def test_buf_del_with_negative():
lst = ['a', 'b', 'c']
buf = Buf(lst)
with buf.record() as modifications:
del buf[-1]
assert lst == ['a', 'b']
buf.apply(modifications)
assert lst == ['a', 'b', 'c']
def test_buf_set_value_idx_negative():
lst = ['a', 'b', 'c']
buf = Buf(lst)
with buf.record() as modifications:
buf[-1] = 'hello'
assert lst == ['a', 'b', 'hello']
buf.apply(modifications)
assert lst == ['a', 'b', 'c']
def ensure_loaded(
self,
status: Status,
margin: Margin,
stdin: str,
) -> None:
if self.buf:
return
if self.filename == '-':
status.update('(from stdin)')
self.filename = None
self.modified = True
sio = io.StringIO(stdin)
lines, self.nl, mixed, self.sha256 = get_lines(sio)
elif self.filename is not None and os.path.isfile(self.filename):
with open(self.filename, newline='') as f:
lines, self.nl, mixed, self.sha256 = get_lines(f)
else:
if self.filename is not None:
if os.path.lexists(self.filename):
status.update(f'{self.filename!r} is not a file')
self.filename = None
else:
status.update('(new file)')
lines, self.nl, mixed, self.sha256 = get_lines(io.StringIO(''))
self.buf = Buf(lines, self.buf.tab_size)
if mixed:
status.update(f'mixed newlines will be converted to {self.nl!r}')
self.modified = True
file_hls = []
for factory in self._hl_factories:
if self.filename is not None:
hl = factory.file_highlighter(self.filename, self.buf[0])
file_hls.append(hl)
else:
file_hls.append(factory.blank_file_highlighter())
self._file_hls = (
*file_hls,
self._trailing_whitespace,
self._replace_hl,
self.selection,
)
for file_hl in self._file_hls:
file_hl.register_callbacks(self.buf)
self.go_to_line(self.initial_line, margin)
def test_buf_iter():
buf = Buf(['a', 'b', 'c'])
buf_iter = iter(buf)
assert next(buf_iter) == 'a'
assert next(buf_iter) == 'b'
assert next(buf_iter) == 'c'
with pytest.raises(StopIteration):
next(buf_iter)
def __init__(
self,
filename: Optional[str],
initial_line: int,
color_manager: ColorManager,
hl_factories: Tuple[HLFactory, ...],
) -> None:
self.filename = filename
self.initial_line = initial_line
self.modified = False
self.buf = Buf([])
self.nl = '\n'
self.sha256: Optional[str] = None
self._in_edit_action = False
self.undo_stack: List[Action] = []
self.redo_stack: List[Action] = []
self._hl_factories = hl_factories
self._trailing_whitespace = TrailingWhitespace(color_manager)
self._replace_hl = Replace()
self.selection = Selection()
self._file_hls: Tuple[FileHL, ...] = ()
def test_buf_insert_with_negative():
lst = ['a', 'b', 'c']
buf = Buf(lst)
with buf.record() as modifications:
buf.insert(-1, 'q')
assert lst == ['a', 'b', 'q', 'c']
buf.apply(modifications)
assert lst == ['a', 'b', 'c']
def test_buf_pop_idx():
lst = ['a', 'b', 'c']
buf = Buf(lst)
with buf.record() as modifications:
buf.pop(1)
assert lst == ['a', 'c']
buf.apply(modifications)
assert lst == ['a', 'b', 'c']
def test_buf_append():
lst = ['a', 'b', 'c']
buf = Buf(lst)
with buf.record() as modifications:
buf.append('q')
assert lst == ['a', 'b', 'c', 'q']
buf.apply(modifications)
assert lst == ['a', 'b', 'c']
def _key_debug(stdscr: 'curses._CursesWindow', perf: Perf) -> int:
screen = Screen(stdscr, ['<<key debug>>'], [0], perf)
screen.file.buf = Buf([''])
while True:
screen.status.update('press q to quit')
screen.draw()
screen.file.move_cursor(screen.stdscr, screen.margin)
key = screen.get_char()
screen.file.buf.insert(-1, f'{key.wch!r} {key.keyname.decode()!r}')
screen.file.down(screen.margin)
if key.wch == curses.KEY_RESIZE:
screen.resize()
