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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 fetch_from_sdr(folder=data_folder, data='test'):
 """ Download MRS data from SDR Parameters folder : str Full path to a location in which to place the data. Per default this will be a directory under the user's home `.mrs_data`. data : str Which data to download. Either 'test', which is data required for testing, or 'example', which is data needed for the example notebooks. """

    url = "https://stacks.stanford.edu/file/druid:fn662rv4961/"

    if data == 'test':
        md5_dict = {'5182_1_1.nii.gz': '0656e59818538baa7d45311f2581bb4e',
                '5182_15_1.nii.gz': 'a5a307b581620184baf868cd0df81f89',
                'data.mat': 'a6275698f2220c65994354d412e6d82e',
                'pure_gaba_P64024.nii.gz': 'f3e09ec0f00bd9a03910b19bfe731afb'}

    elif data == 'example':
        md5_dict = {'12_1_PROBE_MEGA_L_Occ.nii.gz':
                    'a0571606c1caa16a9d9b00847771bc94',
                     '5062_2_1.nii.gz':
                    '6f77fb5134bc2841bdfc954390f0f4a4'}
        
    if not os.path.exists(folder):
        print('Creating new directory %s' % folder)
        os.makedirs(folder)
        
    for k, v in md5_dict.items():
        fname = pjoin(folder, k)
        if not os.path.exists(fname):
            print('Downloading %s from SDR ...'%k)
            _get_file_data(fname, url + k)
            check_md5(fname, v)
        else:
            print('File %s is already in place. If you want to fetch it again, please first remove it from the folder %s ' % (fname, folder))

    print('Done.')
    print('Files copied in folder %s' % folder)