first_class.py

def compose(f1, f2):
    return lambda x: f1(f2(x))

second_class.c

/* declare a typedef for a function pointer */
typedef double (*Class2Func)(double);

typedef struct sComposition {
   Class2Func f1;
   Class2Func f2;
} *Composition;

Composition Compose( Class2Func f1, Class2Func f2)
{
   Composition comp = malloc(sizeof(struct sComposition));
   comp->f1 = f1;
   comp->f2 = f2;
   return comp;
}

double CallComposed( Composition comp, double val )
{
    return comp->f1( comp->f2(val) );
}