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From: Grant Edwards on 8 Jul 2010 15:55

I'm playign with Python bindings for libconfig, and one of the methods
does something that seems very odd to me. The purpose of the method
is to fetch the value found a a particular path within the
configuration namespace.

If the path exists and has a scalar value the method returns the tuple
(<value>,True). Otherwise it returns ('',False). AFAICT, the latter
happens in either of two cases: the path doesn't exist at all, or the
path exists but doesn't have a scalar value (it's an aggretate object
such as a list, group, or array).

This seems distinctly un-pythonic.

I would think that the right thing to do would be to either return the
requested value or raise an exception. The libconfig C++ API defines
a "SettingNotFound" exception and "SettingTypeException" that seem
appropriate in the two failure cases.

Is there something about implementing bindings using Boost that makes
this sort of (<value>,<success>) return tuple a desirable way to do
things?

FWIW, here's the method I find puzzling:

tuple value ( const char * path )
{
std::string v_string;
if ( config->lookupValue ( path, v_string ) )
return make_tuple ( v_string.c_str(), true );

unsigned int v_uint;
if ( config->lookupValue ( path, v_uint ) )
return make_tuple ( v_uint, true );

int v_int;
if ( config->lookupValue ( path, v_int ) )
return make_tuple ( v_int, true );

bool v_bool;
if ( config->lookupValue ( path, v_bool ) )
return make_tuple ( v_bool, true );

unsigned long long v_ulonglong;
if ( config->lookupValue ( path, v_ulonglong ) )
return make_tuple ( v_ulonglong, true );

long long v_longlong;
if ( config->lookupValue ( path, v_longlong ) )
return make_tuple ( v_longlong, true );

float v_float;
if ( config->lookupValue ( path, v_float ) )
return make_tuple ( v_float, true );

double v_double;
if ( config->lookupValue ( path, v_double ) )
return make_tuple ( v_double, true );

return make_tuple ( "", false );
}





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