A Python interface to the UNIX dialog utility and mostly-compatible programs (Python 2 backport)

## WARNING

This version is a backport of pythondialog to Python 2. Unless you really have to use Python 2, you should go to the pythondialog home page and download the reference implementation which, at the time of this writing (December 2019) and for the foreseeable future, is targeted at Python 3.

This version is only here to help users who are somehow forced to still use Python 2, even though Python 3.0 was released on December 3, 2008. Python 2 has reached its end of life, and so does this backport. This backport is now unsupported. Don’t expect any further updates.

If, despite all of these warnings, you still want to use it, be sure to read the Backport-specific notes below.

## Overview

pythondialog is a Python wrapper for the UNIX dialog utility originally written by Savio Lam and later rewritten by Thomas E. Dickey. Its purpose is to provide an easy to use, pythonic and as complete as possible interface to dialog from Python code.

http://pythondialog.sourceforge.net/

and contains a short example, screenshots, a summary of the recent changes, links to the documentation, the Git repository, the mailing list, the issue tracker, etc.

If you want to get a quick idea of what this module allows one to do, you can download a release tarball and run demo.py:

PYTHONPATH=. python2 examples/demo.py

Notes:

• the preceding command uses python2 because we want to use the Python 2 backport of pythondialog;

• depending on your system, you may have to replace python2 with python or python2.7, for instance.

## What is pythondialog good for? What are its limitations?

As you might infer from the name, dialog is a high-level program that generates dialog boxes. So is pythondialog. They allow you to build nice interfaces quickly and easily, but you don’t have full control over the widgets, nor can you create new widgets without modifying dialog itself. If you need to do low-level stuff, you should have a look at ncurses (cf. the curses module in the Python standard library), blessings or slang instead. For sophisticated text-mode interfaces, the Urwid Python library looks rather interesting, too.

## Requirements

• This now unsupported backport of pythondialog requires Python 2.6 or later in the 2.x series. It has been tested with Python 2.7.

• Apart from that, pythondialog requires the dialog program (or a drop-in replacement for dialog). You can download dialog from:

https://invisible-island.net/dialog/dialog.html

Note that some features of pythondialog may require recent versions of dialog.

## Quick installation instructions

If you have a working pip setup, you should be able to install this backport of pythondialog with:

pip install python2-pythondialog

When doing so, make sure that your pip executable runs with the Python 2 installation you want to install the backport for.

For more detailed instructions, you can read the INSTALL file from a release tarball. You may also want to consult the pip documentation.

## Backport-specific notes

• The pythondialog documentation is written for the reference implementation (Python 3 at the time of this writing). To be on the safe side when using the Python 2 backport, you should use Unicode strings every time you pass “string data” to pythondialog, and you will get Unicode strings in return. Indeed, these correspond directly to Python 3 strings, and modern versions of pythondialog (>= 2.12) are all based on this type of string.

The pythondialog documentation consistently uses the term “string” (as opposed to “Unicode string”) because it has been written for Python 3, but you should definitely use Unicode strings when using the Python 2 backport. Many things happen to work with byte strings, but in most cases, this is pure coincidence; others fail, and won’t be fixed. This is not a bug.

The easiest way to use Unicode strings everywhere (or almost everywhere) in Python 2.x with x >= 6, consists in using:

from __future__ import unicode_literals

at the beginning of your Python files. This method has the additional benefit of preparing your transition to Python 3.

• Don’t use str() in Python 2 on objects such as pythondialog exceptions or dialog.DialogBackendVersion instances; use unicode() instead, which is the Python 2 equivalent of the Python 3 str() built-in. Of course, using repr() on any pythondialog object should return a byte string when run under Python 2, because this is how the repr() API works in Python 2. The same holds true for str(), but this one is not supported by the Python 2 backport of pythondialog: it is superseded, as already explained, by the much more powerful unicode().

• Before taking potentially expensive decisions, you should realize that Unicode support is much, much better in Python 3 than in Python 2, even though the basic types are largely the same (Unicode string in Python 2, native string in Python 3). In Python 3, native strings (simply called “strings” in the Python documentation) are natural and ubiquitous. They can be read and written from/to the standard I/O streams with sane encoding defaults. str() and repr() return native strings, as do all standard library calls whenever expected (i.e., when the return value is text, as opposed to binary data). Python 3 strings are both powerful and easy to use.

By contrast, in Python 2, you always have to be very careful about what you manipulate: byte strings or Unicode strings. Most library calls in your code are a potential source of bug. Usually, this kind of bug only pops up when user data or input introduces non-ASCII characters in a byte string that is then either combined with an Unicode string, or used in a context where the expected encoding is different. This means that some users get annoyed by “crappy” software, while the responsible developers are often not aware of any problem—until a bug report is filed, if ever.

Want to use traceback.format_exc() for instance? What does it return, byte string or Unicode string? Experiment. Answer: byte string. Then, how does it deal with, e.g., accented characters in an OSError exception message? Experiment. Answer: it outputs the repr() representation of an Unicode string that uses backslash escapes for the non-ASCII characters, all of this inside the returned byte string. Conclusion: the messages seen by users will be very ugly and more or less undecipherable for many of them. Does it behave this way in all cases? Tough question. Use the source, Luke…

With other library calls, you might get non-ASCII characters in a byte string. Then, the question would be: what encoding has been used to encode them, and is there a reliable way to detect it? In many cases, this is not documented and/or depends on parameters under user control, such as the locale settings. Again, you have to waste time figuring out the encoding, and often can’t be sure whether your answer is correct in all cases.

