You will write a function that extracts all words starting with the uppercase letter **'A'** from a given string. This exercise will help you practice using basic regular expression patterns and Python's `re` module. Only words beginning with a capital 'A' should be matched—**the search must be case-sensitive**.

**Key Points:**

- Use Python's `re` module;
- Match only words that start with uppercase 'A';
- Preserve the original form of each matched word from the text.


import unittest
import user_code
import ast
import re   
import unittest
import importlib
import io
from contextlib import redirect_stdout

class TestTask(unittest.TestCase):
    def test_basic_extraction(self):
        import user_code
        importlib.reload(user_code)
        text = "Alice and Andrew went to the Aquarium."
        result = user_code.find_words_starting_with_a(text)
        expected = ["Alice", "Andrew", "Aquarium"]
        _dynamic_test(
            self,
            isinstance(result, list) and result == expected,
            f"Correctly finds words starting with 'A': {expected}",
            f"Expected {expected}, got {result}",
        )

    def test_no_matches(self):
        import user_code
        importlib.reload(user_code)
        text = "bob and charlie went home."
        result = user_code.find_words_starting_with_a(text)
        expected = []
        _dynamic_test(
            self,
            isinstance(result, list) and result == expected,
            "Returns empty list when no words start with 'A'",
            f"Expected empty list, got {result}",
        )

    def test_case_sensitive(self):
        import user_code
        importlib.reload(user_code)
        text = "apple Apple ALice aaron Aaron"
        result = user_code.find_words_starting_with_a(text)
        expected = ["Apple", "ALice", "Aaron"]
        _dynamic_test(
            self,
            isinstance(result, list) and result == expected,
            "Function is case-sensitive and includes only words starting with uppercase 'A'",
            f"Expected {expected}, got {result}",
        )

    def test_punctuation(self):
        import user_code
        importlib.reload(user_code)
        text = "Amy, Ann! Alan? Aardvark."
        result = user_code.find_words_starting_with_a(text)
        expected = ["Amy", "Ann", "Alan", "Aardvark"]
        _dynamic_test(
            self,
            isinstance(result, list) and result == expected,
            "Correctly extracts words with punctuation after them",
            f"Expected {expected}, got {result}",
        )

    def test_single_word(self):
        import user_code
        importlib.reload(user_code)
        text = "Aardvark"
        result = user_code.find_words_starting_with_a(text)
        expected = ["Aardvark"]
        _dynamic_test(
            self,
            isinstance(result, list) and result == expected,
            "Correctly returns single word starting with 'A'",
            f"Expected {expected}, got {result}",
        )

    def test_word_boundaries(self):
        import user_code
        importlib.reload(user_code)
        text = "AnA A1 A_ A!"
        result = user_code.find_words_starting_with_a(text)
        expected = ["AnA", "A1", "A_", "A"]
        _dynamic_test(
            self,
            isinstance(result, list) and result == expected,
            "Correctly matches all words starting with 'A' including numbers and underscores",
            f"Expected {expected}, got {result}",
        )

    def test_preserves_original(self):
        import user_code
        importlib.reload(user_code)
        text = "Aardvark Annabelle"
        result = user_code.find_words_starting_with_a(text)
        expected = ["Aardvark", "Annabelle"]
        _dynamic_test(
            self,
            isinstance(result, list) and result == expected,
            "Returns words exactly as they appear in the text",
            f"Expected {expected}, got {result}",
        )

def _dynamic_test(test_case, condition, success_message, failure_message):
    if condition:
        test_case._testMethodName = success_message
        test_case.assertTrue(True, success_message)
    else:
        test_case._testMethodName = failure_message
        test_case.fail(failure_message)

def normalize_text(text):
    text = text.lower()
    text = re.sub(r"\s{2,}", " ", text)
    text = re.sub(r"\s*([,:?])\s*", r"\1 ", text)
    return text.strip()

def change_var(code: str, var_name: str, value: str) -> str:
    tree = ast.parse(code)
    lines = code.splitlines()
    for i, node in enumerate(tree.body):
        if isinstance(node, ast.Assign):
            for target in node.targets:
                if isinstance(target, ast.Name) and target.id == var_name:
                    start_line = node.lineno - 1
                    line = lines[start_line]
                    indent = ' ' * (len(line) - len(line.lstrip()))
                    lines[start_line] = f"{indent}{var_name} = {value}"
                    next_line = len(lines)
                    for next_node in tree.body[i+1:]:
                        if hasattr(next_node, 'lineno'):
                            next_line = next_node.lineno - 1
                            break
                    if next_line > start_line + 1:
                        lines[start_line+1:next_line] = []
                    
                    return '\\n'.join(lines)
    return code

if __name__ == "__main__":
    unittest.main()


test_main.py

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Learn the fundamentals of regular expressions in Python, including basic syntax, pattern matching, and essential regex functions.

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Master advanced regex features such as lookahead/lookbehind, non-greedy matching, and apply regex to real-world text processing problems.

Challenge: Find Words Starting with a Specific Letter

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Challenge: Find Words Starting with a Specific Letter

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