Write a function that checks whether a given string matches the format of a US phone number such as `123-456-7890`. The format requires:

- Three digits;
- A dash (`-`);
- Three more digits;
- Another dash (`-`);
- Four digits.

Use regular expressions to perform this validation. The function should return `True` if the input string matches the required pattern, and `False` otherwise.

**Example valid phone number:**

- `123-456-7890`

**Example invalid phone numbers:**

- `1234567890`  
- `123-45-6789`  
- `abc-def-ghij`



import unittest
import user_code
import ast
import re   
import unittest
import importlib

class TestTask(unittest.TestCase):
    def test_valid_number(self):
        import user_code
        importlib.reload(user_code)
        result = user_code.is_valid_phone_number("123-456-7890")
        _dynamic_test(
            self,
            result is True,
            "Returns True for valid phone number 123-456-7890",
            f"Expected True for '123-456-7890', got {result}",
        )

    def test_missing_dashes(self):
        import user_code
        importlib.reload(user_code)
        result = user_code.is_valid_phone_number("1234567890")
        _dynamic_test(
            self,
            result is False,
            "Returns False for missing dashes",
            f"Expected False for '1234567890', got {result}",
        )

    def test_wrong_digit_groups(self):
        import user_code
        importlib.reload(user_code)
        result = user_code.is_valid_phone_number("123-45-6789")
        _dynamic_test(
            self,
            result is False,
            "Returns False for incorrect digit groups",
            f"Expected False for '123-45-6789', got {result}",
        )

    def test_non_digit(self):
        import user_code
        importlib.reload(user_code)
        result = user_code.is_valid_phone_number("abc-def-ghij")
        _dynamic_test(
            self,
            result is False,
            "Returns False for non-digit input",
            f"Expected False for 'abc-def-ghij', got {result}",
        )

    def test_extra_characters(self):
        import user_code
        importlib.reload(user_code)
        result = user_code.is_valid_phone_number("123-456-7890 ")
        _dynamic_test(
            self,
            result is False,
            "Returns False for trailing space",
            f"Expected False for '123-456-7890 ', got {result}",
        )
        result2 = user_code.is_valid_phone_number(" 123-456-7890")
        _dynamic_test(
            self,
            result2 is False,
            "Returns False for leading space",
            f"Expected False for ' 123-456-7890', got {result2}",
        )
        result3 = user_code.is_valid_phone_number("123-456-7890x")
        _dynamic_test(
            self,
            result3 is False,
            "Returns False for extra character at end",
            f"Expected False for '123-456-7890x', got {result3}",
        )

    def test_partial_match(self):
        import user_code
        importlib.reload(user_code)
        result = user_code.is_valid_phone_number("0123-456-7890")
        _dynamic_test(
            self,
            result is False,
            "Returns False for too many digits at start",
            f"Expected False for '0123-456-7890', got {result}",
        )
        result2 = user_code.is_valid_phone_number("123-4567-890")
        _dynamic_test(
            self,
            result2 is False,
            "Returns False for incorrect grouping",
            f"Expected False for '123-4567-890', got {result2}",
        )

    def test_empty_string(self):
        import user_code
        importlib.reload(user_code)
        result = user_code.is_valid_phone_number("")
        _dynamic_test(
            self,
            result is False,
            "Returns False for empty string",
            f"Expected False for empty string, 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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Master advanced regex features such as lookahead/lookbehind, non-greedy matching, and apply regex to real-world text processing problems.

Challenge: Validate Phone Numbers

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Challenge: Validate Phone Numbers

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