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POImplementing C's enum and union in python
 

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    <p>I'm trying to figure out some C code so that I can port it into python. The code is for reading a proprietary binary data file format. It has been straightforward thus far -- it's mainly been structs and I have been using the <code>struct</code> library to ask for particular ctypes from the file. However, I just came up on this bit of code and I'm at a loss for how to implement it in python. In particular, I'm not sure how to deal with the <code>enum</code> or the <code>union</code>.</p> <pre><code>#define BYTE char #define UBYTE unsigned char #define WORD short #define UWORD unsigned short typedef enum { TEEG_EVENT_TAB1=1, TEEG_EVENT_TAB2=2 } TEEG_TYPE; typedef struct { TEEG_TYPE Teeg; long Size; union { void *Ptr; // Memory pointer long Offset }; } TEEG; </code></pre> <p>Secondly, in the below struct definition, I'm not sure what the colons after the variable names mean, (e.g., <code>KeyPad:4</code>). Does it mean I'm supposed to read 4 bytes?</p> <pre><code>typedef struct { UWORD StimType; UBYTE KeyBoard; UBYTE KeyPad:4; UBYTE Accept:4; long Offset; } EVENT1; </code></pre> <p>In case it's useful, an abstract example of the way I've been accessing the file in python is as follows:</p> <pre> from struct import unpack, calcsize def get(ctype, size=1): """Reads and unpacks binary data into the desired ctype.""" if size == 1: size = '' else: size = str(size) chunk = file.read(calcsize(size + ctype)) return unpack(size + ctype, chunk)[0] file = open("file.bin", "rb") file.seek(1234) var1 = get('i') var2 = get('4l') var3 = get('10s') </pre>
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    1. COSince I don't really know python, I can't help you there, but the colons after the variable name indicate howmany Bits are used to store it (so keyPad and Accept share a byte, KeyPad residing in its first four bits, Accept in the last four)
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    2. COUnions aren't necessary in Python since it doesn't use strict type checking. In your case above, you can bind both the address to an object, and a long to the same name.
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    3. CO@Micael Mior. Python __does__ do strict type checking - at run time. While you can bind an two different values to the same name, you can never have them __share the same address__ which is what union in C does.
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