Author: Patrick K. O'Brien
Date: 2003-05-08

# The wxPython wx Package

## Or, how to survive the new wx namespace changes.

Author: | Patrick K. O'Brien
Contact: | pobrien@orbtech.com
Organization: | Orbtech
Date: | 2003-05-08
Revision: | 1.1.2.4

Contents

- Introduction
- Why change anything?
- What does the new wx package do?
- Will any of this effect my existing code?
- How does the new wx package work?
- What about all the other modules, like grid, html, and stc?
- How do I use this new wx package?
- What are the issues with converting old code to use the new wx package?
- Where can I find example programs using the new wx syntax?

# Introduction

Big things sometimes come in small packages. This is certainly true of the new wx package, which is being introduced in wxPython 2.4.1 as a way to allow the "wx" prefix to be dropped from the names of all wxPython classes, functions, and constants. This document should answer all the questions you might have concerning the new wx package. If not, feel free to contact the author. I hope you like the new wx package as much as I do.

# Why change anything?

This change is being made for a couple of reasons. The first reason is to discourage the use of `import *`, which is a dangerous technique that can create name conflicts and bloated namespaces.

The second reason is to remove what some perceive to be a "wart." For example, the following code is rather ugly in that the "wx" prefix on the wxFrame class name is no longer useful when you're using the wx module prefix:

    from wxPython import wx

    class Frame(wx.wxFrame)

The new wx package allows you to write code like this, instead:

    import wx

    class Frame(wx.Frame)

The third reason is that the wxWindows project intends to do the same thing (implement a new wx namespace and drop the "wx" prefix) and we want wxPython to lead the way.

# What does the new wx package do?

As a way of getting to this new syntax as quickly as possible, the code in this new wx package was created. What it does is alter the existing wx namespace dynamically. By making the changes on-the-fly at runtime, we can try out the new syntax before any permanent changes are made to the underlying class library. The downside of making these changes at runtime is that there is a slight delay when you `import wx`; the upside is that you can start using the new syntax now.

# Will any of this effect my existing code?

No. Your existing code will continue to work and be supported for some time. It will be up to you to decide when to switch to the new syntax. But all new documentation and code examples will use the new syntax. So don't wait too long. You wouldn't want anyone calling you old-fashioned, would you?

# How does the new wx package work?

It's pretty simple, and pretty clever. The wx directory contains an `__init__.py` file, making it a Python package. (In contrast, the old wxPython.wx module is a module, not a package.) When you `import wx` the code in the `__init__.py` file is executed, and that's where all the magic takes place. Let's take a look at the code inside the `__init__.py` file:

    """wx package

    Provides a way to drop the wx prefix from wxPython objects."""

    __author__ = "Patrick K. O'Brien <pobrien@orbtech.com>"
    __cvsid__ = "$Id: wxPackage.html,v 1.1.2.1 2003/06/05 23:18:13 RD Exp $"
    __revision__ = "$Revision: 1.1.2.1 $"[11:-2]

    from wxPython import wx

    import types

    d_new = globals()
    d_old = wx.__dict__

    for old, obj in d_old.items():
        if type(obj) is types.ModuleType or old.startswith('_'):
            # Skip modules and private names.
            continue
        new = old
        if old.startswith('EVT_'):
            # Leave name unmodified; add to the new wx namespace.
            d_new[new] = obj
        elif old.startswith('wxEVT_'):
            # Leave name unmodified; add to the new wx namespace.
            d_new[new] = obj
        else:
            if old.startswith('wx'):
                # Remove the 'wx' prefix.
                new = old[2:]
            # Add to the new wx package namespace.
            d_new[new] = obj

    del d_new
    del d_old
    del new
    del obj
    del old
    del types

    del wx

Namespaces in Python are implemented as dictionaries. The dictionary used to create the wx package's namespace is accessible using the `globals()` function. The dictionary used to create the old wxPython.wx module's namespace is `wx.__dict__`. Once we have these two dictionaries, it's a simple matter of iterating through one, changing the names, adding the renamed object to the other dictionary, and cleaning up a few local variables and imported modules. Voila!

# What about all the other modules, like grid, html, and stc?

There's more to wxPython than just the wx namespace. And we've got those extra modules covered as well. For each of those modules (as well as the lib package) we've got matching modules in the new wx package. Let's take a look at a few of them.

Here is `html.py`:

    """Provides a way to drop the wx prefix from wxPython objects."""

    __author__ = "Patrick K. O'Brien <pobrien@orbtech.com>"
    __cvsid__ = "$Id: wxPackage.html,v 1.1.2.1 2003/06/05 23:18:13 RD Exp $"
    __revision__ = "$Revision: 1.1.2.1 $"[11:-2]

    import wx
    from wx import prefix

    from wxPython import html
    prefix.rename(d_new=globals(), d_old=html.__dict__)
    del html

    del prefix
    del wx

And here is `lib/dialogs.py`:

    """Provides a way to drop the wx prefix from wxPython objects."""

    __author__ = "Patrick K. O'Brien <pobrien@orbtech.com>"
    __cvsid__ = "$Id: wxPackage.html,v 1.1.2.1 2003/06/05 23:18:13 RD Exp $"
    __revision__ = "$Revision: 1.1.2.1 $"[11:-2]

    import wx
    from wx import prefix

    from wxPython.lib import dialogs
    prefix.rename(d_new=globals(), d_old=dialogs.__dict__)
    del dialogs

    del prefix
    del wx

As you can see, they both rely on the `prefix.rename()` function defined in `prefix.py`:

    """Renaming utility.

    Provides a way to drop the wx prefix from wxPython objects."""

    __author__ = "Patrick K. O'Brien <pobrien@orbtech.com>"
    __cvsid__ = "$Id: wxPackage.html,v 1.1.2.1 2003/06/05 23:18:13 RD Exp $"
    __revision__ = "$Revision: 1.1.2.1 $"[11:-2]

    import types

    def rename(d_new, d_old):
        for old, obj in d_old.items():
            if type(obj) is types.ModuleType or old.startswith('_'):
                # Skip modules and private names.
                continue
    ##         mod = d_old['__name__']
    ##         if hasattr(obj, '__module__') and not obj.__module__.startswith(mod):
    ##             # Skip objects imported from other modules, except those
    ##             # related to the current module, such as stc_.
    ##             continue
            new = old
            if old.startswith('EVT_') or old.startswith('wxEVT_'):
                # Leave these names unmodified.
                pass
            elif old.startswith('wx'):
                new = old[2:]
            if new:
                d_new[new] = d_old[old]

Again, the technique is very similar to the one used by the wx package.

# How do I use this new wx package?

The wx package is automatically created when you install wxPython version 2.4.1 or higher. So all you have to do is:

    import wx

# What are the issues with converting old code to use the new wx package?

Obviously, you need to change your import statements from:

    from wxPython import wx

or:

    from wxPython.wx import *

to:

    import wx

Then you need to refer to wx attributes without a "wx" prefix, such as:

    class MyFrame(wx.Frame):

In most cases, existing code can be modified with a simple search and replace.

One extra issue you might run into when converting existing code is that the wx.__version__ attribute is no longer available, since the new wx namespace doesn't include any private attributes from the old wxPython.wx namespace. The solution is to use the wx.VERSION_STRING attribute, which was introduced in wxPython 2.4.1.

# Where can I find example programs using the new wx syntax?

Example programs are included in the wxPython/samples/wx_examples directory, and are documented in the wxPythonExamples documentation file. Also, all the code in the py package uses the new wx syntax. You can learn more about these in the PyManual.