# Writing segments

Each powerline segment is a callable object. It is supposed to be either a Python function or `powerline.segments.Segment` class. As a callable object it should receive the following arguments:

Note

All received arguments are keyword arguments.

`pl`

  A `powerline.PowerlineLogger` instance. It must be used every time something needs to be logged.

`segment_info`

  A dictionary. It is only received if callable has `powerline_requires_segment_info` attribute.

  Refer to segment_info detailed description for further details.

`create_watcher`

  Function that will create filesystem watcher once called. Which watcher will be created exactly is controlled by watcher configuration option.

And also any other argument(s) specified by user in args key (no additional arguments by default).

Note

For powerline-lint to work properly the following things may be needed:

1. If segment is a `powerline.segments.Segment` instance and used arguments are scattered over multiple methods `powerline.segments.Segment.argspecobjs()` should be overridden in subclass to tell powerline-lint which objects should be inspected for arguments.

2. If segment takes some arguments that are never listed, but accessed via `kwargs.get()` or previous function cannot be used for whatever reason `powerline.segments.Segment.additional_args()` should be overridden in subclass.

3. If user is expected to use one name for multiple segments which cannot be linked to the segment function automatically by powerline-lint (e.g. because there are no instances of the segments in question in the default configuration) `powerline.lint.checks.register_common_name()` function should be used.

Object representing segment may have the following attributes used by powerline:

`powerline_requires_segment_info`

  This attribute controls whether segment will receive `segment_info` argument: if it is present argument will be received.

`powerline_requires_filesystem_watcher`

  This attribute controls whether segment will receive `create_watcher` argument: if it is present argument will be received.

`powerline_segment_datas`

  This attribute must be a dictionary containing `top_theme: segment_data` mapping where `top_theme` is any theme name (it is expected that all of the names from top-level themes list are present) and `segment_data` is a dictionary like the one that is contained inside segment_data dictionary in configuration. This attribute should be used to specify default theme-specific values for third-party segments: powerline theme-specific values go directly to top-level themes.

`startup`

  This attribute must be a callable which accepts the following keyword arguments:

  - `pl`: `powerline.PowerlineLogger` instance which is to be used for logging.

  - `shutdown_event`: `Event` object which will be set when powerline will be shut down.

  - Any arguments found in user configuration for the given segment (i.e. args key).

  This function is called at powerline startup when using long-running processes (e.g. powerline in vim, in zsh with libzpython, in ipython or in powerline daemon) and not called when `powerline-render` executable is used (more specific: when `powerline.Powerline` constructor received true `run_once` argument).

`shutdown`

  This attribute must be a callable that accepts no arguments and shuts down threads and frees any other resources allocated in `startup` method of the segment in question.

  This function is not called when `startup` method is not called.

`expand`

  This attribute must be a callable that accepts the following keyword arguments:

  - `pl`: `powerline.PowerlineLogger` instance which is to be used for logging.

  - `amount`: integer number representing amount of display cells result must occupy.

    Warning

    “Amount of display cells” is not number of Unicode codepoints, string length, or byte count. It is suggested that this function should look something like `return (' ' * amount) + segment['contents']` where `' '` may be replaced with anything that is known to occupy exactly one display cell.

  - `segment`: segment dictionary.

  - Any arguments found in user configuration for the given segment (i.e. args key).

  It must return new value of contents key.

`truncate`

  Like expand function, but for truncating segments. Here `amount` means the number of display cells which must be freed.

  This function is called for all segments before powerline starts purging them to free space.

This callable object should may return either a string (`unicode` in Python2 or `str` in Python3, not `str` in Python2 or `bytes` in Python3) object or a list of dictionaries. String object is a short form of the following return value:

    [{
        'contents': original_return,
        'highlight_groups': [segment_name],
    }]

Returned list is a list of segments treated independently, except for draw_inner_divider key.

All keys in segments returned by the function override those obtained from configuration and have the same meaning.

