# 10.23 `distutils.text_file` -- The TextFile class

This module provides the `TextFile` class, which gives an interface to text files that (optionally) takes care of stripping comments, ignoring blank lines, and joining lines with backslashes.

class `TextFile`( | [filename=`None`, file=`None`, **options])

  This class provides a file-like object that takes care of all the things you commonly want to do when processing a text file that has some line-by-line syntax: strip comments (as long as `#` is your comment character), skip blank lines, join adjacent lines by escaping the newline (ie. backslash at end of line), strip leading and/or trailing whitespace. All of these are optional and independently controllable.

  The class provides a `warn()` method so you can generate warning messages that report physical line number, even if the logical line in question spans multiple physical lines. Also provides `unreadline()` for implementing line-at-a-time lookahead.

  `TextFile` instances are create with either filename, file, or both. `RuntimeError` is raised if both are `None`. filename should be a string, and file a file object (or something that provides `readline()` and `close()` methods). It is recommended that you supply at least filename, so that `TextFile` can include it in warning messages. If file is not supplied, `TextFile` creates its own using the `open()` built-in function.

  The options are all boolean, and affect the values returned by `readline()`

  option name | description | default
  --- | --- | ---
  strip_comments | strip from "`#`" to end-of-line, as well as any whitespace leading up to the "`#`"--unless it is escaped by a backslash | true
  lstrip_ws | strip leading whitespace from each line before returning it | false
  rstrip_ws | strip trailing whitespace (including line terminator!) from each line before returning it. | true
  skip_blanks | skip lines that are empty *after* stripping comments and whitespace. (If both lstrip_ws and rstrip_ws are false, then some lines may consist of solely whitespace: these will *not* be skipped, even if skip_blanks is true.) | true
  join_lines | if a backslash is the last non-newline character on a line after stripping comments and whitespace, join the following line to it to form one logical line; if N consecutive lines end with a backslash, then N+1 physical lines will be joined to form one logical line. | false
  collapse_join | strip leading whitespace from lines that are joined to their predecessor; only matters if "`(join_lines and not lstrip_ws)`" | false

  Note that since rstrip_ws can strip the trailing newline, the semantics of `readline()` must differ from those of the builtin file object's `readline()` method! In particular, `readline()` returns `None` for end-of-file: an empty string might just be a blank line (or an all-whitespace line), if rstrip_ws is true but skip_blanks is not.

  `open`( | filename)

    Open a new file filename. This overrides any file or filename constructor arguments.

  `close`( | )

    Close the current file and forget everything we know about it (including the filename and the current line number).

  `warn`( | msg[,line=`None`])

    Print (to stderr) a warning message tied to the current logical line in the current file. If the current logical line in the file spans multiple physical lines, the warning refers to the whole range, such as "`"lines 3-5"`". If line is supplied, it overrides the current line number; it may be a list or tuple to indicate a range of physical lines, or an integer for a single physical line.

  `readline`( | )

    Read and return a single logical line from the current file (or from an internal buffer if lines have previously been ``unread'' with `unreadline()`). If the join_lines option is true, this may involve reading multiple physical lines concatenated into a single string. Updates the current line number, so calling `warn()` after `readline()` emits a warning about the physical line(s) just read. Returns `None` on end-of-file, since the empty string can occur if rstrip_ws is true but strip_blanks is not.

  `readlines`( | )

    Read and return the list of all logical lines remaining in the current file. This updates the current line number to the last line of the file.

  `unreadline`( | line)

    Push line (a string) onto an internal buffer that will be checked by future `readline()` calls. Handy for implementing a parser with line-at-a-time lookahead. Note that lines that are ``unread'' with `unreadline` are not subsequently re-cleansed (whitespace stripped, or whatever) when read with `readline`. If multiple calls are made to `unreadline` before a call to `readline`, the lines will be returned most in most recent first order.