how to change pi hostname in python file

1    import os
2    def setHostname(newhostname):
3        with open('/etc/hosts', 'r') as file:
4        # read a list of lines into data
5        data = file.readlines()
6
7        # the host name is on the 6th line following the IP address
8        # so this replaces that line with the new hostname
9        data[5] = '127.0.1.1       ' + newhostname
10
11        # save the file temporarily because /etc/hosts is protected
12        with open('temp.txt', 'w') as file:
13            file.writelines( data )
14
15        # use sudo command to overwrite the protected file
16        os.system('sudo mv temp.txt /etc/hosts')
17
18        # repeat process with other file
19        with open('/etc/hostname', 'r') as file:
20            data = file.readlines()
21
22        data[0] = newhostname
23
24        with open('temp.txt', 'w') as file:
25            file.writelines( data )
26
27        os.system('sudo mv temp.txt /etc/hostname')
28
29    #Then call the def
30    setHostname('whatever')
31