Detailed description of used dictionary keys:

`contents`

  Text displayed by segment. Should be a `unicode` (Python2) or `str` (Python3) instance.

`literal_contents`

  Text that needs to be output literally (i.e. without passing through `powerline.renderer.strwidth()` to determine length, through `powerline.renderer.escape()` to escape special characters and through `powerline.renderer.hl()` to highlight it). Should be a tuple `(contents_length, contents)` where `contents_length` is an integer and `contents` is a `unicode` (Python2) or `str` (Python3) instance.

  If this key is present and its second value is true then other contents keys (contents, after, before) will be ignored.

  Note

  If target is inclusion of the segment in powerline upstream all segment functions that output only subsegments with `literal_contents` key must contain the following string in documentation:

      No highlight groups are used (literal segment).

  String must be present on the separate line.

`draw_hard_divider`, `draw_soft_divider`, `draw_inner_divider`

  Determines whether given divider should be drawn. All have the same meaning as the similar keys in configuration (draw_inner_divider).

`highlight_groups`

  Determines segment highlighting. Refer to themes documentation for more details.

  Defaults to the name of the segment.

  Note

  If target is inclusion of the segment in powerline upstream all used highlighting groups must be specified in the segment documentation in the form:

      Highlight groups used: ``g1``[ or ``g2``]*[, ``g3`` (gradient)[ or ``g4``]*]*.

  I.e. use:

      Highlight groups used: ``foo_gradient`` (gradient) or ``foo``, ``bar``.

  to specify that the segment uses either `foo_gradient` group or `foo` group and `bar` group meaning that `powerline-lint` will check that at least one of the first two groups is defined (and if `foo_gradient` is defined it must use at least one gradient color) and third group is defined as well.

  All groups must be specified on one line.

`divider_highlight_group`

  Determines segment divider highlight group. Only applicable for soft dividers: colors for hard dividers are determined by colors of adjacent segments.

  Note

  If target is inclusion of the segment in powerline upstream used divider highlight group must be specified in the segment documentation in the form:

          Divider highlight group used: ``group``.

      This text must not wrap and all divider highlight group names are
      supposed to end with ``:divider``: e.g. ``cwd:divider``.

`gradient_level`

  First and the only key that may not be specified in user configuration. It determines which color should be used for this segment when one of the highlighting groups specified by highlight_groups was defined to use the color gradient.

  This key may have any value from 0 to 100 inclusive, value is supposed to be an `int` or `float` instance.

  No error occurs if segment has this key, but no used highlight groups use gradient color.

`_*`

  Keys starting with underscore are reserved for powerline and must not be returned.

`__*`

  Keys starting with two underscores are reserved for the segment functions, specifically for expand function.

## Segment dictionary

Segment dictionary contains the following keys:

- All keys returned by segment function (if it was used).

- All of the following keys:

  `name`

    Segment name: value of the name key or function name (last component of the function key). May be `None`.

  `type`

    Segment type. Always represents actual type and is never `None`.

  `highlight_groups`, `divider_highlight_group`

    Used highlight groups. May be `None`.

  `highlight_group_prefix`

    If this key is present then given prefix will be prepended to each highlight group (both regular and divider) used by this segment in a form `{prefix}:{group}` (note the colon). This key is mostly useful for segment listers.

  `before`, `after`

    Value of before or after configuration options. May be `None` as well as an empty string.

  `contents_func`

    Function used to get segment contents. May be `None`.

  `contents`

    Actual segment contents, excluding dividers and before/after. May be `None`.

  `priority`

    Segment priority. May be `None` for no priority (such segments are always shown).

  `draw_soft_divider`, `draw_hard_divider`, `draw_inner_divider`

    Divider control flags.

  `side`

    Segment side: `right` or `left`.

  `display_condition`

    Contains function that takes three position parameters: `powerline.PowerlineLogger` instance, segment_info dictionary and current mode and returns either `True` or `False` to indicate whether particular segment should be processed.

