Pfthb

I have an XML file where I need to add the tag 'document' after the tag which is the 3rd line in the file. So I need to be adding the 'document' tag in the 4th line of the file.
So far, the code that I have written to do so is as follows-

# search for element within xml file using regex-
file = open("path_to_file/5.xml", "r")
while True:
 line = file.readline()
 match = re.search(r'<!DOCTYPE .+', line)
 if match:
 print("Pattern found: ", match.group())
 print("Current file pos: ", file.tell())
 break


# Pattern found: <!DOCTYPE article SYSTEM "../article.dtd">
# Current file pos: 199

file.close()


# open xml file in append mode and write element/tag to file-
file = open("path_to_file/Desktop/5.xml", "a")

file.seek(199)
# 199

file.tell()
# 199

# write element/tag to xml file-
file.write('nnn<document>nnn')

# close file-
file.close()

But this is not doing the appropriate changes to the file as I am expecting it to. What's going wrong?

Thanks!

With most file writing APIs, including Python’s, you cannot insert data into the middle of a file (trying to do this overwrites data instead). You must read the entire file, process it, and write the entire file.

The “append” mode is only for adding data to the end of a file.

So your code becomes:

file = open("path_to_file/5.xml", "r")
lines = file.readlines()
file.close()

file = open("/home/arjun/Desktop/5.xml", "a")
for line in lines:
 match = re.search(r'<!DOCTYPE .+', line)
 if match:
 file.write('nnn<document>nnn')
 print("Pattern found: ", match.group())
 print("Current file pos: ", file.tell())
 else:
 file.write(line)
file.close()