# Buggy code
def save(
    self,
    flows: typing.Sequence[flow.Flow],
    cuts: mitmproxy.types.CutSpec,
    path: mitmproxy.types.Path,
) -> None:
    """
    Save cuts to file. If there are multiple flows or cuts, the format
    is UTF-8 encoded CSV. If there is exactly one row and one column,
    the data is written to file as-is, with raw bytes preserved. If the
    path is prefixed with a "+", values are appended if there is an
    existing file.
    """
    append = False
    if path.startswith("+"):
        append = True
        path = mitmproxy.types.Path(path[1:])
    if len(cuts) == 1 and len(flows) == 1:
        with open(path, "ab" if append else "wb") as fp:
            if fp.tell() > 0:
                # We're appending to a file that already exists and has content
                fp.write(b"\n")
            v = extract(cuts[0], flows[0])
            if isinstance(v, bytes):
                fp.write(v)
            else:
                fp.write(v.encode("utf8"))
        ctx.log.alert("Saved single cut.")
    else:
        with open(path, "a" if append else "w", newline="", encoding="utf8") as fp:
            writer = csv.writer(fp)
            for f in flows:
                vals = [extract(c, f) for c in cuts]
                writer.writerow(
                    [strutils.always_str(x) or "" for x in vals]  # type: ignore
                )
        ctx.log.alert("Saved %s cuts over %d flows as CSV." % (len(cuts), len(flows)))


# Traceback (PermissionError)
Traceback (most recent call last):
File "/home/kajoj/Mitmproxy/mitmproxy/mitmproxy/tools/console/master.py", line 216, in run
self.loop.run()
File "/home/kajoj/Mitmproxy/mitmproxy/venv/lib/python3.5/site-packages/urwid/main_loop.py", line 278, in run
self._run()
File "/home/kajoj/Mitmproxy/mitmproxy/venv/lib/python3.5/site-packages/urwid/main_loop.py", line 376, in _run
self.event_loop.run()
File "/home/kajoj/Mitmproxy/mitmproxy/venv/lib/python3.5/site-packages/urwid/main_loop.py", line 682, in run
self._loop()
File "/home/kajoj/Mitmproxy/mitmproxy/venv/lib/python3.5/site-packages/urwid/main_loop.py", line 719, in _loop
self._watch_files[fd]()
File "/home/kajoj/Mitmproxy/mitmproxy/venv/lib/python3.5/site-packages/urwid/raw_display.py", line 393, in <lambda>
event_loop, callback, self.get_available_raw_input())
File "/home/kajoj/Mitmproxy/mitmproxy/venv/lib/python3.5/site-packages/urwid/raw_display.py", line 493, in parse_input
callback(processed, processed_codes)
File "/home/kajoj/Mitmproxy/mitmproxy/venv/lib/python3.5/site-packages/urwid/main_loop.py", line 403, in _update
self.process_input(keys)
File "/home/kajoj/Mitmproxy/mitmproxy/venv/lib/python3.5/site-packages/urwid/main_loop.py", line 503, in process_input
k = self._topmost_widget.keypress(self.screen_size, k)
File "/home/kajoj/Mitmproxy/mitmproxy/mitmproxy/tools/console/window.py", line 318, in keypress
k = super().keypress(size, k)
File "/home/kajoj/Mitmproxy/mitmproxy/venv/lib/python3.5/site-packages/urwid/container.py", line 1116, in keypress
return self.footer.keypress((maxcol,),key)
File "/home/kajoj/Mitmproxy/mitmproxy/mitmproxy/tools/console/statusbar.py", line 149, in keypress
return self.ab.keypress(*args, **kwargs)
File "/home/kajoj/Mitmproxy/mitmproxy/mitmproxy/tools/console/statusbar.py", line 104, in keypress
self.prompt_execute(self._w.get_value())
File "/home/kajoj/Mitmproxy/mitmproxy/mitmproxy/tools/console/statusbar.py", line 124, in prompt_execute
msg = p(txt)
File "/home/kajoj/Mitmproxy/mitmproxy/mitmproxy/tools/console/commandexecutor.py", line 17, in __call__
ret = self.master.commands.call(cmd)
File "/home/kajoj/Mitmproxy/mitmproxy/mitmproxy/command.py", line 221, in call
return self.call_args(parts[0], parts[1:])
File "/home/kajoj/Mitmproxy/mitmproxy/mitmproxy/command.py", line 212, in call_args
return self.commands[path].call(args)
File "/home/kajoj/Mitmproxy/mitmproxy/mitmproxy/command.py", line 101, in call
ret = self.func(*pargs)
File "/home/kajoj/Mitmproxy/mitmproxy/mitmproxy/command.py", line 251, in wrapper
return function(*args, **kwargs)
File "/home/kajoj/Mitmproxy/mitmproxy/mitmproxy/tools/console/consoleaddons.py", line 463, in grideditor_save
with open(path, "w", newline='', encoding="utf8") as fp:
PermissionError: [Errno 13] Permission denied: '/file.txt'

# Fixed code
def save(
    self,
    flows: typing.Sequence[flow.Flow],
    cuts: mitmproxy.types.CutSpec,
    path: mitmproxy.types.Path,
) -> None:
    """
    Save cuts to file. If there are multiple flows or cuts, the format
    is UTF-8 encoded CSV. If there is exactly one row and one column,
    the data is written to file as-is, with raw bytes preserved. If the
    path is prefixed with a "+", values are appended if there is an
    existing file.
    """
    append = False
    if path.startswith("+"):
        append = True
        path = mitmproxy.types.Path(path[1:])
    try:
        if len(cuts) == 1 and len(flows) == 1:
            with open(path, "ab" if append else "wb") as fp:
                if fp.tell() > 0:
                    # We're appending to a file that already exists and has content
                    fp.write(b"\n")
                v = extract(cuts[0], flows[0])
                if isinstance(v, bytes):
                    fp.write(v)
                else:
                    fp.write(v.encode("utf8"))
            ctx.log.alert("Saved single cut.")
        else:
            with open(path, "a" if append else "w", newline="", encoding="utf8") as fp:
                writer = csv.writer(fp)
                for f in flows:
                    vals = [extract(c, f) for c in cuts]
                    writer.writerow(
                        [strutils.always_str(x) or "" for x in vals]  # type: ignore
                    )
            ctx.log.alert(
                "Saved %s cuts over %d flows as CSV." % (len(cuts), len(flows))
            )
    except IOError as e:
        ctx.log.error(str(e))