if key.wch == 'q':
return 0
def test_buf_multiple_modifications():
lst = ['a', 'b', 'c']
buf = Buf(lst)
with buf.record() as modifications:
buf[1] = 'hello'
buf.insert(1, 'ohai')
del buf[0]
assert lst == ['ohai', 'hello', 'c']
buf.apply(modifications)
assert lst == ['a', 'b', 'c']
def register_callbacks(self, buf: Buf) -> None:
buf.add_set_callback(self._set_cb)
buf.add_del_callback(self._del_cb)
buf.add_ins_callback(self._ins_cb)
class File:
def __init__(
self,
filename: Optional[str],
initial_line: int,
color_manager: ColorManager,
hl_factories: Tuple[HLFactory, ...],
) -> None:
self.filename = filename
self.initial_line = initial_line
self.modified = False
self.buf = Buf([])
self.nl = '\n'
self.sha256: Optional[str] = None
self._in_edit_action = False
self.undo_stack: List[Action] = []
self.redo_stack: List[Action] = []
self._hl_factories = hl_factories
self._trailing_whitespace = TrailingWhitespace(color_manager)
self._replace_hl = Replace()
self.selection = Selection()
self._file_hls: Tuple[FileHL, ...] = ()
def ensure_loaded(
self,
status: Status,
margin: Margin,
stdin: str,
) -> None:
if self.buf:
return
if self.filename == '-':
status.update('(from stdin)')
self.filename = None
self.modified = True
sio = io.StringIO(stdin)
lines, self.nl, mixed, self.sha256 = get_lines(sio)
elif self.filename is not None and os.path.isfile(self.filename):
with open(self.filename, newline='') as f:
lines, self.nl, mixed, self.sha256 = get_lines(f)
else:
if self.filename is not None:
if os.path.lexists(self.filename):
status.update(f'{self.filename!r} is not a file')
self.filename = None
else:
status.update('(new file)')
lines, self.nl, mixed, self.sha256 = get_lines(io.StringIO(''))
self.buf = Buf(lines, self.buf.tab_size)
if mixed:
status.update(f'mixed newlines will be converted to {self.nl!r}')
self.modified = True
file_hls = []
for factory in self._hl_factories:
if self.filename is not None:
hl = factory.file_highlighter(self.filename, self.buf[0])
file_hls.append(hl)
else:
file_hls.append(factory.blank_file_highlighter())
self._file_hls = (
*file_hls,
self._trailing_whitespace,
self._replace_hl,
self.selection,
)
for file_hl in self._file_hls:
file_hl.register_callbacks(self.buf)
self.go_to_line(self.initial_line, margin)
def __repr__(self) -> str:
return f'<{type(self).__name__} {self.filename!r}>'
# movement
@action
def up(self, margin: Margin) -> None:
self.buf.up(margin)
@action
def down(self, margin: Margin) -> None:
self.buf.down(margin)
@action
def right(self, margin: Margin) -> None:
self.buf.right(margin)
@action
def left(self, margin: Margin) -> None:
self.buf.left(margin)
@action
def home(self, margin: Margin) -> None:
self.buf.x = 0
@action
def end(self, margin: Margin) -> None:
self.buf.x = len(self.buf[self.buf.y])
@action
def ctrl_up(self, margin: Margin) -> None:
self.buf.file_up(margin)
@action
def ctrl_down(self, margin: Margin) -> None:
self.buf.file_down(margin)
@action
def ctrl_right(self, margin: Margin) -> None:
line = self.buf[self.buf.y]
# if we're at the second to last character, jump to end of line
if self.buf.x == len(line) - 1:
self.buf.right(margin)
# if we're at the end of the line, jump forward to the next non-ws
elif self.buf.x == len(line):
while (self.buf.y < len(self.buf) - 1
and (self.buf.x == len(self.buf[self.buf.y])
or self.buf[self.buf.y][self.buf.x].isspace())):
self.buf.right(margin)
# if we're inside the line, jump to next position that's not our type
else:
self.buf.right(margin)
tp = line[self.buf.x].isalnum()
