add a 1-based seqence column to a petl table

petl_sequence.py

'''
Versioned here:
https://gist.github.com/kwmiebach/362a41b0fbf0cad6db36a1e037bcfbe6
'''

def add_seq(tab,name='seq',position=0):
    # NO, PETL IS CURRENTLY BROKEN - depending on python version
    # tab = ETL.addrownumbers(tab, 'seq')

    import petl as ETL
    inner = _add_seq_gen(tab,name,position)
    return ETL.wrap(inner)

def _add_seq_gen(tab,name='seq',position=0):
    # Adds a new column with the given name
    # default name: 'seq' at the given position
    # (default: most left position).
    # The content is a 1 based sequence number.
    # You can use negative position to count from the right.

    # Make it iterable:
    itab = iter(tab)

    # Get first row (header)
    hd_list = next(itab, None)
    if hd_list is None:
        # empty table -> return an empty table
        # this is done by not yielding anything. hopefully this is ok.
        return

    # insert name at position
    hd_list = list(hd_list)
    hd_count = len(hd_list)

    # position = 0 means most left position
    # fix negative position or position > hd_count
    if position < 0:
        position = hd_count + position + 1
    if position < 0:
        position = 0
    if position > hd_count:
        position = hd_count

    hd_list.insert(position, name)
    yield tuple(hd_list)

    # all remaining rows:
    for idx, row in enumerate(itab, 1): # start enumerate from 1 as you want 1-based sequence 
        row_as_list = list(row)
        row_as_list.insert(position, idx)
        yield tuple(row_as_list)