How to read lines without iterating

Question

I have a text file, and I have a condition set up where I need to extract a chunk of text every other line, but the chunk of text can be any amount of lines (a FASTA file, for any bioinformatics people). It's basically set up like this:

> header, info, info
TEXT-------------------------------------------------------
----------------------------------------------------
>header, info...
TEXT-----------------------------------------------------

... and so forth.

I am trying to extract the "TEXT" part. Here's the code I have set up:

for line in ffile:
    if line.startswith('>'):

      # do stuff to header line

        try:
            sequence = ""
            seqcheck = ffile.next() # line after the header will always be the beginning of TEXT
            while not seqcheck.startswith('>'):
                        sequence += seqcheck
                        seqcheck = ffile.next()

        except:       # iteration error check
            break

This doesn't work, because every time I call next(), it continues the for loop, which results in me skipping a lot of lines and losing a lot of data. How can I just "peek" into the next line, without moving the iterator forward?

Answer 1

I guess if you would check that data doesn't starts with '>' would be a lot easier.

>>> content = '''> header, info, info
... TEXT-------------------------------------------------------
... ----------------------------------------------------
... >header, info...
... TEXT-----------------------------------------------------'''
>>> 
>>> f = StringIO(content)
>>> 
>>> my_data = []
>>> for line in f:
...   if not line.startswith('>'):
...     my_data.append(line)
... 
>>> ''.join(my_data)
'TEXT-------------------------------------------------------\n----------------------------------------------------\nTEXT-----------------------------------------------------'
>>> 

Update:

@tobias_k this should separate lines:

>>> def get_content(f):
...   my_data = []
...   for line in f:
...     if line.startswith('>'):
...       yield my_data
...       my_data = []
...     else:
...       my_data.append(line)
...   yield my_data  # the last on
... 
>>> 
>>> f.seek(0)
>>> for i in get_content(f):
...   print i
... 
[]
['TEXT-------------------------------------------------------\n', '----------------------------------------------------\n']
['TEXT-----------------------------------------------------']
>>>