Merge pull request #506 from realpython/python-built-in-exceptions

Sample code for the built-in exceptions article

Author: brendaweles

python-built-in-exceptions/README.md

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+# Python's Built-In Exceptions: A Walkthrough With Examples
+
+This folder provides the code examples for the Real Python tutorial [Python's Built-In Exceptions: A Walkthrough With Examples](https://realpython.com/python-built-in-exceptions/).

python-built-in-exceptions/average.py

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+def average_grade(grades):
+    if not grades:
+        raise ValueError("empty grades not allowed")
+    return sum(grades) / len(grades)

python-built-in-exceptions/birds.py

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+from abc import ABC
+
+
+class Bird(ABC):
+    def swim(self):
+        raise NotImplementedError("must be implemented in subclasses")
+
+    def fly(self):
+        raise NotImplementedError("must be implemented in subclasses")
+
+
+class Duck(Bird):
+    def swim(self):
+        print("The duck is swimming")
+
+    def fly(self):
+        print("The duck is flying")
+
+
+class Penguin(Bird):
+    def swim(self):
+        print("The penguin is swimming")

python-built-in-exceptions/fizzbuzz.py

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+# def fizzbuzz(number):
+#     if number % 3 == 0:
+#         return "fizz"
+#     elif number % 5 == 0:
+#         return "buzz"
+#     elif number % 15 == 0:
+#         return "fizz buzz"
+#     else:
+#         return number
+
+
+def fizzbuzz(number):
+    if number % 15 == 0:
+        return "fizz buzz"
+    elif number % 3 == 0:
+        return "fizz"
+    elif number % 5 == 0:
+        return "buzz"
+    else:
+        return number
+
+
+if __name__ == "__main__":
+    assert fizzbuzz(9) == "fizz"
+    assert fizzbuzz(10) == "buzz"
+    assert fizzbuzz(15) == "fizz buzz"
+    assert fizzbuzz(7) == 7
+    print("All tests pass")

python-built-in-exceptions/greeting.py

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+# Uncomment the following code to see the error message
+# def greet(name):
+# 	print(f"Hello, {name}!")
+#         print("Welcome to Real Python!")

python-built-in-exceptions/hello.py

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+try:
+    with open("hello.txt", mode="x") as file:
+        file.write("Hello, World!")
+except FileExistsError:
+    print("The file already exists")
+
+try:
+    with open("hello.txt", mode="r") as file:
+        print(file.read())
+except FileNotFoundError:
+    print("The file doesn't exist.")

python-built-in-exceptions/ls.py

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+import sys
+from pathlib import Path
+
+if (args_count := len(sys.argv)) > 2:
+    print(f"One argument expected, got {args_count - 1}")
+    raise SystemExit(2)
+elif args_count < 2:
+    print("You must specify the target directory")
+    raise SystemExit(2)
+
+target_dir = Path(sys.argv[1])
+
+if not target_dir.is_dir():
+    print("The target directory doesn't exist")
+    raise SystemExit(1)
+
+for entry in target_dir.iterdir():
+    print(entry.name)

python-built-in-exceptions/mean.py

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

python-built-in-exceptions/rainbow.py

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+COLORS = {
+    "Red": {"Hex": "#FF0000", "RGB": (255, 0, 0)},
+    "Orange": {"Hex": "#FF7F00", "RGB": (255, 127, 0)},
+    "Yellow": {"Hex": "#FFFF00", "RGB": (255, 255, 0)},
+    "Green": {"Hex": "#00FF00", "RGB": (0, 255, 0)},
+    "Blue": {"Hex": "#0000FF", "RGB": (0, 0, 255)},
+    "Indigo": {"Hex": "#4B0082", "RGB": (75, 0, 130)},
+    "Violet": {"Hex": "#8B00FF", "RGB": (139, 0, 255)},
+}
+
+
+class RainbowColor:
+    def __init__(self, name="Red"):
+        name = name.title()
+        if name not in COLORS:
+            raise ValueError(f"{name} is not a valid rainbow color")
+        self.name = name
+
+    def as_hex(self):
+        return COLORS[self.name]["Hex"]
+
+    def as_rgb(self):
+        return COLORS[self.name]["RGB"]

python-built-in-exceptions/square.py

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+class SquareIterator:
+    def __init__(self, values):
+        self.values = values
+        self.index = 0
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        if self.index >= len(self.values):
+            raise StopIteration
+        square = self.values[self.index] ** 2
+        self.index += 1
+        return square