Merge pull request #537 from realpython/python-built-in-functions

Sample code for the article on built-in functions

python-built-in-functions/README.md

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+# Python's Built-in Functions: A Complete Exploration
+
+This folder provides the code examples for the Real Python tutorial [Python's Built-in Functions: A Complete Exploration](https://realpython.com/python-built-in-functions/).

python-built-in-functions/birds.py

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+class Duck:
+    def fly(self):
+        print("The duck is flying")
+
+    def swim(self):
+        print("The duck is swimming")
+
+
+class Pigeon:
+    def fly(self):
+        print("The pigeon is flying")

python-built-in-functions/calculations.py

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+functions = [
+    "def add(a, b): return a + b",
+    "def subtract(a, b): return a - b",
+    "def multiply(a, b): return a * b",
+    "def divide(a, b): return a / b",
+]
+
+
+for function in functions:
+    exec(function)
+
+
+# Uncomment the following lines
+# print(add(1, 2))
+# print(subtract(3, 2))
+# print(multiply(2, 3))
+# print(divide(6, 3))

python-built-in-functions/circle.py

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+from time import sleep
+
+SENTINEL = object()
+
+
+class Circle:
+    def __init__(self, radius):
+        self.radius = radius
+        self._diameter = SENTINEL
+
+    @property
+    def diameter(self):
+        if self._diameter is SENTINEL:
+            sleep(0.5)  # Simulate a costly computation
+            self._diameter = self.radius * 2
+        return self._diameter
+
+
+circle = Circle(5)
+print(circle.diameter)

python-built-in-functions/commands.py

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+class CommandProcessor:
+    def __init__(self):
+        self.commands = {}
+
+    def register_command(self, command):
+        if not callable(command):
+            raise ValueError("command is not callable")
+        self.commands[command.__name__] = command
+
+    def execute_command(self, name, *args, **kwargs):
+        if (command := self.commands.get(name)) is None:
+            raise ValueError(f"command '{name}' not found")
+        return command(*args, **kwargs)
+
+
+def add(a, b):
+    return a + b
+
+
+subtract = 3 - 2
+
+
+command_processor = CommandProcessor()
+command_processor.register_command(add)
+command_processor.register_command(subtract)
+
+print(command_processor.execute_command("add", 1, 2))
+print(command_processor.register_command(subtract))

python-built-in-functions/config.json

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+{
+    "DATABASE_URL": "postgres://user:pass@localhost/dbname",
+    "DEBUG_MODE": true,
+    "MAX_CONNECTIONS": 10
+}

python-built-in-functions/config.py

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+import json
+
+
+def load_config(config_file):
+    with open(config_file) as file:
+        config = json.load(file)
+
+    globals().update(config)
+
+
+load_config("config.json")
+print(globals())

python-built-in-functions/evaluator.py

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+def evaluator(expression):
+    numbers = [2, 3, 4, 5]
+    n = len(numbers)
+    return eval(expression, {}, {"numbers": numbers, "n": n})
+
+
+print(evaluator("sum(numbers) / n + 100"))  # 3.5

python-built-in-functions/factory.py

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+def create_class(name, custom_members):
+    def __init__(self, **kwargs):
+        self.__dict__.update(kwargs)
+
+    def __repr__(self):
+        return f"{name}({self.__dict__})"
+
+    class_members = {
+        "__init__": __init__,
+        "__repr__": __repr__,
+    }
+    class_members.update(custom_members)
+
+    return type(name, (), class_members)
+
+
+User = create_class("User", {"name": "", "age": 0, "email": ""})
+Product = create_class("Product", {"name": "", "price": 0.0, "units": 0})
+
+john = User(name="John", age=30, email="[email protected]")
+table = Product(name="Table", price=200.0, units=5)

python-built-in-functions/fibonacci.py

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+class Fibonacci:
+    def __init__(self):
+        self._cache = [0, 1]
+
+    def __call__(self, index):
+        if index < len(self._cache):
+            fib_number = self._cache[index]
+            print(f"{fib_number} id = {id(fib_number)}")
+        else:
+            fib_number = self(index - 1) + self(index - 2)
+            self._cache.append(fib_number)
+        return fib_number

python-built-in-functions/files.py

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+with open("fruits.txt") as file:
+    print(file.read())

python-built-in-functions/formatting.py

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+class Formatter:
+    @staticmethod
+    def as_currency(value):
+        return f"${value:,.2f}"
+
+    @staticmethod
+    def as_percent(value):
+        return f"{value:.2%}"

python-built-in-functions/guess.py

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+from random import randint
+
+LOW, HIGH = 1, 10
+
+secret_number = randint(LOW, HIGH)
+clue = ""
+
+while True:
+    guess = input(f"Guess a number between {LOW} and {HIGH} {clue} ")
+    number = int(guess)
+    if number > secret_number:
+        clue = f"(less than {number})"
+    elif number < secret_number:
+        clue = f"(greater than {number})"
+    else:
+        break
+
+print(f"You guessed it! The secret number is {number}")

python-built-in-functions/mean.py

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+def mean(values):
+    try:
+        return sum(values) / len(values)
+    except ZeroDivisionError:
+        raise ValueError("mean() arg shouldn't be empty") from None

