使用python将一个文件中的文本部分替换为另一个文件中的文本

Question

First a bit of background: yes, I am new to python, but I like to dabble and learn things.

The goal is this: I have an intranet website here at work and they have us on a static server with no server side scripting allowed, meaning no PHP. So as I add new pages, I must update every freakin page's menu with the new link. Fortunately, I have an application called ArcGIS installed on my computer and with it came an installation of python. So I was thinking it would be nice to just put together a script that would read a file called "menu.txt" and then search recursively in my directory (and subdirectories) for files with ".html" and replace all text between some comment tags, like <!--begin menu--> and <!--end menu--> , with the text in "menu.txt"

So I started looking and found this snippet of code:

with open('menu.txt', 'r') as f:
    # read entire file into file1
    # ASSUMING 'file1.txt' is relatively small...
    file1 = f.read()

with open('test.html', 'r') as f:
    # ASSUMING 'file2.txt' is relatively small...
    file2 = f.read()    # read file into file2

# index() will raise an error if not found...
f1_start = file1.index('<!--123-->')
f1_end = file1.index('<!--321-->', f1_start)     # look for '//end' after '//start'

f2_start = file2.index('<!--123-->')
f2_end = file2.index('<!--321-->', f2_start)

# replace file2 lines with proper file1 lines
file2[f2_start:f2_end] = file1[f1_start:f1_end]

with open('test.html', 'w') as f:
    f.write(file2)

and I've also seen many examples using re , replace and such, but nothing that seems to be related to what i need. Anyway, right now I'm just trying it on the one file in the same directory, but when I run this on either my linux machine or in a windows python shell I get:

Traceback (most recent call last):
  File "P:\webpages\filereplace.py", line 18, in <module>
    file2[f2_start:f2_end] = file1[f1_start:f1_end]
TypeError: 'str' object does not support item assignment

I thought the problem might've been the with open part, but I don't know.

In this case the contents of menu.txt are essentially a beginning comment tag <!--123--> , then all of the <div id=menu>blah blah blah</div> , then an end comment tag <!--321--> . In my html file, I use the same comment tags, and you get the picture...

Any suggestions?

Answer 1

You are trying to modify a string in-place. This is not possible in python, because strings are immutable.

To achieve what you want, you would need create a new string from the parts of existing two strings:

# replace file2 lines with proper file1 lines
new_f = file2[:f2_start] + file1[f1_start:f1_end] + file2[f2_end:]

After that, write the contents to the file like so:

with open('test.html', 'w') as f:
    f.write(new_f)

Also, note that variable names file1 and file2 are a bit misleading here, as these are not file-like objects, but strings.

Answer 2

Most of the time, when dealing with in-place editing of files, I turn to the fileinput module:

import os
import fileinput

if __name__ == '__main__':
    # Menu should not have any marker, just pure contents
    with open('menu.txt') as f:
        menu_contents = f.read()

    # Initialize a few items
    start_marker = '<!--123-->'
    end_marker   = '<!--321-->'
    file_list = ['index.html', 'foo.html']
    found_old_contents = False

    # Loop to replace text in place
    for line in fileinput.input(file_list, inplace=True):
        line = line.rstrip()

        if line == start_marker:
            found_old_contents = True
            print line
            print menu_contents
        elif line == end_marker:
            found_old_contents = False

        if not found_old_contents:
            print line

Discussion

The key here is in the function fileinput.input(file_list, inplace=True) , which takes a list of file names, iterates through them line-by-line, and writes back to the files whatever you print out.

You will need to come up with a list of files (eg file_list ) by means of os.walk() or some other methods.

I have tested my code against two .html files and confident that it works. I cannot guaranty the results, especially for nested directories. Good luck.