# Buggy code
def file(self, fmt: str, f: flow.Flow, path: mitmproxy.types.Path) -> None:
    """
    Export a flow to path.
    """
    if fmt not in formats:
        raise exceptions.CommandError("No such export format: %s" % fmt)
    func = formats[fmt]  # type: typing.Any
    v = func(f)
    with open(path, "wb") as fp:
        if isinstance(v, bytes):
            fp.write(v)
        else:
            fp.write(v.encode("utf-8"))


# 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 file(self, fmt: str, f: flow.Flow, path: mitmproxy.types.Path) -> None:
    """
    Export a flow to path.
    """
    if fmt not in formats:
        raise exceptions.CommandError("No such export format: %s" % fmt)
    func = formats[fmt]  # type: typing.Any
    v = func(f)
    try:
        with open(path, "wb") as fp:
            if isinstance(v, bytes):
                fp.write(v)
            else:
                fp.write(v.encode("utf-8"))
    except IOError as e:
        ctx.log.error(str(e))