Answer:
The Python code is given below with appropriate comments
Explanation:
#required method, assuming Volume class is defined and is accessible
def partyVolume(filename):
    #opening file in read mode, assuming file exists
    file=open(filename,'r')
    #reading initial volume
    initial=float(file.readline())
    #creating a Volume object with initial volume
    v=Volume(initial)
    #looping through rest of the lines in file
    for line in file.readlines():
        #removing trailing/leading white spaces/newlines and splitting line by white
        #space to get a list of tokens
        line=line.strip().split(' ')
        #ensuring that length of resultant list is 2
        if len(line)==2:
            #reading first value as direction (U or D)
            dir=line[0].upper()
            #reading second value as float value
            value=float(line[1])
            if dir=='U':
                #turning volume up
                v.up(value)
            elif dir=='D':
                #turning volume down
                v.down(value)
    #closing file, saving changes
    file.close()
    #returning volume
    return v