How to check for EOF in Python?

Question

How do I check for EOF in Python? I found a bug in my code where the last block of text after the separator isn't added to the return list. Or maybe there's a better way of expressing this function?

Here's my code:

def get_text_blocks(filename):
    text_blocks = []
    text_block = StringIO.StringIO()
    with open(filename, 'r') as f:
        for line in f:
            text_block.write(line)
            print line
            if line.startswith('-- -'):
                text_blocks.append(text_block.getvalue())
                text_block.close()
                text_block = StringIO.StringIO()
    return text_blocks

Answer 1

You might find it easier to solve this using itertools.groupby.

def get_text_blocks(filename):
    import itertools
    with open(filename,'r') as f:
        groups = itertools.groupby(f, lambda line:line.startswith('-- -'))
        return [''.join(lines) for is_separator, lines in groups if not is_separator]

Another alternative is to use a regular expression to match the separators:

def get_text_blocks(filename):
    import re
    seperator = re.compile('^-- -.*', re.M)
    with open(filename,'r') as f:
        return re.split(seperator, f.read())

Answer 2

The end-of-file condition holds as soon as the for statement terminates -- that seems the simplest way to minorly fix this code (you can extract text_block.getvalue() at the end if you want to check it's not empty before appending it).

Answer 3

This is the standard problem with emitting buffers.

You don't detect EOF -- that's needless. You write the last buffer.

def get_text_blocks(filename):
    text_blocks = []
    text_block = StringIO.StringIO()
    with open(filename, 'r') as f:
        for line in f:
            text_block.write(line)
            print line
            if line.startswith('-- -'):
                text_blocks.append(text_block.getvalue())
                text_block.close()
                text_block = StringIO.StringIO()
         ### At this moment, you are at EOF
         if len(text_block) > 0:
             text_blocks.append( text_block.getvalue() )
         ### Now your final block (if any) is appended.
    return text_blocks

Answer 4

Why do you need StringIO here?

def get_text_blocks(filename):
    text_blocks = [""]
    with open(filename, 'r') as f:
        for line in f:
            if line.startswith('-- -'):
                text_blocks.append(line)
            else: text_blocks[-1] += line          
    return text_blocks

EDIT: Fixed the function, other suggestions might be better, just wanted to write a function similar to the original one.

EDIT: Assumed the file starts with "-- -", by adding empty string to the list you can "fix" the IndexError or you could use this one:

def get_text_blocks(filename):
    text_blocks = []
    with open(filename, 'r') as f:
        for line in f:
            if line.startswith('-- -'):
                text_blocks.append(line)
            else:
                if len(text_blocks) != 0:
                    text_blocks[-1] += line          
    return text_blocks

But both versions look a bit ugly to me, the reg-ex version is much more cleaner.

Answer 5

This is a fast way to see if you have an empty file:

if f.read(1) == '': 
 print "EOF"
 f.close()