)
    print(s.name)

    # You can also use dots with struct pointers - the pointers are automatically dereferenced.
    sp = s
    print(sp.age)

    # Structs are mutable.
    sp.age = 51
    print(sp.age)

    # If a struct type is only used for a single value, we don’t have to give it a name.
    # The value can have an anonymous struct type. This technique is commonly used for table-driven tests.
    dog = {"name": "Rex", "isGood": True}
    print(dog)

Explanation:

Defining a Struct Equivalent:
In Python, the class keyword is used to define a new class, which can be considered an equivalent of structs.
Constructor Method (__init__):
The __init__ method initializes the data fields (name and age) in the class.
Creating Instances:
Instances of the class Person are created to hold specific people’s data, similar to how structs are created.
Anonymous Struct:
If a struct is needed only temporarily, using a dictionary {} to hold the data is a common Python idiom.

To run the program, you would place the code inside a .py file (e.g., structs.py) and then execute it with Python.

$ python structs.py
<__main__.Person object at 0x7fc0ad4e9d90>
<__main__.Person object at 0x7fc0ad4e9fd0>
<__main__.Person object at 0x7fc0ad4e9fa0>
{'name': 'Ann', 'age': 40}
{'name': 'Jon', 'age': 42}
Sean
50
51
{'name': 'Rex', 'isGood': True}

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