5.11.1 shlex Objects
Keywords: lib

##
5.11.1 shlex Objects

A `shlex` instance has the following methods:

`get_token` ()
  Return a token. If tokens have been stacked using `push_token()`, pop a token off the stack. Otherwise, read one from the input stream. If reading encounters an immediate end-of-file, an empty string is returned.

`push_token` (str)
  Push the argument onto the token stack.

`read_token` ()
  Read a raw token. Ignore the pushback stack, and do not interpret source requests. (This is not ordinarily a useful entry point, and is documented here only for the sake of completeness.)

`sourcehook` (filename)
  When `shlex` detects a source request (see `source` below) this method is given the following token as argument, and expected to return a tuple consisting of a filename and an open file-like object.

  Normally, this method first strips any quotes off the argument. If the result is an absolute pathname, or there was no previous source request in effect, or the previous source was a stream (e.g. `sys.stdin`), the result is left alone. Otherwise, if the result is a relative pathname, the directory part of the name of the file immediately before it on the source inclusion stack is prepended (this behavior is like the way the C preprocessor handles `#include "file.h"`). The result of the manipulations is treated as a filename, and returned as the first component of the tuple, with `open()` called on it to yield the second component.

  This hook is exposed so that you can use it to implement directory search paths, addition of file extensions, and other namespace hacks. There is no corresponding `close' hook, but a shlex instance will call the `close()` method of the sourced input stream when it returns EOF.

`error_leader` ([file[, line]])
  This method generates an error message leader in the format of a Unix C compiler error label; the format is '"%s", line %d: ', where the "`%s`" is replaced with the name of the current source file and the "`%d`" with the current input line number (the optional arguments can be used to override these).

  This convenience is provided to encourage `shlex` users to generate error messages in the standard, parseable format understood by Emacs and other Unix tools.

Instances of `shlex` subclasses have some public instance variables which either control lexical analysis or can be used for debugging:

`commenters`
  The string of characters that are recognized as comment beginners. All characters from the comment beginner to end of line are ignored. Includes just "`#`" by default.

`wordchars`
  The string of characters that will accumulate into multi-character tokens. By default, includes all ASCII alphanumerics and underscore.

`whitespace`
  Characters that will be considered whitespace and skipped. Whitespace bounds tokens. By default, includes space, tab, linefeed and carriage-return.

`quotes`
  Characters that will be considered string quotes. The token accumulates until the same quote is encountered again (thus, different quote types protect each other as in the shell.) By default, includes ASCII single and double quotes.

`infile`
  The name of the current input file, as initially set at class instantiation time or stacked by later source requests. It may be useful to examine this when constructing error messages.

`instream`
  The input stream from which this `shlex` instance is reading characters.

`source`
  This member is `None` by default. If you assign a string to it, that string will be recognized as a lexical-level inclusion request similar to the "`source`" keyword in various shells. That is, the immediately following token will opened as a filename and input taken from that stream until EOF, at which point the `close()` method of that stream will be called and the input source will again become the original input stream. Source requests may be stacked any number of levels deep.

`debug`
  If this member is numeric and `1` or more, a `shlex` instance will print verbose progress output on its behavior. If you need to use this, you can read the module source code to learn the details.

Note that any character not declared to be a word character, whitespace, or a quote will be returned as a single-character token.

Quote and comment characters are not recognized within words. Thus, the bare words "`ain't`" and "`ain#t`" would be returned as single tokens by the default parser.

`lineno`
  Source line number (count of newlines seen so far plus one).

`token`
  The token buffer. It may be useful to examine this when catching exceptions.