Error Parsing Data from Xml Python "Nameerror: Name 'Xxx' Is Not Defined"

Code: Parsing some data from an XML file as , taking user input and trying to replace a sub-string in the text parsed from the XML file. (This is for a upcoming HID attack framework , part of my offensive computer security degree)

def Generate_Payload(payload):
      print " Selection : " , payload
      import xml.etree.ElementTree as ET
      payload_raw = ET.parse(payload).getroot().find('payload').text                
      print payload_raw
      shell_name = input("Please enter the name of your malicious apk :")                   
      payload_raw_filtered = payload_raw.replace('#APKNAME#', shell_name)                   
      print payload_raw_filtered
      os.system('pause')

Error:

           Please enter the name of your malsivus apk :apk
            Traceback (most recent call last):
              File "C:\Users\Master\Documents\GitHub\HIDAAF\hidaaf.py", line 52, in <module>
                List_Payloads()
              File "C:\Users\Master\Documents\GitHub\HIDAAF\hidaaf.py", line 41, in List_Payloads
                Generate_Payload(filenames[payload - 1 ])
              File "C:\Users\Master\Documents\GitHub\HIDAAF\hidaaf.py", line 18, in Generate_Payload
                shell_name= input("Please enter the name of your malicious apk :")
              File "<string>", line 1, in <module>
            NameError: name 'apk' is not defined