    This key is constructed based on exclude_/include_modes keys and exclude_/include_function keys.

  `width`, `align`

    Width and align options. May be `None`.

  `expand`, `truncate`

    Partially applied expand or truncate function. Accepts `pl`, `amount` and `segment` positional parameters, keyword parameters from args key were applied.

  `startup`

    Partially applied startup function. Accepts `pl` and `shutdown_event` positional parameters, keyword parameters from args key were applied.

  `shutdown`

    Shutdown function. Accepts no argument.

## Segments layout

Powerline segments are all located in one of the `powerline.segments` submodules. For extension-specific segments `powerline.segments.{ext}` module should be used (e.g. `powerline.segments.shell`), for extension-agnostic there is `powerline.segments.common`.

Plugin-specific segments (currently only those that are specific to vim plugins) should live in `powerline.segments.{ext}.plugin.{plugin_name}`: e.g. `powerline.segments.vim.plugin.gundo`.

## Segment information used in various extensions

Each `segment_info` value should be a dictionary with at least the following keys:

`environ`

  Current environment, may be an alias to `os.environ`. Is guaranteed to have `__getitem__` and `get` methods and nothing more.

  Warning

  `os.environ` must not ever be used:

  - If segment is run in the daemon this way it will get daemon’s environment which is not correct.

  - If segment is run in Vim or in zsh with libzpython `os.environ` will contain Vim or zsh environ at the moment Python interpreter was loaded.

`getcwd`

  Function that returns current working directory being called with no arguments. `os.getcwd` must not be used for the same reasons the use of `os.environ` is forbidden, except that current working directory is valid in Vim and zsh (but not in daemon).

`home`

  Current home directory. May be false.

### Vim

Vim `segment_info` argument is a dictionary with the following keys:

`window`

  `vim.Window` object. `vim.current.window` or `vim.windows[number - 1]` may be used to obtain such object. May be a false object, in which case any of this object’s properties must not be used.

`winnr`

  Window number. Same as `segment_info['window'].number` assuming Vim is new enough for `vim.Window` object to have `number` attribute.

`window_id`

  Internal powerline window id, unique for each newly created window. It is safe to assume that this ID is hashable and supports equality comparison, but no other assumptions about it should be used. Currently uses integer numbers incremented each time window is created.

`buffer`

  `vim.Buffer` object. One may be obtained using `vim.current.buffer`, `segment_info['window'].buffer` or `vim.buffers[some_number]`. Note that in the latter case depending on vim version `some_number` may be `bufnr` or the internal Vim buffer index which is not buffer number. For this reason to get `vim.Buffer` object other then stored in `segment_info` dictionary iteration over `vim.buffers` and checking their `number` attributes should be performed.

`bufnr`

  Buffer number.

`tabpage`

  `vim.Tabpage` object. One may be obtained using `vim.current.tabpage` or `vim.tabpages[number - 1]`. May be a false object, in which case no object’s properties can be used.

`tabnr`

  Tabpage number.

`mode`

  Current mode.

`encoding`

  Value of `&encoding` from the time when powerline was initialized. It should be used to convert return values.

Note

Segment generally should not assume that it is run for the current window, current buffer or current tabpage. “Current window” and “current buffer” restrictions may be ignored if `window_cached` decorator is used, “current tabpage” restriction may be safely ignored if segment is not supposed to be used in tabline.

Warning

Powerline is being tested with vim-7.0.112 (some minor sanity check) and latest Vim. This means that most of the functionality like `vim.Window.number`, `vim.*.vars`, `vim.*.options` or even `dir(vim object)` should be avoided in segments that want to be included in the upstream.

### Shell

`args`

  Parsed shell arguments: a `argparse.Namespace` object. Check out `powerline-render --help` for the list of all available arguments. Currently it is expected to contain at least the following attributes:

  `last_exit_code`

    Exit code returned by last shell command. Is either one integer, `sig{name}` or `sig{name}+core` (latter two are only seen in `rc` shell).

