Q:

How to append float to a list inside a dictionary

a challenge for a Python beginner such as I, I need to create objects which contain dictionary of lists of floating number values. I tried this flow, the objects seem to be created online, but the code stops on the line in which I try to append more values to an object that was already created, telling me that :

AttributeError: 'float' object has no attribute 'append'

This is the piece of code I'm using for this mission:
class Wimp(object):
    def __init__(self, mass, definitions):
        self.mass = mass
        self.dN_dx = {}
        for definition in definitions:
            self.dN_dx[definition] = []
            print definition, "added"
        print "Wimp of mass", self.mass, "created."

wimp_data = {}

i=0
    for mass in nu_e_mass:
        if mass == nu_e_mass[i+1]:
            #Saving the columns into arrays
            if mass not in wimp_data:
                wimp_data[mass] = Wimp(mass, definitions)
                for j in range(1, len(definitions)):
                    wimp_data[mass].dN_dx[definitions[j]] = float(nu_e[j][i])
            else:
                for j in range(1, len(definitions)):
                    wimp_data[mass].dN_dx[definitions[j]].append(nu_e[j][i])
            #print mass, "Same mass", nu_e_mass[i+1]
            if i < (len(nu_e_mass)-2):
                i = i+1
        else:
            #Integrating the columns and storing into Wimp class
            #print mass, "Skipping to next mass",  i, nu_e_mass[i+1]
            i = i+1

If someone can spot the error it would be great as I am gazing on this code for hours now..

A:

Seems like you are defining the element as a float, not a list, in the first for loop:
wimp_data[mass].dN_dx[definitions[j]] = float(nu_e[j][i])

So naturally you can't append to it in the second one. Maybe you meant to make it a list containing a single float:
wimp_data[mass].dN_dx[definitions[j]] = [float(nu_e[j][i])]

