[Tutor] Accessing a DLL from python
Hanlie Pretorius
hanlie.pretorius at gmail.com
Tue Mar 1 10:21:37 CET 2011
Hi Python Tutors,
I'm using a storm water modelling program, EPA SWMM, to model the
hydrology and hydraulics of a study area.
SWMM reports its results in a binary (.out) file that contains the
results for each element in the model at each time step in the model
run. According to the SWMM interface manual
(http://www.epa.gov/ednnrmrl/models/swmm/swmm5_iface.zip), one can use
a DLL file to read the .out file. I want to do this so that I can read
the state of a river at a specific time and plot its water level in a
GIS.
After some searching on the Internet, I came across ctypes, which I
have tried. According to the SWMM manual:
[manual]
Opening the Output File
----------------------------------
A function named OpenSwmmOutFile(outFile) that performs these tasks is
contained in the example code files that accompany this guide. The
argument to the function is the name of the binary output file. The
return value from the function is an integer code with the following
meanings:
0 - the run was successful
1 - the run was terminated with an error
2 - the output file could not be opened.
[/manual]
So, I tried the following python code:
[code]
In [14]: swmmdll = cdll.LoadLibrary("C:\\Hanlie\\model\\SWMM\\swmm5_0_018.dll")
In [15]: results_file="C:\\Hanlie\\model\\SWMM\\c83a_v0\\c83a_v0.3.out"
In [16]: open_file=swmmdll.OpenSwmmOutFile(results_file)
------------------------------------------------------------
Traceback (most recent call last):
File "<ipython console>", line 1, in <module>
File "C:\Python26\lib\ctypes\__init__.py", line 366, in __getattr__
func = self.__getitem__(name)
File "C:\Python26\lib\ctypes\__init__.py", line 371, in __getitem__
func = self._FuncPtr((name_or_ordinal, self))
AttributeError: function 'OpenSwmmOutFile' not found
[/code]
Can anyone perhaps help me to access the functions in this DLL?
The manual also states:
[manual]
The following files are needed for applications that call functions
from the swmm5.dll library:
· swmm5.h for C/C++ applications
· swmm5.bas for Visual Basic applications
· swmm5.pas for Delphi applications.
[/manual]
And they give an example in C, Basic and Pascal to use the interface.
I have appended the C example to this message.
Thanks
Hanlie
[code]
// swmm5_iface.c
//
// Example code for interfacing SWMM 5 with C/C++ programs.
//
// Remember to #include the file swmm5_iface.h in the calling program.
#include <stdio.h>
#include <windows.h>
#include "swmm5.h"
int SWMM_Nperiods; // number of reporting periods
int SWMM_FlowUnits; // flow units code
int SWMM_Nsubcatch; // number of subcatchments
int SWMM_Nnodes; // number of drainage system nodes
int SWMM_Nlinks; // number of drainage system links
int SWMM_Npolluts; // number of pollutants tracked
double SWMM_StartDate; // start date of simulation
int SWMM_ReportStep; // reporting time step (seconds)
int RunSwmmExe(char* cmdLine);
int RunSwmmDll(char* inpFile, char* rptFile, char* outFile);
int OpenSwmmOutFile(char* outFile);
int GetSwmmResult(int iType, int iIndex, int vIndex, int period,
float* value);
void CloseSwmmOutFile(void);
static const int SUBCATCH = 0;
static const int NODE = 1;
static const int LINK = 2;
static const int SYS = 3;
static const int RECORDSIZE = 4; // number of bytes per file record
static int SubcatchVars; // number of subcatch reporting variables
static int NodeVars; // number of node reporting variables
static int LinkVars; // number of link reporting variables
static int SysVars; // number of system reporting variables
static FILE* Fout; // file handle
static int StartPos; // file position where results start
static int BytesPerPeriod; // bytes used for results in each period
static void ProcessMessages(void);
//-----------------------------------------------------------------------------
int RunSwmmExe(char* cmdLine)
//-----------------------------------------------------------------------------
{
int exitCode;
STARTUPINFO si;
PROCESS_INFORMATION pi;
// --- initialize data structures
memset(&si, 0, sizeof(si));
memset(&pi, 0, sizeof(pi));
si.cb = sizeof(si);
si.wShowWindow = SW_SHOWNORMAL;
// --- launch swmm5.exe
exitCode = CreateProcess(NULL, cmdLine, NULL, NULL, 0,
0, NULL, NULL, &si, &pi);
// --- wait for program to end
exitCode = WaitForSingleObject(pi.hProcess, INFINITE);
// --- retrieve the error code produced by the program
GetExitCodeProcess(pi.hProcess, &exitCode);
// --- release handles
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
return exitCode;
}
//-----------------------------------------------------------------------------
int RunSwmmDll(char* inpFile, char* rptFile, char* outFile)
//-----------------------------------------------------------------------------
{
int err;
double elapsedTime;
// --- open a SWMM project
err = swmm_open(inpFile, rptFile, outFile);
if (!err)
{
// --- initialize all processing systems
