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    <p>For ease of use, <a href="http://docs.python.org/library/ctypes.html" rel="noreferrer">ctypes</a> is the way to go.</p> <p>The following example of ctypes is from actual code I've written (in Python 2.5). This has been, by far, the easiest way I've found for doing what you ask.</p> <pre><code>import ctypes # Load DLL into memory. hllDll = ctypes.WinDLL ("c:\\PComm\\ehlapi32.dll") # Set up prototype and parameters for the desired function call. # HLLAPI hllApiProto = ctypes.WINFUNCTYPE ( ctypes.c_int, # Return type. ctypes.c_void_p, # Parameters 1 ... ctypes.c_void_p, ctypes.c_void_p, ctypes.c_void_p) # ... thru 4. hllApiParams = (1, "p1", 0), (1, "p2", 0), (1, "p3",0), (1, "p4",0), # Actually map the call ("HLLAPI(...)") to a Python name. hllApi = hllApiProto (("HLLAPI", hllDll), hllApiParams) # This is how you can actually call the DLL function. # Set up the variables and call the Python name with them. p1 = ctypes.c_int (1) p2 = ctypes.c_char_p (sessionVar) p3 = ctypes.c_int (1) p4 = ctypes.c_int (0) hllApi (ctypes.byref (p1), p2, ctypes.byref (p3), ctypes.byref (p4)) </code></pre> <p>The <code>ctypes</code> stuff has all the C-type data types (<code>int</code>, <code>char</code>, <code>short</code>, <code>void*</code>, and so on) and can pass by value or reference. It can also return specific data types although my example doesn't do that (the HLL API returns values by modifying a variable passed by reference).</p> <hr> <p>In terms of the specific example shown above, IBM's EHLLAPI is a fairly consistent interface.</p> <p>All calls pass four void pointers (EHLLAPI sends the return code back through the fourth parameter, a pointer to an <code>int</code> so, while I specify <code>int</code> as the return type, I can safely ignore it) as per IBM's documentation <a href="http://publib.boulder.ibm.com/infocenter/pcomhelp/v5r9/index.jsp?topic=/com.ibm.pcomm.doc/books/html/emulator_programming08.htm" rel="noreferrer">here</a>. In other words, the C variant of the function would be:</p> <pre><code>int hllApi (void *p1, void *p2, void *p3, void *p4) </code></pre> <p>This makes for a single, simple <code>ctypes</code> function able to do anything the EHLLAPI library provides, but it's likely that other libraries will need a separate <code>ctypes</code> function set up per library function.</p> <p>The return value from <code>WINFUNCTYPE</code> is a function prototype but you still have to set up more parameter information (over and above the types). Each tuple in <code>hllApiParams</code> has a parameter "direction" (1 = input, 2 = output and so on), a parameter name and a default value - see the <code>ctypes</code> doco for details</p> <p>Once you have the prototype and parameter information, you can create a Python "callable" <code>hllApi</code> with which to call the function. You simply create the needed variable (<code>p1</code> through <code>p4</code> in my case) and call the function with them.</p>
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    1. POHow can I use a DLL file from Python?
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    1. POHow can I use a DLL file from Python?
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    1. COYep, ctypes is great. Python has been blessed with a great built-in (since 2.5) way to access code in DLLs. ctypes is so easy to use that you have to think twice before writing real extensions, instead of just providing a pure Python module that uses ctypes to interface your DLL.
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      1. USEli Bendersky
    2. COHello, it may be a long time since someone replied here but I wanted to know something to make this work exactly for my program. Could you tell me what is "HLLAPI" in this? Also, if I want to access my dll with a function "void BoxProperties(double L, double H, double W,double &A, double &V);" could you suggest me what changes should I make to the above code in order to make it work? Cheers.
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    3. COWhat exactly does `hllApiParams` do? What is the point of those tuples? It's hard to match up some of the things in this example with the documentation.
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      1. USJonathon Reinhart
 

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