On Wed, Oct 12, 2016 at 12:17 AM, Serhiy Storchaka firstname.lastname@example.org wrote:
On 12.10.16 09:31, Nathaniel Smith wrote:
But amortized O(1) deletes from the front of bytearray are totally different, and more like amortized O(1) appends to list: there are important use cases that simply cannot be implemented without some feature like this, and putting the implementation inside bytearray is straightforward, deterministic, and more efficiently than hacking together something on top. Python should just guarantee it, IMO.
 My use case is parsing HTTP out of a receive buffer. If deleting the first k bytes of an N byte buffer is O(N), then not only does parsing becomes O(N^2) in the worst case, but it's the sort of O(N^2) that random untrusted network clients can trigger at will to DoS your server.
Deleting from buffer can be avoided if pass the starting index together with the buffer. For example:
def read_line(buf: bytes, start: int) -> (bytes, int): try: end = buf.index(b'\r\n', start) except ValueError: return b'', start return buf[start:end], end+2
It's more complicated than that -- the right algorithm is the one that Antoine implemented in 3.4. But yes, having implemented this by hand, I am aware that it can be implemented by hand :-). My point is that forcing everyone who writes network code in Python to do that is silly, especially given that CPython's apparently been shipping this feature for years.