while self.buf.x < len(line) and tp == line[self.buf.x].isalnum():
self.buf.right(margin)
@action
def ctrl_left(self, margin: Margin) -> None:
line = self.buf[self.buf.y]
# if we're at position 1 and it's not a space, go to the beginning
if self.buf.x == 1 and not line[:self.buf.x].isspace():
self.buf.left(margin)
# if we're at the beginning or it's all space up to here jump to the
# end of the previous non-space line
elif self.buf.x == 0 or line[:self.buf.x].isspace():
self.buf.x = 0
while self.buf.y > 0 and self.buf.x == 0:
self.buf.left(margin)
else:
self.buf.left(margin)
tp = line[self.buf.x - 1].isalnum()
while self.buf.x > 0 and tp == line[self.buf.x - 1].isalnum():
self.buf.left(margin)
@action
def ctrl_home(self, margin: Margin) -> None:
self.buf.x = 0
self.buf.y = self.buf.file_y = 0
@action
def ctrl_end(self, margin: Margin) -> None:
self.buf.x = 0
self.buf.y = len(self.buf) - 1
self.buf.scroll_screen_if_needed(margin)
@action
def go_to_line(self, lineno: int, margin: Margin) -> None:
self.buf.x = 0
if lineno == 0:
self.buf.y = 0
elif lineno > len(self.buf):
self.buf.y = len(self.buf) - 1
elif lineno < 0:
self.buf.y = max(0, lineno + len(self.buf))
else:
self.buf.y = lineno - 1
self.buf.scroll_screen_if_needed(margin)
@action
def search(
self,
reg: Pattern[str],
status: Status,
margin: Margin,
) -> None:
search = _SearchIter(self, reg, offset=1)
try:
line_y, match = next(iter(search))
except StopIteration:
status.update('no matches')
else:
if line_y == self.buf.y and match.start() == self.buf.x:
status.update('this is the only occurrence')
else:
if search.wrapped:
status.update('search wrapped')
self.buf.y = line_y
self.buf.x = match.start()
self.buf.scroll_screen_if_needed(margin)
@clear_selection
def replace(
self,
screen: 'Screen',
reg: Pattern[str],
replace: str,
) -> None:
self.finalize_previous_action()
count = 0
res: Union[str, PromptResult] = ''
search = _SearchIter(self, reg, offset=0)
for line_y, match in search:
end = match.end()
self.buf.y = line_y
self.buf.x = match.start()
self.buf.scroll_screen_if_needed(screen.margin)
if res != 'a': # make `a` replace the rest of them
with self._replace_hl.region(self.buf.y, self.buf.x, end):
screen.draw()
res = screen.quick_prompt('replace', ('yes', 'no', 'all'))
if res in {'y', 'a'}:
count += 1
with self.edit_action_context('replace', final=True):
replaced = match.expand(replace)
line = screen.file.buf[line_y]
if '\n' in replaced:
replaced_lines = replaced.split('\n')
self.buf[line_y] = (
f'{line[:match.start()]}{replaced_lines[0]}')
for i, ins_line in enumerate(replaced_lines[1:-1], 1):
self.buf.insert(line_y + i, ins_line)
last_insert = line_y + len(replaced_lines) - 1
self.buf.insert(
last_insert,
f'{replaced_lines[-1]}{line[end:]}',
)
self.buf.y = last_insert
self.buf.x = 0
search.offset = len(replaced_lines[-1])
else:
self.buf[line_y] = (
f'{line[:match.start()]}{replaced}{line[end:]}')
search.offset = len(replaced)
elif res == 'n':
search.offset = 1
else:
assert res is PromptResult.CANCELLED
return
if res == '': # we never went through the loop
screen.status.update('no matches')
else:
occurrences = 'occurrence' if count == 1 else 'occurrences'
screen.status.update(f'replaced {count} {occurrences}')
@action
def page_up(self, margin: Margin) -> None:
if self.buf.y < margin.body_lines:
self.buf.y = self.buf.file_y = 0
else:
pos = max(self.buf.file_y - margin.page_size, 0)
self.buf.y = self.buf.file_y = pos
self.buf.x = 0
@action
def page_down(self, margin: Margin) -> None:
