How To Make A List Of Lists In Python When It Has Multiple Separators?

The sample file looks like this (all on one line, wrapped for legibility): ['>1\n', 'TCCGGGGGTATC\n', '>2\n', 'TCCGTGGGTATC\n', '>3\n', 'TCCGTGGGTATC\n', '>4\n', 'TC

Solution 1:

You can exploit the smaller length of the headers (and other unwanted items) as the criterion to filter them out. You start by creating a list containing one list and appending the items that pass the length test to the inner list.

A new sublist is added to the resulting list when the separator'$$$' is reached, and the length test is again used to add the remaining items to this new sublist:

lst = ['>1\n', 'TCCGGGGGTATC\n', '>2\n', 'TCCGTGGGTATC\n', '>3\n', 'TCCGTGGGTATC\n', '>4\n', 'TCCGGGGGTATC\n', '>5\n', 'TCCGTGGGTATC\n', '>6\n', 'TCCGTGGGTATC\n', '>7\n', 'TCCGTGGGTATC\n', '>8\n', 'TCCGGGGGTATC\n','\n', '$$$\n', '\n', '>B1\n', 'ATCGGGGGTATT\n', '>B2\n', 'TT-GTGGGAATC\n', '>3\n', 'TTCGTGGGAATC\n', '>B4\n', 'TT-GTGGGTATC\n', '>B5\n', 'TTCGTGGGTATT\n', '>B6\n','TTCGGGGGTATC\n', '>B7\n', 'TT-GTGGGTATC\n', '>B8\n', 'TTCGGGGGAATC\n', '>B9\n', 'TTCGGGGGTATC\n','>B10\n', 'TTCGGGGGTATC\n','>B42\n', 'TT-GTGGGTATC\n']

result = [[]]
for x in lst:
    iflen(x) > 6:
        result[-1].append(x.strip())
    if x.startswith('$$$'):
        result.append([])
print(result)
# [['TCCGGGGGTATC', 'TCCGTGGGTATC', 'TCCGTGGGTATC', 'TCCGGGGGTATC', 'TCCGTGGGTATC', 'TCCGTGGGTATC', 'TCCGTGGGTATC', 'TCCGGGGGTATC'], ['ATCGGGGGTATT', 'TT-GTGGGAATC', 'TTCGTGGGAATC', 'TT-GTGGGTATC', 'TTCGTGGGTATT', 'TTCGGGGGTATC', 'TT-GTGGGTATC', 'TTCGGGGGAATC', 'TTCGGGGGTATC', 'TTCGGGGGTATC', 'TT-GTGGGTATC']]

Solution 2:

Here is a variation of Moses Koledoye's answer which examines the first character for > and discards any matches as well as any empty elements. I also included replacing "-" with "Z".

lst = ['>1\n', 'TCCGGGGGTATC\n', '>2\n', 'TCCGTGGGTATC\n',
   '>3\n', 'TCCGTGGGTATC\n', '>4\n', 'TCCGGGGGTATC\n',
   '>5\n', 'TCCGTGGGTATC\n', '>6\n', 'TCCGTGGGTATC\n',
   '>7\n', 'TCCGTGGGTATC\n', '>8\n', 'TCCGGGGGTATC\n','\n',
   '$$$\n', '\n',
   '>B1\n', 'ATCGGGGGTATT\n', '>B2\n', 'TT-GTGGGAATC\n',
   '>3\n', 'TTCGTGGGAATC\n', '>B4\n', 'TT-GTGGGTATC\n',
   '>B5\n', 'TTCGTGGGTATT\n', '>B6\n','TTCGGGGGTATC\n',
   '>B7\n', 'TT-GTGGGTATC\n', '>B8\n', 'TTCGGGGGAATC\n',
   '>B9\n', 'TTCGGGGGTATC\n','>B10\n', 'TTCGGGGGTATC\n',
   '>B42\n', 'TT-GTGGGTATC\n']

result = [[]]for x in lst:
    if x.startswith('>'):
        continue
    if x.startswith('$$$'):
        result.append([])
        continue
    x = x.strip()
    if x:
        result[-1].append(x.replace("-", "Z"))
print(result)

This avoids assigning any particular significance to the length of any element.