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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 model_loader(gem_file_path, gem_file_type):
 """Consolidated function to load a GEM using COBRApy. Specify the file type being loaded. Args: gem_file_path (str):
 Path to model file gem_file_type (str):
 GEM model type - ``sbml`` (or ``xml``), ``mat``, or ``json`` format Returns: COBRApy Model object. """


    if gem_file_type.lower() == 'xml' or gem_file_type.lower() == 'sbml':
        model = read_sbml_model(gem_file_path)
    elif gem_file_type.lower() == 'mat':
        model = load_matlab_model(gem_file_path)
    elif gem_file_type.lower() == 'json':
        model = load_json_model(gem_file_path)
    else:
        raise ValueError('File type must be "sbml", "xml", "mat", or "json".')

    return model