Iterate through subsets of a dataframe

Question

This is my first time posting on here. I have the code below that should loop through the energies in this dataframe and output the associated cross sections from the energy that falls within that range. However when I print out the cross-sections within the if statement, it prints out all the values in the energy dataframe, rather than a small subset. It should return only 120 cross section values in the end, not just one, as it does now. Does anyone know how I can fix this?

energy = df.x #pandas dataframe

def crosssection(energy): 
    for i in energy: 
        if [(i >= .284) & (i <.400)]:
            c0, c1, c2 = 78.1, 18.8, 4.3
            cross_section = (c0 + c1*i + c2*i**2)*(i**-3)*10**-24
            print(i)
            print(cross_section)
        elif [(i >= .400) & (i <.532)]:
            c0, c1, c2 = 71.4, 66.8, -51.4
            cross_section = (c0 + c1*i + c2*i**2)*(i**-3)*10**-24
            
        elif [(i >= .532) & (i <.707)]:
            c0, c1, c2 = 95.5, 145.8, -61.1
            cross_section = (c0 + c1*i + c2*i**2)*(i**-3)*10**-24

        elif [(i >= .707) & (i <.867)]:
            c0, c1, c2 = 308.9, -380.6, 294.0
            cross_section = (c0 + c1*i + c2*i**2)*(i**-3)*10**-24

        elif [(i >= .867) & (i <1.303)]:
            c0, c1, c3 = 120.6, 169.3, -47.7
            cross_section = (c0 + c1*i + c2*i**2)*(i**-3)*10**-24

        elif [(i >= 1.303) & (i <1.840)]:
            c0, c1, c3 = 141.3, 146.8, -31.5
            cross_section = (c0 + c1*i + c2*i**2)*(i**-3)*10**-24

        elif [(i >= 1.840) & (i <2.471)]:
            c0, c1, c3 = 202.7, 104.7, -17.0
            cross_section = (c0 + c1*i + c2*i**2)*(i**-3)*10**-24

        elif [(i >= 2.471) & (i <3.210)]:
            c0, c1, c3 = 342.7, 18.7, 0
            cross_section = (c0 + c1*i + c2*i**2)*(i**-3)*10**-24

        elif [(i >= 3.210) & (i <4.038)]:
            c0, c1, c3 = 352.2, 18.7, 0
            cross_section = (c0 + c1*i + c2*i**2)*(i**-3)*10**-24

        elif [(i >= 4.038) & (i <7.111)]:
            c0, c1, c3 = 433.9, -2.4, 0.75
            cross_section = (c0 + c1*i + c2*i**2)*(i**-3)*10**-24

        elif [(i >= 7.111) & (i <8.331)]:
            c0, c1, c3 = 629.0, 30.9, 0.0
            cross_section = (c0 + c1*i + c2*i**2)*(i**-3)*10**-24

        elif [(i >= 8.331) & (i <10.0)]:
            c0, c1, c3 = 701.2, 25.2, 0.0
            cross_section = (c0 + c1*i + c2*i**2)*(i**-3)*10**-24

        elif [(i >= 10.0)]: 
            c0, c1, c3 = 701.2, 25.2, 0.0
            cross_section = (c0 + c1*i+ c2*i**2)*(i**-3)*10**-24
        return cross_section

Answer 1

Your return statement is in the for loop, so after the first energy, it will just return. What you probably want is to aggregate the individual cross_section values per energy and return a list or some collection of them. My example below is shortened but should give you the gist of it

EDIT: comments for clarity

Try:

def cross_section(energy): 
    cross_sections = []

    for i in energy: 

        if [(i >= .284) & (i <.400)]:
            c0, c1, c2 = 78.1, 18.8, 4.3
            cross_section = (c0 + c1*i + c2*i**2)*(i**-3)*10**-24
            print(i)
            print(cross_section)
        elif [(i >= .400) & (i <.532)]:
            c0, c1, c2 = 71.4, 66.8, -51.4
            cross_section = (c0 + c1*i + c2*i**2)*(i**-3)*10**-24

        # aggregate the individual cross_sections into a list   
        cross_sections.append(cross_section)

    # return the list after looping
    return cross_sections