TheAlgorithms-Python

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import re
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def dna(dna: str) -> str:
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    """
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    https://en.wikipedia.org/wiki/DNA
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    Returns the second side of a DNA strand
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    >>> dna("GCTA")
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    'CGAT'
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    >>> dna("ATGC")
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    'TACG'
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    >>> dna("CTGA")
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    'GACT'
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    >>> dna("GFGG")
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    Traceback (most recent call last):
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        ...
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    ValueError: Invalid Strand
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    """
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    if len(re.findall("[ATCG]", dna)) != len(dna):
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        raise ValueError("Invalid Strand")
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    return dna.translate(dna.maketrans("ATCG", "TAGC"))
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if __name__ == "__main__":
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    import doctest
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    doctest.testmod()
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