Returns True if the key is pressed.

        is_pressed(57) #-> True
        is_pressed('space') #-> True
        is_pressed('ctrl+space') #-> True

def is_pressed(hotkey):
    """
    Returns True if the key is pressed.

        is_pressed(57) #-> True
        is_pressed('space') #-> True
        is_pressed('ctrl+space') #-> True
    """
    _listener.start_if_necessary()

    if _is_number(hotkey):
        # Shortcut.
        with _pressed_events_lock:
            return hotkey in _pressed_events

    steps = parse_hotkey(hotkey)
    if len(steps) > 1:
        raise ValueError("Impossible to check if multi-step hotkeys are pressed (`a+b` is ok, `a, b` isn't).")

    # Convert _pressed_events into a set 
    with _pressed_events_lock:
        pressed_scan_codes = set(_pressed_events)
    for scan_codes in steps[0]:
        if not any(scan_code in pressed_scan_codes for scan_code in scan_codes):
            return False
    return True