Dateien Umbenennen mit Python

# imports 
import os
import datetime
import re
# create todays date
today = datetime.date.today().strftime("%Y-%m-%d")  
# source dir
sourceDir = "/path/to/folder"  
# extension of files
strExtension = ".pdf"  
# for each file in source directory
for file in os.listdir(sourceDir):
    # if file ends with extension
    if file.endswith(strExtension):
        # variable for new name
        strNewName = ""  
        # check for strings in filename and create new name accordingly
        if "ReA" in file:  
            strNewName = today + "_Amazon_" + file  
        elif "Telekom" in file:  
            strNewName = today + "_Telekom_" + file  
        elif "Str_" in file:  
            strNewName = today + "_RG_Hausstrom_" + file  

        # if filename should be changed
        if strNewName != "":  
            # append number with with format _[0-9]* to the end of the basename if file already exists
            cnt = 1
            while os.path.isfile(os.path.join(sourceDir,strNewName)):
                strNewName = re.sub('_\d+$','',os.path.splitext(strNewName),1) + "_" + str(cnt) + os.path.splitext(filePath)[1]  
                cnt += 1
            # sourcepath
            sourcePath = os.path.join(sourceDir,file)
            # destination path
            destPath = os.path.join(sourceDir,strNewName)
            # actually rename the file
            os.rename(sourcePath,destPath)

strNewName = today + "_Amazon_" + file.split("_",1)[1]