How to split a function into separate components (according to their variables)?

edit

Is there a way to find, for example, f_x1=10*x1+5*x1^2 for the following f?

f = 10*x1 + 20*x2 + 10*y1 + 10*y2 + 5*x1^2 - 7*x2^6

Thank you........ I thought the operand() method identified only factors rather than general elements of an expression. I would also like to see if there's an answer to tolga's question too.....

The following is a way to get the parts for a given variable:

def dependentpart(f, val):
    terms = f.operands()
    mypart = sum(item for item in terms if item.has(val))
    return mypart

x1, x2, y1, y2 = var("x1, x2, y1, y2")

f = 10*x1 + 20*x2 + 10*y1 + 10*y2 + 5*x1^2 - 7*x2^6

f_x1=dependentpart(f,x1)
f_x2=dependentpart(f,x2)
f_y1=dependentpart(f,y1)
f_y2=dependentpart(f,y2)

show(f_x1)
show(f_x2)
show(f_y1)
show(f_y2)

Also, check the following:

def dependentpart(f, val):
    terms = f.operands()
    mypart = sum(item for item in terms if item.has(val))
    return mypart

x1, x2, y1, y2 = var("x1, x2, y1, y2")

f = 10*x1 + 20*x2 + 10*y1 + 10*y2 + 5*x1^2 - 7*x2^6

myvars = f.variables()
forallvars=[dependentpart(f, val) for val in myvars]
show(forallvars)