Merge pull request #566 from realpython/walrus

Add materials for Walrus tutorial

Author: KateFinegan

python-walrus-operator/README.md

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+# The Walrus Operator: Python's Assignment Expressions
+
+This folder contains the sample code used in the RealPython tutorial [The Walrus Operator: Python's Assignment Expressions](https://realpython.com/python-walrus-operator/).
+
+## About the Author
+
+Geir Arne Hjelle - Email: [email protected]
+
+## License
+
+Distributed under the MIT license. See `LICENSE` for more information.

python-walrus-operator/slow_calculations.py

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+numbers = [7, 6, 1, 4, 1, 8, 0, 6]
+
+
+def slow(number):
+    print(f"Slowly calculating {number} - 2 = {number - 2}")
+    return number - 2
+
+
+print("\nList Comprehension:")
+results = [slow(num) for num in numbers if slow(num) > 0]
+print(results)
+
+print("\nLoop")
+results = []
+for num in numbers:
+    value = slow(num)
+    if value > 0:
+        results.append(value)
+print(results)
+
+print("\nfilter()")
+results = list(filter(lambda value: value > 0, (slow(num) for num in numbers)))
+print(results)
+
+print("\nDouble List Comprehension")
+results = [value for num in numbers for value in [slow(num)] if value > 0]
+print(results)
+
+print("\nList Comprehension with Walrus Operator")
+results = [value for num in numbers if (value := slow(num)) > 0]
+print(results)

python-walrus-operator/walrus_quiz.py

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+import random
+import string
+
+QUESTIONS = {
+    "What is the formal name of PEP 572?": [
+        "Assignment Expressions",
+        "Named Expressions",
+        "The Walrus Operator",
+        "The Colon Equals Operator",
+    ],
+    "Which one of these is an invalid use of the walrus operator?": [
+        "[y**2 for x in range(10) if y := f(x) > 0]",
+        "print(y := f(x))",
+        "(y := f(x))",
+        "any((y := f(x)) for x in range(10))",
+    ],
+}
+
+num_correct = 0
+for question, answers in QUESTIONS.items():
+    correct = answers[0]
+    random.shuffle(answers)
+
+    coded_answers = dict(zip(string.ascii_lowercase, answers))
+    valid_answers = sorted(coded_answers.keys())
+
+    for code, answer in coded_answers.items():
+        print(f"  {code}) {answer}")
+
+    while (user_answer := input(f"\n{question} ")) not in valid_answers:
+        print(f"Please answer one of {', '.join(valid_answers)}")
+
+    if coded_answers[user_answer] == correct:
+        print(f"Correct, the answer is {user_answer!r}\n")
+        num_correct += 1
+    else:
+        print(f"No, the answer is {correct!r}\n")
+
+print(f"You got {num_correct} correct out of {len(QUESTIONS)} questions")

python-walrus-operator/wc.py

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+import pathlib
+import sys
+
+
+def count_words_1(filenames):
+    for filename in filenames:
+        path = pathlib.Path(filename)
+        counts = (
+            path.read_text().count("\n"),  # Number of lines
+            len(path.read_text().split()),  # Number of words
+            len(path.read_text()),  # Number of characters
+        )
+        print(*counts, path)
+
+
+def count_words_2(filenames):
+    for filename in filenames:
+        path = pathlib.Path(filename)
+        counts = (
+            (text := path.read_text()).count("\n"),  # Number of lines
+            len(text.split()),  # Number of words
+            len(text),  # Number of characters
+        )
+        print(*counts, path)
+
+
+def count_words_3(filenames):
+    for filename in filenames:
+        path = pathlib.Path(filename)
+        text = path.read_text()
+        counts = (
+            text.count("\n"),  # Number of lines
+            len(text.split()),  # Number of words
+            len(text),  # Number of characters
+        )
+        print(*counts, path)
+
+
+if __name__ == "__main__":
+    count_words_1(sys.argv[1:])
+    count_words_2(sys.argv[1:])
+    count_words_3(sys.argv[1:])