err = swmm_start(1);
if (err == 0)
{
// --- step through the simulation
do
{
// --- allow Windows to process any pending events
ProcessMessages();
// --- extend the simulation by one routing time step
err = swmm_step(&elapsedTime);
/////////////////////////////////////////////
// --- call progress reporting function here,
// using elapsedTime as an argument
/////////////////////////////////////////////
} while (elapsedTime > 0.0 && err == 0);
// --- close all processing systems
swmm_end();
}
}
// --- close the project
swmm_close();
return err;
}
//-----------------------------------------------------------------------------
void ProcessMessages(void)
//-----------------------------------------------------------------------------
{
/**** Only use this function with a Win32 application *****
MSG msg;
while (TRUE)
{
if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
{
if (msg.message == WM_QUIT) break;
else
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
else break;
}
***********************************************************/
}
//-----------------------------------------------------------------------------
int OpenSwmmOutFile(char* outFile)
//-----------------------------------------------------------------------------
{
int magic1, magic2, errCode, offset, offset0, version;
int err;
// --- open the output file
Fout = fopen(outFile, "rb");
if (Fout == NULL) return 2;
// --- check that file contains at least 14 records
fseek(Fout, 0L, SEEK_END);
if (ftell(Fout) < 14*RECORDSIZE)
{
fclose(Fout);
return 1;
}
// --- read parameters from end of file
fseek(Fout, -5*RECORDSIZE, SEEK_END);
fread(&offset0, RECORDSIZE, 1, Fout);
fread(&StartPos, RECORDSIZE, 1, Fout);
fread(&SWMM_Nperiods, RECORDSIZE, 1, Fout);
fread(&errCode, RECORDSIZE, 1, Fout);
fread(&magic2, RECORDSIZE, 1, Fout);
// --- read magic number from beginning of file
fseek(Fout, 0L, SEEK_SET);
fread(&magic1, RECORDSIZE, 1, Fout);
// --- perform error checks
if (magic1 != magic2) err = 1;
else if (errCode != 0) err = 1;
else if (SWMM_Nperiods == 0) err = 1;
else err = 0;
// --- quit if errors found
if (err > 0 )
{
fclose(Fout);
Fout = NULL;
return err;
}
// --- otherwise read additional parameters from start of file
fread(&version, RECORDSIZE, 1, Fout);
fread(&SWMM_FlowUnits, RECORDSIZE, 1, Fout);
fread(&SWMM_Nsubcatch, RECORDSIZE, 1, Fout);
fread(&SWMM_Nnodes, RECORDSIZE, 1, Fout);
fread(&SWMM_Nlinks, RECORDSIZE, 1, Fout);
fread(&SWMM_Npolluts, RECORDSIZE, 1, Fout);
// Skip over saved subcatch/node/link input values
offset = (SWMM_Nsubcatch+2) * RECORDSIZE // Subcatchment area
+ (3*SWMM_Nnodes+4) * RECORDSIZE // Node type, invert & max depth
+ (5*SWMM_Nlinks+6) * RECORDSIZE; // Link type, z1, z2,
max depth & length
offset = offset0 + offset;
fseek(Fout, offset, SEEK_SET);
// Read number & codes of computed variables
fread(&SubcatchVars, RECORDSIZE, 1, Fout); // # Subcatch variables
fseek(Fout, SubcatchVars*RECORDSIZE, SEEK_CUR);
fread(&NodeVars, RECORDSIZE, 1, Fout); // # Node variables
fseek(Fout, NodeVars*RECORDSIZE, SEEK_CUR);
fread(&LinkVars, RECORDSIZE, 1, Fout); // # Link variables
fseek(Fout, LinkVars*RECORDSIZE, SEEK_CUR);
fread(&SysVars, RECORDSIZE, 1, Fout); // # System variables
// --- read data just before start of output results
offset = StartPos - 3*RECORDSIZE;
fseek(Fout, offset, SEEK_SET);
fread(&SWMM_StartDate, sizeof(double), 1, Fout);
fread(&SWMM_ReportStep, RECORDSIZE, 1, Fout);
// --- compute number of bytes of results values used per time period
BytesPerPeriod = 2*RECORDSIZE + // date value (a double)
(SWMM_Nsubcatch*SubcatchVars +
SWMM_Nnodes*NodeVars+
SWMM_Nlinks*LinkVars +
SysVars)*RECORDSIZE;
// --- return with file left open
return err;
}
//-----------------------------------------------------------------------------
int GetSwmmResult(int iType, int iIndex, int vIndex, int period, float* value)
//-----------------------------------------------------------------------------
{
int offset;
// --- compute offset into output file
*value = 0.0;
offset = StartPos + (period-1)*BytesPerPeriod + 2*RECORDSIZE;
if ( iType == SUBCATCH )
{
offset += RECORDSIZE*(iIndex*SubcatchVars + vIndex);
}
else if (iType == NODE)
{
offset += RECORDSIZE*(SWMM_Nsubcatch*SubcatchVars +
iIndex*NodeVars + vIndex);
}
else if (iType == LINK)
{
offset += RECORDSIZE*(SWMM_Nsubcatch*SubcatchVars +
SWMM_Nnodes*NodeVars +
iIndex*LinkVars + vIndex);
}
else if (iType == SYS)
{
offset += RECORDSIZE*(SWMM_Nsubcatch*SubcatchVars +
SWMM_Nnodes*NodeVars +
SWMM_Nlinks*LinkVars + vIndex);
}
else return 0;
// --- re-position the file and read the result
fseek(Fout, offset, SEEK_SET);
fread(value, RECORDSIZE, 1, Fout);
return 1;
}
//-----------------------------------------------------------------------------
void CloseSwmmOutFile(void)
//-----------------------------------------------------------------------------
{
if (Fout != NULL)
{
fclose(Fout);
Fout = NULL;
}
}
[/code]
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