Binary vs. Non-Binary Trees

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But before I get back to scripting issues, one brief correction. An attentive reader noted that "The Well-Tempered Clavier" was in fact designed to sound good on a "well tempered" instrument, not an "equally tempered" instrument. The difference is that a "well" temperament is designed so that every key sounds good, but is allowed to have some badly-out-of-tune intervals that must be avoided. Traditionally these are called "wolf intervals".

There was considerable controversy when equal temperament was introduced in Europe. I suppose it was the "what is the One True Bracing Style? Another commenter pointed out that you could translate my wav-writing binary files and the file system object do not mix fabulous adventures in coding into VBScript by using the File System Object to write out the bytes.

To simplify their code down to a program that writes out individual bytes:. Write Chr i Next File. Please don't do that. See that line that says binary files and the file system object do not mix fabulous adventures in coding We wrote that method to create a text filenot a binary file.

Though this code might appear to work, it actually does not. Text files are more than just binary files that can be interpreted as text. Text files have to conform to certain rules to ensure that they can be sensibly interpreted as text in the local code page. If you said "it writes out a binary file consisting of E0 bytes," bzzt! In the Japanese code page, just-plain-chr E0 is not even a legal characterso Chr will turn it into a zero.

If I were whipping up a little one-off program on my own to write out a binary file -- well, I'd personally do it in C, but I can see how some people might want to do it in script.

But there's a big difference between writing a one-off program that you're going to delete in five minutes, and writing a general-purpose utility program that you expect people around the world will use.

I have been asked many times over the years if I know of a scriptable object that can read-write true binary files in all locales. Anyone have any suggestions? I would have thought given the number of people that have asked me, that some third party would have come up with something decent by now. I have never had to deal with that. How do you create the binary array?

VBScript only supports creation of arrays of variants. I found that text mode works OK like so. Only for writing, though. There still is a problem when you try to read some of the byte values 0x80 — 0x9f: I guess this also relates to encoding. We certainly considered it.

However, there are two main factors. First, and most important, we decided that the Script Team wanted to be in the business of building the script engines themselves, not the objects that those engines would script. So we finished off the FSO and called it done. This also explains why we did not add any features to the WScript. Network object, etc, when we inherited the WSH codebase. Exposing a straightforward array of bytes on disk is only the very first step. But once you bite that off — big endian or little endian?

How do you handle seeking? What if the user is reading a file that has a DBCS string embedded in it and wants to translate it into a Unicode string?

You have to think about the real-world problems that people are going to have to solve with this tool, and there are a LOT of different scenarios for binary files. Recordset is quite popular in… certain communities. To do it right and make it usable,… ". Another, quite simple approach, is to NOT be the end-all and just support reading and writing a series of bytes. As it is now, I seem to be left with a choice of: Neither is a good solution.

Why is this such a big deal MS?? In VBScript there is no way to create a byte array. VBScript only supports arrays of variants. In VBScript if you create a string that contains binary data, and then pass that to an ActiveX object which expects a byte array, the default implementation of IDispatch:: Invoke provided by the operating system will turn the binary files and the file system object do not mix fabulous adventures in coding string into a byte array for you.

So maybe that sneaky trick will work for you. Eric, you mentioned that creating a string that contains binary data would satisfy a COM method that expects a byte array. That is exactly what I am seeking. Could you please give an example of code that would create such string from a conventional VBScript string, say, "Hello World"?

Stream object mentioned above, which resolved the problem I had. Consider the following snippet I recently wrote to update a database connection UDL file:. Everything except the most basic of basic text files that do not include any currency symbols other than the dollar sign.

It seems to have great support for Binary files. Instead of using ReadAll just use recursice Read to the file Size. Streams for most of my binary file ops already. The fso seems to happily, and binarily, write your binary file without hesitation. The code described in [ http: OK, back binary files and the file system object do not mix fabulous adventures in coding scripting today. To simplify their code down to a program that writes out individual bytes: Close And sure enough, this writes out a binary file consisting of those bytes.

Let me give you an example that clearly fails. What does this program do? Close If you said "it writes out a binary file consisting of E0 bytes," bzzt! April 20, at 1: April 20, at 2: April 20, at 4: April 20, at 7: April 21, at 9: April 21, at April 22, at 2: April 22, at 6: April 24, at 8: April 26, at 1: May 12, at February 4, at 3: March 5, at 4: March 23, at March 23, at 1: March 24, at March 27, at 3: July 11, at 7: March 14, at April 24, at 9: May 17, at 3: May 24, at October 16, at 1: February 11, at April 28, at 5: July 16, at 4: May 11, at 6: November 18, at 2: March 29, at 7:

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Here at Dropbox, we often use Python in uncommon ways. This module allows you to write COM-compatible code using only Python.

For example, the Dropbox desktop client feature that allows you to upload photos from a camera uses comtypes to access Windows Autoplay. But before we talk about comtypes, we have to talk about COM. The Component Object Model is a standard introduced by Microsoft back in It allows two software components to interact without either one having knowledge of how the other is implemented, even if the components are written in different languages, running in different processes, or running on different machines and different platforms.

And it does all this using a standard that was created almost 20 years ago. On Windows, COM is both a standard and a service. It provides all the systems and utilities necessary to make inter-component compatibility possible.

The standard requires interfaces to be compiled into a binary format that is language agnostic. For this purpose, it includes a specification for its own interface language—the Microsoft Interface Definition Language, aka MIDL—which is compiled into a binary called a type library that is then included inside a runnable such as a. Well, parlez-vous version 1? COM handles these things for you, but this functionality comes at a cost.

