def read_len( f ):
    """Read a 'LEN' file and return a mapping from chromosome to length"""
    mapping = dict()
    for line in f:
        fields = line.split()
        mapping[ fields[0] ] = int( fields[1] )
    return mapping
def read_len ( f ) : mapping = dict ( ) for line in f : fields = line . split ( ) mapping [ fields [ 0 ] ] = int ( fields [ 1 ] ) return mapping
Read a 'LEN' file and return a mapping from chromosome to length