if self.buf.file_y + margin.body_lines >= len(self.buf):
self.buf.y = len(self.buf) - 1
else:
pos = self.buf.file_y + margin.page_size
self.buf.y = self.buf.file_y = pos
self.buf.x = 0
# editing
@edit_action('backspace text', final=False)
@clear_selection
def backspace(self, margin: Margin) -> None:
# backspace at the beginning of the file does nothing
if self.buf.y == 0 and self.buf.x == 0:
pass
# backspace at the end of the file does not change the contents
elif self.buf.y == len(self.buf) - 1:
self.buf.left(margin)
# at the beginning of the line, we join the current line and
# the previous line
elif self.buf.x == 0:
y, victim = self.buf.y, self.buf.pop(self.buf.y)
self.buf.left(margin)
self.buf[y - 1] += victim
else:
s = self.buf[self.buf.y]
self.buf[self.buf.y] = s[:self.buf.x - 1] + s[self.buf.x:]
self.buf.left(margin)
@edit_action('delete text', final=False)
@clear_selection
def delete(self, margin: Margin) -> None:
if (
# noop at end of the file
self.buf.y == len(self.buf) - 1 or
# noop at end of last real line
(self.buf.y == len(self.buf) - 2
and self.buf.x == len(self.buf[self.buf.y]))):
pass
# if we're at the end of the line, collapse the line afterwards
elif self.buf.x == len(self.buf[self.buf.y]):
victim = self.buf.pop(self.buf.y + 1)
self.buf[self.buf.y] += victim
else:
s = self.buf[self.buf.y]
self.buf[self.buf.y] = s[:self.buf.x] + s[self.buf.x + 1:]
@edit_action('line break', final=False)
@clear_selection
def enter(self, margin: Margin) -> None:
s = self.buf[self.buf.y]
self.buf[self.buf.y] = s[:self.buf.x]
self.buf.insert(self.buf.y + 1, s[self.buf.x:])
self.buf.down(margin)
self.buf.x = 0
@edit_action('indent selection', final=True)
def _indent_selection(self, margin: Margin) -> None:
assert self.selection.start is not None
sel_y, sel_x = self.selection.start
(s_y, _), (e_y, _) = self.selection.get()
for l_y in range(s_y, e_y + 1):
if self.buf[l_y]:
self.buf[l_y] = ' ' * self.buf.tab_size + self.buf[l_y]
if l_y == self.buf.y:
self.buf.x += self.buf.tab_size
if l_y == sel_y and sel_x != 0:
sel_x += self.buf.tab_size
self.selection.set(sel_y, sel_x, self.buf.y, self.buf.x)
@edit_action('insert tab', final=False)
def _tab(self, margin: Margin) -> None:
n = self.buf.tab_size - self.buf.x % self.buf.tab_size
line = self.buf[self.buf.y]
self.buf[self.buf.y] = line[:self.buf.x] + n * ' ' + line[self.buf.x:]
self.buf.x += n
self.buf.restore_eof_invariant()
def tab(self, margin: Margin) -> None:
if self.selection.start is not None:
self._indent_selection(margin)
else:
self._tab(margin)
def _dedent_line(self, s: str) -> int:
bound = min(len(s), self.buf.tab_size)
i = 0
while i < bound and s[i] == ' ':
i += 1
return i
@edit_action('dedent selection', final=True)
def _dedent_selection(self, margin: Margin) -> None:
assert self.selection.start is not None
sel_y, sel_x = self.selection.start
(s_y, _), (e_y, _) = self.selection.get()
for l_y in range(s_y, e_y + 1):
n = self._dedent_line(self.buf[l_y])
if n:
self.buf[l_y] = self.buf[l_y][n:]
if l_y == self.buf.y:
self.buf.x = max(self.buf.x - n, 0)
if l_y == sel_y:
sel_x = max(sel_x - n, 0)
self.selection.set(sel_y, sel_x, self.buf.y, self.buf.x)
@edit_action('dedent', final=True)
def _dedent(self, margin: Margin) -> None:
n = self._dedent_line(self.buf[self.buf.y])
if n:
self.buf[self.buf.y] = self.buf[self.buf.y][n:]
self.buf.x = max(self.buf.x - n, 0)
def shift_tab(self, margin: Margin) -> None:
if self.selection.start is not None:
self._dedent_selection(margin)
