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I work with YML files that include SIDs and the following structure:

 title:
 "2": "content a" # key: comment 
 "3": "content b" # key: comment 
 "4": "content c" # key: comment 
 "5": "content d" # key: comment 
 "6": "content e" # key: comment 

Usually, I have to remove some strings (note I never remove the number 1 or 2) so my new file looks like this:

 title:
 "2": "content a" # key: comment 
 "3": "content b" # key: comment 
 "5": "content d" # key: comment 
 "6": "content e" # key: comment

I need to rearrange the SIDs in order to have a sequence without any gap (in this case 2, 3, 4, 5, 6) independently on the content. For that reason I have written the following script. It works properly but I need to bring it into production so I need your help to reduce its complexity, make it clear and simpler or any advice you may have for a beginner (in both, Python and Stack Exchange).

import re, os

file=input ('YML file name: ')

#read the file and store its content as a list
os.chdir('/home/balaclava/Desktop/Scripts/YML fixer/')
rdfile= open(file)
cont=rdfile.readlines()
rdfile.close()

#list to store the reviewed strings
newfile=[]
newfile.append(cont[0]+cont[1])

#Get the second string SID as reference
numRegex = re.compile(r'd+')
act=numRegex.search(cont[1])
global refnum
refnum=int(act.group())

#Loop for each string (-2 due to the two first string are excluded)
for i in range(len(cont)-2): 
 act=numRegex.search(str(cont[i+2])) 
 temp=int(act.group()) 
#If the SID is correct, add item to newlist, else, fix it and add the item to the list. 
 if temp == (refnum+1): 
 newfile.append(cont[i+2])
 else:
 temp= (refnum+1) 
 change=numRegex.sub(str(temp), cont[i+2])
 newfile.append(change) 
 refnum += 1

#overwrite the file with the newlist content
with open (file,'w') as finalfile:
 finalfile.write(''.join(newfile))
 finalfile.close()