python Pymzml Cannot convert 'bytes' objecty to str implicityly

I am working on a code developed by others, and when I run following code:

os.chdir('C:\\Project Document\\BioPharm\\Mass Spectrometer\\Converted data')

f = open('List.txt','r')
filelist = f.readlines()
f.close()

all_spectra_mem = defaultdict(list)
all_spectra_interpol = defaultdict(list)
total_currents = defaultdict(list)

# Loop over files in filelist
for filename in filelist:
    filename = filename.strip()
    dataname = filename.split('.')[0]
    sys.stderr.write('= Processing file %s\n' %(filename))

    # Read the mzML file
    msrun = pymzml.run.Reader(filename)
    # print('This is msrun: ',msrun)
    # In memory copy of the spectra
    spectra_mem = []
    all_spectra_mem[dataname].append(spectra_mem)
    spectra_mem = all_spectra_mem[dataname]
    # List of ion currents
    ion_I = []

    # Loop over spectra
    n = 0
    x_ion = []
    for spe in msrun:
        n = n + 1
        # print('This is the indicator')
        #print(spe)
        #sys.exit('Error Message !')
        # Copy current spectrum to memory
        spectra_mem.append(copy.deepcopy(spe))
        # Get the ion current for normalization
        if 'total ion current' in spe:
            print('Yes')
            ion_I.append(spe['total ion current'])
            x_ion.append(n)
            # Event detection
        mad = robust.mad(ion_I)
        median = numpy.median(ion_I)
        mean = numpy.mean(ion_I)
        std = numpy.std(ion_I)
        events = defaultdict(list)
        current_event = 0
        n = -1
        last = 0
        for spe in spectra_mem:
            n = n + 1
            if 'total ion current' in spe:
                ion = spe['total ion current']
                if ion >= (median+10*mad):
                    if last < (median+10*mad):
                        current_event += 1
                    events[current_event].append([n,ion])
                last = ion
        sys.stderr.write(' # A total of %i events were detected:\n' %(len(events)))
        n = - 1

        for key in events:
            event = events[key]
            sp_list = []
            for sp in event:
                sp_list.append(sp[0])
            n = n + 1
            sys.stderr.write('\tEvent %i with spectra: %s\n' %(key,', '.join(str(x) for x in sp_list)))

    # Loop over events to get the peak
        global_peaks_x = []
        global_peaks_y = []
        for key in events:
            strfil='%s_event_%i.mzML' %(dataname,key)
            print('This is strfil: ', strfil)
            print('This is type indicator: ', type(strfil))
            #isinstance(strfil,str)
        # Write representative spectrum to new file
            run2 = pymzml.run.Writer(filename=str(strfil), run=msrun, overwrite=True)
            new_spectra = []
            event = events[key]
            event_currents = []
            best_I = 0
            best_sp = -1
            for ev in event:
                e1 = ev[0]
                I = ev[1]
                if I > best_I:
                    best_I = I
                    best_sp = e1
            global_peaks_x.append(best_sp)
            global_peaks_y.append(best_I)
            sys.stderr.write('\tProcessing event %s spectrum %i\n' %(key,best_sp))`enter code here`
            e1 = best_sp
            I = best_I
            run2.addSpec(spectra_mem[e1])
            run2.save()

I get this error

Traceback (most recent call last):

    File "C:\Project Document\Biopharm\Mass Spectrometer\Converted data|REIMES_event_identification.py", line 99, in <module>
    run2=pymzml.run.writer(filename=str(strfil), run=msrun, overwrite=True)
    File "C:\Anaconda3\lib\pymzml\run.py",line 708, in_init_input_xml_xtring +=new+line
    TypeError: Cannot convert 'Bytes' object to str implicitly
    Press any key to continue...

Appreciate that if you would suggest how to correct this issue.