I am trying to make a part of my following code to work but so far I haven't been successful... I have 1 tree file with several branches but the two I care about are named Trigger and Variable. I have calculated in two histograms h(Variable) the weights I want to obtain. My function that I am trying to run is supposed to return me the weight of the given Variable value and Trigger (takes values 1 or 2). Code (Python): def return_weight(tree, histo_list, branches_list): #tree containing the variables in branches #histo_list = [histo_triggerPass(Variable), histo_triggerFail(Variable) ] #branches_list = [Variable, Trigger] Variable_val = getattr( tree , branches_list) Trigger_pass= getattr( tree, branches_list) #Problem is supposed to be HERE ^ print Variable_val, " \t ", Trigger_pass if Trigger_pass==1: ... else: ... The printing output is telling me that the Variable_val is obtained correctly from the tree, but the Trigger_pass is not (it somehow always returns 0). Any help?