else:
self._dedent(margin)
@edit_action('cut selection', final=True)
@clear_selection
def cut_selection(self, margin: Margin) -> Tuple[str, ...]:
ret = []
(s_y, s_x), (e_y, e_x) = self.selection.get()
if s_y == e_y:
ret.append(self.buf[s_y][s_x:e_x])
self.buf[s_y] = self.buf[s_y][:s_x] + self.buf[s_y][e_x:]
else:
ret.append(self.buf[s_y][s_x:])
for l_y in range(s_y + 1, e_y):
ret.append(self.buf[l_y])
ret.append(self.buf[e_y][:e_x])
self.buf[s_y] = self.buf[s_y][:s_x] + self.buf[e_y][e_x:]
for _ in range(s_y + 1, e_y + 1):
self.buf.pop(s_y + 1)
self.buf.y = s_y
self.buf.x = s_x
self.buf.scroll_screen_if_needed(margin)
return tuple(ret)
def cut(self, cut_buffer: Tuple[str, ...]) -> Tuple[str, ...]:
# only continue a cut if the last action is a non-final cut
if not self._continue_last_action('cut'):
cut_buffer = ()
with self.edit_action_context('cut', final=False):
if self.buf.y == len(self.buf) - 1:
return cut_buffer
else:
victim = self.buf.pop(self.buf.y)
self.buf.x = 0
return cut_buffer + (victim, )
def _uncut(self, cut_buffer: Tuple[str, ...], margin: Margin) -> None:
for cut_line in cut_buffer:
line = self.buf[self.buf.y]
before, after = line[:self.buf.x], line[self.buf.x:]
self.buf[self.buf.y] = before + cut_line
self.buf.insert(self.buf.y + 1, after)
self.buf.down(margin)
self.buf.x = 0
@edit_action('uncut', final=True)
@clear_selection
def uncut(self, cut_buffer: Tuple[str, ...], margin: Margin) -> None:
self._uncut(cut_buffer, margin)
@edit_action('uncut selection', final=True)
@clear_selection
def uncut_selection(
self,
cut_buffer: Tuple[str, ...],
margin: Margin,
) -> None:
self._uncut(cut_buffer, margin)
self.buf.up(margin)
self.buf.x = len(self.buf[self.buf.y])
self.buf[self.buf.y] += self.buf.pop(self.buf.y + 1)
self.buf.restore_eof_invariant()
def _sort(self, margin: Margin, s_y: int, e_y: int, reverse: bool) -> None:
# self.buf intentionally does not support slicing so we use islice
lines = sorted(itertools.islice(self.buf, s_y, e_y), reverse=reverse)
for i, line in zip(range(s_y, e_y), lines):
self.buf[i] = line
self.buf.y = s_y
self.buf.x = 0
self.buf.scroll_screen_if_needed(margin)
@edit_action('sort', final=True)
def sort(self, margin: Margin, reverse: bool = False) -> None:
self._sort(margin, 0, len(self.buf) - 1, reverse=reverse)
@edit_action('sort selection', final=True)
@clear_selection
def sort_selection(self, margin: Margin, reverse: bool = False) -> None:
(s_y, _), (e_y, _) = self.selection.get()
e_y = min(e_y + 1, len(self.buf) - 1)
if self.buf[e_y - 1] == '':
e_y -= 1
self._sort(margin, s_y, e_y, reverse=reverse)
DISPATCH = {
# movement
b'KEY_UP': up,
b'KEY_DOWN': down,
b'KEY_RIGHT': right,
b'KEY_LEFT': left,
b'KEY_HOME': home,
b'^A': home,
b'KEY_END': end,
b'^E': end,
b'KEY_PPAGE': page_up,
b'^Y': page_up,
b'KEY_NPAGE': page_down,
b'^V': page_down,
b'kUP5': ctrl_up,
b'kDN5': ctrl_down,
b'kRIT5': ctrl_right,
b'kLFT5': ctrl_left,
b'kHOM5': ctrl_home,
b'kEND5': ctrl_end,
# editing
b'KEY_BACKSPACE': backspace,
b'KEY_DC': delete,
b'^M': enter,
b'^I': tab,
b'KEY_BTAB': shift_tab,
# selection (shift + movement)
b'KEY_SR': keep_selection(up),
b'KEY_SF': keep_selection(down),
b'KEY_SLEFT': keep_selection(left),
b'KEY_SRIGHT': keep_selection(right),
b'KEY_SHOME': keep_selection(home),
b'KEY_SEND': keep_selection(end),
b'KEY_SPREVIOUS': keep_selection(page_up),
b'KEY_SNEXT': keep_selection(page_down),
b'kRIT6': keep_selection(ctrl_right),
b'kLFT6': keep_selection(ctrl_left),
b'kHOM6': keep_selection(ctrl_home),
