Added CONTRIBUTING.md

CONTRIBUTING.md

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+# Contributing guidelines
+
+## Before contributing
+
+👏👏 Welcome to [examplehub/Python](https://github.com/examplehub/Python) ! Before sending your pull requests. Please make sure that you **read the whole guidelines**.
+
+## Contributing
+
+#### How to contribute
+1. Fork the project to your github account & clone locally computer.
+2. Create an upstream remote and sync your local copy before you branch.
+3. Branch for each separate piece of work.
+4. Do the work, write good commit messages, and read the `CONTRIBUTING.md`.
+5. Push to your origin repository.
+6. Create a new PR in GitHub.
+7. Waiting to be review by the maintainers.
+
+#### Code Style
+
+#### Code Style
+* Please follow [PEP 8](https://www.python.org/dev/peps/pep-0008/) Coding Style.
+* Single letter variable names are old school so please avoid them unless their life only spans a few lines.
+* Expand acronyms because `gcd()` is hard to understand but `greatest_common_divisor()` is not.
+* Write `test unit` to test all your functions.
+* [More details](https://docs.python.org/3/tutorial/controlflow.html#intermezzo-coding-style) about Code Style.
+
+### Thanks for your contribution 😊

strings/remove_whitespace.py

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+def remove_whitespace(original: str) -> str:
+    """
+    >>> remove_whitespace("I Love Python")
+    'ILovePython'
+    >>> remove_whitespace("I    Love       Python")
+    'ILovePython'
+    >>> remove_whitespace('    I     Love     Python')
+    'ILovePython'
+    >>> remove_whitespace("")
+    ''
+    """
+    return "".join(original.split())
+
+
+def remove_whitespace2(original: str) -> str:
+    """
+    >>> remove_whitespace2("I Love Python")
+    'ILovePython'
+    >>> remove_whitespace2("I    Love       Python")
+    'ILovePython'
+    >>> remove_whitespace2('    I     Love     Python')
+    'ILovePython'
+    >>> remove_whitespace2("")
+    ''
+    """
+    return original.replace(" ", "")
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()

strings/reverse.py

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+def reverse(original: str) -> str:
+    """
+    >>> reverse("abc")
+    'cba'
+    >>> reverse('1234')
+    '4321'
+    >>> reverse("cba321")
+    '123abc'
+    >>> reverse("")
+    ''
+    """
+    return original[::-1]
+
+
+def reverse2(original: str) -> str:
+    """
+    >>> reverse2("abc")
+    'cba'
+    >>> reverse2('1234')
+    '4321'
+    >>> reverse2("cba321")
+    '123abc'
+    >>> reverse2("")
+    ''
+    """
+    original = list(original)
+    i, j = 0, len(original) - 1
+    while i < j:
+        original[i], original[j] = (
+            original[j],
+            original[i],
+        )
+        i += 1
+        j -= 1
+    return "".join(original)
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()