Bottom line:

There are good reasons why the Python developers broke compatibility at such a fundamental level as string management between Python 2 and Python 3. Getting Unicode support completely right in Python 2 may require more work than porting your code to Python 3. Besides, future maintainance and evolutions of your program will definitely be easier once it is written in Python 3. Think about it.

## Documentation

Important: be sure to read the Backport-specific notes above.

### The pythondialog Manual

The pythondialog Manual is written in reStructuredText format for the Sphinx documentation generator. The HTML documentation for the latest version of pythondialog as rendered by Sphinx should be available at:

http://pythondialog.sourceforge.net/doc/

The sources for the pythondialog Manual are located in the doc top-level directory of the pythondialog distribution, but the documentation build process pulls many parts from dialog.py (mainly docstrings).

Note:

Generation of the pythondialog Manual with Sphinx has only been tested, and is only supported with the reference implementation of pythondialog (i.e., currently, on Python 3). As a consequence, the package containing this file may be fine to read or grep through the .rst files; however, if compilation of said .rst files with Sphinx on Python 2 doesn’t work, it is not considered a bug—simply download the reference implementation if you want to do that.

To generate the documentation yourself from dialog.py and the sources in the doc directory, first make sure you have Sphinx and Make installed. Then, you can go to the doc directory and type, for instance:

make html

You will then find the output in the _build/html subdirectory of doc. Sphinx can build the documentation in many other formats. For instance, if you have LaTeX installed, you can generate the pythondialog Manual in PDF format using:

make latexpdf

You can run make from the doc directory to see a list of the available formats. Run make clean to clean up after the documentation build process.

For those who have installed Sphinx but not Make, it is still possible to build the documentation with a command such as:

sphinx-build -b html . _build/html

run from the doc directory. Please refer to sphinx-build for more details.

### Reading the docstrings from an interactive Python interpreter

If you have already installed pythondialog, you may consult its docstrings in an interactive Python interpreter this way:

>>> import dialog; help(dialog)

but only parts of the documentation are available using this method, and the result is much less convenient to use than the pythondialog Manual as generated by Sphinx.

## Enabling Deprecation Warnings

There are a few places in dialog.py that send a DeprecationWarning to warn developers about obsolete features. However, because of:

• the dialog output to the terminal;

• the fact that such warnings are silenced by default since Python 2.7 and 3.2;

you have to do two things in order to see them:

• redirect the standard error stream to a file;

• enable the warnings for the Python interpreter.

For instance, to see the warnings produced when running the demo, you can do:

PYTHONPATH=. python2 -Wd examples/demo.py 2>/path/to/file

and examine /path/to/file. This can also help you to find files that are still open when your program exits.

Note:

If your program is terminated by an unhandled exception while stderr is redirected as in the preceding command, you won’t see the traceback until you examine the file stderr was redirected to. This can be disturbing, as your program may exit with no apparent reason in such conditions.

For more explanations and other methods to enable deprecation warnings, please refer to:

https://docs.python.org/3/whatsnew/2.7.html

## Troubleshooting

If you have a problem with a pythondialog call, you should read its documentation and the dialog(1) manual page. If this is not enough, you can enable logging of shell command-line equivalents of all dialog calls made by your program with a simple call to Dialog.setup_debug(), first available in pythondialog 2.12 (the expand_file_opt parameter may be useful in versions 3.3 and later). An example of this can be found in demo.py from the examples directory.

As of version 2.12, you can also enable this debugging facility for demo.py by calling it with the --debug flag (possibly combined with --debug-expand-file-opt in pythondialog 3.3 and later, cf. demo.py --help).

As far as I can tell, Xdialog has not been ported to GTK+ version 2 or later. It is not in Debian stable nor unstable (November 30, 2019). It is not installed on my system (because of the GTK+ 1.2 dependency), and according to the Xdialog-specific patches I received from Peter Åstrand in 2004, was not a drop-in replacement for dialog (in particular, Xdialog seemed to want to talk to the caller through stdout instead of stderr, grrrrr!).

All this to say that, even though I didn’t remove the options to use another backend than dialog, nor did I remove the handful of little, non-invasive modifications that help pythondialog work better with Xdialog, I don’t really support the latter. I test everything with dialog, and nothing with Xdialog.

That being said, here is the old text of this section (from 2004), in case you are still interested:

Starting with 2.06, there is an “Xdialog” compatibility mode that you can use if you want pythondialog to run the graphical Xdialog program (which should be found under http://xdialog.free.fr/) instead of dialog (text-mode, based on the ncurses library).

The primary supported platform is still dialog, but as long as only small modifications are enough to make pythondialog work with Xdialog, I am willing to support Xdialog if people are interested in it (which turned out to be the case for Xdialog).

The demo.py from pythondialog 2.06 has been tested with Xdialog 2.0.6 and found to work well (barring Xdialog’s annoying behaviour with the file selection dialog box).

## Whiptail, anyone?

Well, pythondialog seems not to work very well with whiptail. The reason is that whiptail is not compatible with dialog anymore. Although you can tell pythondialog the program you want it to invoke, only programs that are mostly dialog-compatible are supported.

## History

pythondialog was originally written by Robb Shecter. Sultanbek Tezadov added some features to it (mainly the first gauge implementation, I guess). Florent Rougon rewrote most parts of the program to make it more robust and flexible so that it can give access to most features of the dialog program. Peter Åstrand took over maintainership between 2004 and 2009, with particular care for the Xdialog support. Florent Rougon took over maintainership again starting from 2009…

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