b'kEND6': keep_selection(ctrl_end),
}
@edit_action('text', final=False)
@clear_selection
def c(self, wch: str, margin: Margin) -> None:
s = self.buf[self.buf.y]
self.buf[self.buf.y] = s[:self.buf.x] + wch + s[self.buf.x:]
self.buf.x += len(wch)
self.buf.restore_eof_invariant()
def finalize_previous_action(self) -> None:
assert not self._in_edit_action, 'nested edit/movement'
self.selection.clear()
if self.undo_stack:
self.undo_stack[-1].final = True
def _continue_last_action(self, name: str) -> bool:
return (bool(self.undo_stack) and self.undo_stack[-1].name == name
and not self.undo_stack[-1].final)
@contextlib.contextmanager
def edit_action_context(
self,
name: str,
*,
final: bool,
) -> Generator[None, None, None]:
continue_last = self._continue_last_action(name)
if not continue_last and self.undo_stack:
self.undo_stack[-1].final = True
before_x, before_line = self.buf.x, self.buf.y
before_modified = self.modified
assert not self._in_edit_action, f'recursive action? {name}'
self._in_edit_action = True
try:
with self.buf.record() as modifications:
yield
finally:
self._in_edit_action = False
self.redo_stack.clear()
if continue_last:
self.undo_stack[-1].end_x = self.buf.x
self.undo_stack[-1].end_y = self.buf.y
self.undo_stack[-1].modifications.extend(modifications)
elif modifications:
self.modified = True
action = Action(
name=name,
modifications=modifications,
start_x=before_x,
start_y=before_line,
start_modified=before_modified,
end_x=self.buf.x,
end_y=self.buf.y,
end_modified=True,
final=final,
)
self.undo_stack.append(action)
@contextlib.contextmanager
def select(self) -> Generator[None, None, None]:
if self.selection.start is None:
start = (self.buf.y, self.buf.x)
else:
start = self.selection.start
try:
yield
finally:
self.selection.set(*start, self.buf.y, self.buf.x)
# positioning
def move_cursor(
self,
stdscr: 'curses._CursesWindow',
margin: Margin,
) -> None:
stdscr.move(*self.buf.cursor_position(margin))
def draw(self, stdscr: 'curses._CursesWindow', margin: Margin) -> None:
to_display = min(self.buf.displayable_count, margin.body_lines)
for file_hl in self._file_hls:
# XXX: this will go away?
file_hl.highlight_until(self.buf, self.buf.file_y + to_display)
for i in range(to_display):
draw_y = i + margin.header
l_y = self.buf.file_y + i
stdscr.insstr(draw_y, 0, self.buf.rendered_line(l_y, margin))
l_x = self.buf.line_x(margin) if l_y == self.buf.y else 0
l_x_max = l_x + margin.cols
for file_hl in self._file_hls:
for region in file_hl.regions[l_y]:
l_positions = self.buf.line_positions(l_y)
r_x = l_positions[region.x]
# the selection highlight intentionally extends one past
# the end of the line, which won't have a position
if region.end == len(l_positions):
r_end = l_positions[-1] + 1
else:
r_end = l_positions[region.end]
if r_x >= l_x_max:
break
elif r_end <= l_x:
continue
if l_x and r_x <= l_x:
if file_hl.include_edge:
h_s_x = 0
else:
h_s_x = 1
else:
h_s_x = r_x - l_x
if r_end >= l_x_max and l_x_max < l_positions[-1]:
if file_hl.include_edge:
h_e_x = margin.cols
else:
h_e_x = margin.cols - 1
else:
h_e_x = r_end - l_x
stdscr.chgat(draw_y, h_s_x, h_e_x - h_s_x, region.attr)
for i in range(to_display, margin.body_lines):
stdscr.move(i + margin.header, 0)
stdscr.clrtoeol()
def test_buf_repr():
ret = repr(Buf(['a', 'b', 'c']))
assert ret == "Buf(['a', 'b', 'c'], x=0, y=0, file_y=0)"
def test_buf_item_retrieval():
buf = Buf(['a', 'b', 'c'])
assert buf[1] == 'b'
assert buf[-1] == 'c'
with pytest.raises(IndexError):
buf[3]