How to do universal newline detection on string objects in python?

While writing this question I found the answer that eluded me before.

Built-in function str.splitlines(True) allows you to determine the newline. From the docs:

For example, 'ab c\n\nde fg\rkl\r\n'.splitlines()
returns ['ab c', '', 'de fg', 'kl'],

while the same call with splitlines(True)
returns ['ab c\n', '\n', 'de fg\r', 'kl\r\n'].

Note: It is not exactly what I was looking for, since the newline is appended to chunks, so if you know a better way, please tell!

Can't you check for the presence of possible line endings in an unsplit string? e.g.

def find_line_ending(s):
    if '\r\n' in s:  # Check this one first
        return '\r\n'
    if '\r' in s:
        return '\r'
    if '\n' in s:
        return '\n'
    return None  # No line endings in string

That at least means you know what will happen in case more than one type occurs in the same string.

Here is a simple function which counts number of occurences of all three types of newline sequences in one pass throughout the string:

def countNewlines(s):
    numRN = 0;
    numR = 0;
    numN = 0;
    prev = '';
    for c in s:
        if c == '\n':
            if prev == '\r':
                numRN += 1;
            else:
                numN += 1;
        elif prev == '\r':
            numR += 1;
        prev = c;
    if prev == '\r':
        numR += 1;
    return (numRN, numR, numN);