utils.py

from itertools import chain, islice
import struct


def islice_from(it, start):
    """Given a sequence 0..start..N, iterate over start..N."""
    return islice(it, start, len(it))


def full_circle(it, start):
    """
    Given a sequence 0..start..N, iterate over start..N,
    then over 0..start.
    """
    return chain(islice_from(it, start), islice(it, start))


def log_short(s):
    """Return a string representation of s as little-endian unsigned short."""
    p = struct.pack('<H', s)
    return ''.join('{:02x}'.format(b) for b in p)


def log_int(i):
    """Return a string representation of i as little-endian unsigned int."""
    p = struct.pack('<I', i)
    return ''.join('{:02x}'.format(b) for b in p)


def log_item_fields(item):
    """Return a string representation of item's fields"""
    item_vars = sorted(vars(item).items())
    return ', '.join(k + ': ' + str(v) for k, v in item_vars
                     if not k.startswith('_'))


def first(it):
    """Return first item from collection or iterable"""
    try:
        return next(islice(it, 1))
    except StopIteration:
        return