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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 is_frameshift_len(mut_df):
 """Simply returns a series indicating whether each corresponding mutation is a frameshift. This is based on the length of the indel. Thus may be fooled by frameshifts at exon-intron boundaries or other odd cases. Parameters mut_df : pd.DataFrame mutation input file as a dataframe in standard format Returns ------- is_fs : pd.Series pandas series indicating if mutaitons are frameshifts """

    # calculate length, 0-based coordinates
    #indel_len = mut_df['End_Position'] - mut_df['Start_Position']
    if 'indel len' in mut_df.columns:
        indel_len = mut_df['indel len']
    else:
        indel_len = compute_indel_length(mut_df)

    # only non multiples of 3 are frameshifts
    is_fs = (indel_len%3)>0

    # make sure no single base substitutions are counted
    is_indel = (mut_df['Reference_Allele']=='-') | (mut_df['Tumor_Allele']=='-')
    is_fs[~is_indel] = False
    return is_fs