[Doitsu]

Originally Posted by Capricorn

What tools and websites are good to learn python?

I'd strongly recommend Automate the Boring Stuff with Python by Al Sweigart, which is available for free online.
You'll also need to download the Sigil Framework Guide.
You also might find the Sigil test plugin helpful because it demonstrates most Sigil-specific Python functions.

Here's a minimal proof-of-concept edit plugin that will wrap "the" in all html files in <b> tags:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import sys, os

# main routine    
def run(bk):
    # iterate over all html files
    for html_id, href in bk.text_iter():
        # read orignal html code from file
        original_html = bk.readfile(html_id)
        # modify html code
        modified_html = original_html.replace('the', '<b>the</b>') 
        if modified_html != original_html:
            # write modified html code to file
            bk.writefile(html_id, modified_html)
            print(os.path.basename(href) + ' updated')
    return 0

def main():
    print('I reached main when I should not have\n')
    return -1

if __name__ == "__main__":
    sys.exit(main())

As you can see it doesn't really require much code. BTW, Sigil comes with a fork of the BeautifulSoup library that makes it really easy to manipulate HTML content. To import it you must use:

from sigil_bs4 import BeautifulSoup