  `last_pipe_status`

    List of exit codes returned by last programs in the pipe or some false object. Only available in `zsh` and `rc`. Is a list of either integers, `sig{name}` or `sig{name}+core` (latter two are only seen in `rc` shell).

  `jobnum`

    Number of background jobs.

  `renderer_arg`

    Dictionary containing some keys that are additional arguments used by shell bindings. This attribute must not be used directly: all arguments from this dictionary are merged with `segment_info` dictionary. Known to have at least the following keys:

    `client_id`

      Identifier unique to one shell instance. Is used to record instance state by powerline daemon. In tmux this is the same as pane_id.

      It is not guaranteed that existing client ID will not be retaken when old shell with this ID quit: usually process PID is used as a client ID.

      It is also not guaranteed that client ID will be process PID, number or something else at all. It is guaranteed though that client ID will be some hashable object which supports equality comparison.

    `local_theme`

      Local theme that will be used by shell. One should not rely on the existence of this key.

    `pane_id`

      Identifier unique to each tmux pane. Is always an integer, optional. Obtained by using `tmux display -p '#D'`, then all leading spaces and per cent signs are stripped and the result is converted into an integer.

    Other keys, if any, are specific to segments.

### Ipython

`ipython`

  Some object which has `prompt_count` attribute. Currently it is guaranteed to have only this attribute.

  Attribute `prompt_count` contains the so-called “history count” (equivalent to `\N` in `in_template`).

### Pdb

`pdb`

  Currently active `pdb.Pdb` instance.

`curframe`

  Frame which will be run next. Note: due to the existence of `powerline.listers.pdb.frame_lister()` one must not use `segment_info['pdb'].curframe`.

`initial_stack_length`

  Equal to the length of `pdb.Pdb.stack` at the first invocation of the prompt decremented by one.

### i3wm

`mode`

  Currently active i3 mode (as a string).

`output`

  `xrandr` output name currently drawing to. Currently only available in lemonbar bindings.

`workspace`

  > the i3-ipc workspace object corresponding to this workspace. Contains string attributes `name` and `output`, as well as boolean attributes for `visible`, `urgent` and `focused`. Currently only

  provided by the `powerline.listers.i3wm.workspace_lister()` lister.

## Segment class

class `powerline.segments.``Segment`

  Base class for any segment that is not a function

  Required for powerline.lint.inspect to work properly: it defines methods for omitting existing or adding new arguments.

  Note

  Until python-3.4 `inspect.getargspec` does not support querying callable classes for arguments of their `__call__` method, requiring to use this method directly (i.e. before 3.4 you should write `getargspec(obj.__call__)` in place of `getargspec(obj)`).

  static `additional_args`()

    Returns a list of (additional argument name[, default value]) tuples.

  `argspecobjs`()

    Return a list of valid arguments for inspect.getargspec

    Used to determine function arguments.

  `omitted_args`(name, method)

    List arguments which should be omitted

    Returns a tuple with indexes of omitted arguments.

## PowerlineLogger class

class `powerline.``PowerlineLogger`(use_daemon_threads, logger, ext)

  Proxy class for logging.Logger instance

  It emits messages in format `{ext}:{prefix}:{message}` where

  `{ext}`

    is a used powerline extension (e.g. “vim”, “shell”, “ipython”).

  `{prefix}`

    is a local prefix, usually a segment name.

  `{message}`

    is the original message passed to one of the logging methods.

  Each of the methods (`critical`, `exception`, `info`, `error`, `warn`, `debug`) expects to receive message in an `str.format` format, not in printf-like format.

  Log is saved to the location specified by user.

  `critical`(msg, *args, **kwargs)
  `debug`(msg, *args, **kwargs)
  `error`(msg, *args, **kwargs)
  `exception`(msg, *args, **kwargs)
  `info`(msg, *args, **kwargs)
  `warn`(msg, *args, **kwargs)