It involves a fair amount of complexity, which is unfortunately necessary, and a lot of syntactic convolution, which is just plain unfortunate.

COM requires incantations such as. To ensure unambiguity in class and interface identification, everything is referenced by GUIDs, which are undescriptive and unwieldy at best. And when creating a COM server, the sheer number of configuration options at every step of the way can be paralyzing. I came to Dropbox with enough knowledge of COM to squeak by, and still consider myself no more than an advanced novice. If one were to attempt to write pure Python code that used or, heaven forbid, implemented a COM object, one would need to generate and parse the binary type library files that specify COM interfaces, perform all the complex Windows registry rituals, track all the reference counts to COM objects, as well as correctly write the endless syntactical mumbo jumbo.

Fortunately for us, the comtypes module exists to abstract almost all of this horribleness away from us. If COM is black magic, then comtypes is the mysterious witch doctor service that you contract to perform the black magic for you. For simple tasks, everything likely works fine. Unfortunately, if you need to do anything very complex, you run the risk of being left in the dark as to what sort of invocations were performed, only to find the demon knocking on your door.

Still, comtypes makes life much easier. This slightly simplified sample code allows access to the contents of a camera attached to the computer. The deviceobj is a Python wrapper around a COM object that is actually implemented elsewhere on the system, one that represents a camera we can interface with.

Underneath, comtypes will be busy CoCreateInstancing, QueryInterfacing, and wrapping ctypes objects with Python objects for your ease of use. The magic begins in the comtypes.

The handy helper function GetModule will take a binary file like a. It is declared as two mystery types followed by three 32 bit ints.

Further digging will reveal that one of the unknown types is an enum, but the other is another struct involving more unknown types. For it to be usable in Python, you have to break things down into known types without the benefit of importing hundreds of Windows headers.

GetModule will do all of these things for you, but the generated code hides the interesting part, the wrapper classes that actually proxy to the real COM objects underneath. In COM, IUnknown is the grandfather of all interfaces, the interface which all other interfaces inherit from. It contains only three functions:. In comtypes land, IUnknown is actually a base class. The class IUnknown itself is actually pretty simple. For the uninitiated, all Python classes are actually objects, and metaclasses are things that make classes.

Open , which takes in two parameters and returns nothing; and IPortableDevice. Content , which takes no parameters and returns one. The wrappers then proxy the method calls into an actual COM object that was instantiated under the covers, wrap the return values in Python types, and return them to you, transforming returned error codes into Python exceptions along the way. The most painful such incident brought development to a dead halt for two days.

The only symptom was that the program would occasionally crash after reading a bunch of images from a camera. The bug was non-deterministic and no exception was generated. After endless hours of printing and prodding, I finally found the root cause of the problem. Additional calls to AddRef and Release are only necessary if the user makes copies of the reference to the object.

This in itself is only passingly strange, because it usually works. However, the clever wrapping of COM objects sometimes results in comtypes objects being created unexpectedly, and then also deleted unexpectedly.

For example, in the following code. In the process, it unexpectedly creates an instance of IDeviceItem. More importantly, it unexpectedly destroys an instance of IDeviceItem.

So, the following code. After the first Release call, the COM object is considered deleted. Whenever the garbage collector for that COM object is triggered, everything explodes. Save your reference into a Python object and keep it around. This results in exactly one call to Release , which occurs when the Python object deviceitem is destroyed. All of this happened within my first few months at Dropbox, and I barely spoke Python at the time.

I learned what a metaclass was before I had fully mastered list slicing syntax. Meanwhile, my counterpart on the Mac camera uploads side was not having the easiest time either. It made me feel a little bit better about dealing with incorrect vtable pointers and bad reference counting.

Discovering comtypes was an integral part of the development of the photo feature, and it certainly presented enough excitement to be considered an adventure. Reference counting bugs are the price you pay when you work with low-level code, but it certainly would have been much more work to write our own Python wrappers around COM. COM may be difficult to use, and comtypes occasionally frustrating, but with a working knowledge of how to use the first and how to work around unexpected pitfalls in the second, we can plow ahead with future Windows features.

In fact, not long after we released the camera feature, we found ourselves again needing to interact with a COM component. With all this knowledge under my hat, I made myself a COM client in no time. It was a glorious victory. Hi — great article! This article just reminds of the nightmares that used to be. I still think in COM sometimes, I loved working with it.

COM is possibly one of the worst psuedo technologies that ever existed. And the reason why it existed was to obfuscate programming windows. As a technology COM itself is a spectacular failure. SO spectacular that MS has done nothing but try and paper over it again and again as if we wont notice its there. COM is designed to solve binary compatibility between modules implemented on different programming languages.

This you cannot get directly with plain C. The concepts it has are SAME as you would find in any similar technology and are not bound to any particular programming language. COM is there to stay. It is all over Windows and it does its job well. If you wanted to solve same problem that COM solves, your solution would not be much different.

Just when you think you understand COM this book will whack you in the head and show you how little you really know. In COM, objects are created and destroyed and objects implement interfaces, e. Actually it says a bit earlier in the article that on the Python side, IDeviceItem is a class.

Skip to content Here at Dropbox, we often use Python in uncommon ways. Comtypes If COM is black magic, then comtypes is the mysterious witch doctor service that you contract to perform the black magic for you. Content for item in contents: GetModule The magic begins in the comtypes.

It contains only three functions: So, the following code for i in range Microsoft rules specify that the beard requirement can be waived if you wear a tie. Takes me back… Now to try and forget before the nightmares set in Like Like. Ive been MS dev tool free for 10 years now, and Ill never go back.