从文件python中删除字符串和字符串之前的所有行

Question

I have a filename with thousands of lines of data in it. I am reading in the filename and editing it.

The following tag is about ~900 lines in or more (it varies per file):

<Report name="test" xmlns:cm="http://www.domain.org/cm">

I need to remove that line and everything before it in several files. so I need to the code to search for that tag and delete it and everything above it it will not always be 900 lines down, it will vary; however, the tag will always be the same.

I already have the code to read in the lines and write to a file. I just need the logic behind finding that line and removing it and everything before it.

I tried reading the file in line by line and then writing to a new file once it hits on that string, but the logic is incorrect:

readFile = open(firstFile)
lines = readFile.readlines()
readFile.close()
w = open('test','w')
for item in lines:
    if (item == "<Report name="test" xmlns:cm="http://www.domain.org/cm">"):
        w.writelines(item)
w.close()

In addition, the exact string will not be the same in each file. The value "test" will be different. I perhaps need to check for the tag name ""

Any help will be much appreciated.

Answer 1

You can use a flag like tag_found to check when lines should be written to the output. You initially set the flag to False , and then change it to True once you've found the right tag. When the flag is True , you copy the line to the output file.

TAG = '<Report name="test" xmlns:cm="http://www.domain.org/cm">'

tag_found = False
with open('tag_input.txt') as in_file:
    with open('tag_output.txt', 'w') as out_file:
        for line in in_file:
            if not tag_found:
                if line.strip() == TAG:
                    tag_found = True
            else:
                out_file.write(line)

PS: The with open(filename) as in_file: syntax is using what Python calls a "context manager"- see here for an overview. The short explanation of them is that they automatically take care of closing the file safely for you when the with: block is finished, so you don't have to remember to put in my_file.close() statements.

Answer 2

You can use a regular expression to match you line:

regex1 = '^<Report name=.*xmlns:cm="http://www.domain.org/cm">$'

Get the index of the item that matches the regex:

listIndex = [i for i, item in enumerate(lines) if re.search(regex, item)]

Slice the list:

listLines = lines[listIndex:]

And write to a file:

with open("filename.txt", "w") as fileOutput:
    fileOutput.write("\n".join(listLines))

pseudocode

Try something like this:

import re

regex1 = '^<Report name=.*xmlns:cm="http://www.domain.org/cm">$' # Variable @name
regex2 = '^<Report name=.*xmlns:cm=.*>$' # Variable @name & @xmlns:cm

with open(firstFile, "r") as fileInput:
    listLines = fileInput.readlines()

listIndex = [i for i, item in enumerate(listLines) if re.search(regex1, item)]
# listIndex = [i for i, item in enumerate(listLines) if re.search(regex2, item)] # Uncomment for variable @name & @xmlns:cm

with open("out_" + firstFile, "w") as fileOutput:
    fileOutput.write("\n".join(lines[listIndex:]))