python-built-in-functions/menu.py

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+def list_menu(options):
+    print("Main Menu:")
+    for index, option in enumerate(options, start=1):
+        print(f"{index}. {option}")
+
+
+# Example usage
+menu_options = ["Open", "Save", "Settings", "Quit"]
+list_menu(menu_options)

python-built-in-functions/person.py

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+class Person:
+    def __init__(self, name, age):
+        self.name = name
+        self.age = age
+
+
+jane = Person("Jane", 25)
+print(getattr(jane, "name"))
+print(getattr(jane, "age"))

python-built-in-functions/point.py

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+import math
+
+
+class Point:
+    def __init__(self, x, y):
+        self.x = x
+        self.y = y
+
+    @classmethod
+    def from_polar(cls, distance, angle):
+        return cls(
+            x=distance * math.cos(math.radians(angle)),
+            y=distance * math.sin(math.radians(angle)),
+        )

python-built-in-functions/point_v1.py

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+# class Point:
+#     def __init__(self, x, y):
+#         self.x = x
+#         self.y = y
+
+
+class Point:
+    def __init__(self, x, y):
+        self.set_x(x)
+        self.set_y(y)
+
+    def get_x(self):
+        return self._x
+
+    def set_x(self, x):
+        self._x = self.validate(x)
+
+    def get_y(self):
+        return self._y
+
+    def set_y(self, y):
+        self._y = self.validate(y)
+
+    def validate(self, value):
+        if not isinstance(value, int | float):
+            raise ValueError("coordinates must be numbers")
+        return value

python-built-in-functions/point_v2.py

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+class Point:
+    def __init__(self, x, y):
+        self.x = x
+        self.y = y
+
+    @property
+    def x(self):
+        return self._x
+
+    @x.setter
+    def x(self, value):
+        self._x = self.validate(value)
+
+    @property
+    def y(self):
+        return self._y
+
+    @y.setter
+    def y(self, value):
+        self._y = self.validate(value)
+
+    def validate(self, value):
+        if not isinstance(value, int | float):
+            raise ValueError("coordinates must be numbers")
+        return value

python-built-in-functions/powers.py

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+import timeit
+
+base = 2
+exp = 1000000
+mod = 1000000
+
+print(
+    timeit.timeit("pow(base, exp) % mod", globals=globals(), number=10) * 1000
+)
+
+print(
+    timeit.timeit("pow(base, exp, mod)", globals=globals(), number=10) * 1000
+)

python-built-in-functions/processors.py

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+import csv
+import json
+
+
+class CSVProcessor:
+    def __init__(self, filename):
+        self.filename = filename
+
+    def read(self):
+        with open(self.filename, encoding="utf-8", newline="") as file:
+            return list(csv.DictReader(file))
+
+    def write(self, data):
+        with open(
+            self.filename, mode="w", encoding="utf-8", newline=""
+        ) as file:
+            writer = csv.DictWriter(file, fieldnames=data[0].keys())
+            writer.writeheader()
+            writer.writerows(data)
+
+
+class JSONProcessor:
+    def __init__(self, filename):
+        self.filename = filename
+
+    def read(self):
+        with open(self.filename, encoding="utf-8") as file:
+            return json.load(file)
+
+    def write(self, data):
+        with open(self.filename, mode="w", encoding="utf-8") as file:
+            json.dump(data, file, indent=2)
+
+
+class FileProcessor:
+    def __init__(self, filename, processor):
+        self.filename = filename
+        self.processor = processor(filename)
+
+    def __getattr__(self, attr):
+        return getattr(self.processor, attr)
+
+
+file_proc = FileProcessor("products.csv", CSVProcessor)
+print(file_proc.read())

python-built-in-functions/products.csv

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+product,price,sold_units
+Laptop,1200,30
+Phone,700,50
+Tablet,450,100
+Desktop,1000,20
+Monitor,300,50

python-built-in-functions/progress.py

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+def progress(percent=0, width=30):
+    end = ""
+    if percent == 100:
+        end = "\n"
+    left = width * percent // 100
+    right = width - left
+    print(
+        "\r[",
+        "#" * left,
+        " " * right,
+        "]",
+        f" {percent:.0f}%",
+        sep="",
+        end=end,
+        flush=True,
+    )

python-built-in-functions/reader.py

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+def read_user_input():
+    print("Enter word (type 'done' to finish):")
+    for word in iter(input, "done"):
+        print(f"Processing word: '{word}'")
+
+
+read_user_input()

python-built-in-functions/shapes.py

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+class Rectangle:
+    def __init__(self, length, width):
+        self.length = length
+        self.width = width
+
+    def area(self):
+        return self.length * self.width
+
+    def perimeter(self):
+        return 2 * (self.length + self.width)
+
+
+class Square(Rectangle):
+    def __init__(self, length):
+        super().__init__(length, length)

python-built-in-functions/stack.py

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+class Stack:
+    def __init__(self, items=None):
+        self.items = list(items) if items is not None else []
+
+    def push(self, item):
+        self.items.append(item)
+
+    def pop(self):
+        return self.items.pop()
+
+    def __bool__(self):
+        return bool(self.items)