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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def read_files(filenames):
 """Read a file into memory."""

    if isinstance(filenames, list):
        for filename in filenames:
            with open(filename, 'r') as infile:
                return infile.read()
    else:
        with open(filenames, 'r') as infile:
            return infile.read()