Replace paths easily in qBittorrent .fastresume (useful when switching from windows to linux)

qbit-fastresume-path-changer.py

import os
import re

# Insert the path where you keep your fast resume files here.
# Make a backup first!!!

torrentsDir = r'/torrents/'

# Insert paths to be replaced here. Dictionary key is current path. Dictionary value is new path
# If left empty, the script will only detect paths

fastresumePaths = {}

    
if not fastresumePaths:
    print('Finding paths...\n')
    detectedPaths = []

# Loop through torrents directory
for file in os.listdir(torrentsDir):
    if file.endswith('.fastresume'):
        with open(torrentsDir + file, 'rb') as fastresumeFile:
            filedata = fastresumeFile.read()
           
        query = re.search(b'save_path(\d+):', filedata)
        
        if query is None:
            print(f'Could not find path in {file}')
        else:
            pathLen = int(query.group(1))
            path = filedata[query.end():query.end() + pathLen]
            
            # check if user entered paths to change or not
            if fastresumePaths:
                if path in fastresumePaths:
                    newPath = fastresumePaths[path]
                    filedata = filedata.replace(
                        bytes(str(pathLen), 'utf-8') + b':' + path,
                        bytes(str(len(newPath)), 'utf-8') + b':' + newPath
                    )
                    print(f"Replaced {path} with {newPath}")
                
                    with open(torrentsDir + file, 'wb') as fastresumeFile:
                        fastresumeFile.write(filedata)
            else:
                if path not in detectedPaths:
                    detectedPaths.append(path)

if fastresumePaths is None or not fastresumePaths:    
    if not detectedPaths:
        print('No paths were found')
    else:
        print('The following paths were found\n')
        
        for path in detectedPaths:
            print(path)

        print('\nCopy the following code into the "fastresumePaths" variable to replace paths.\n')
        
        maxPathLength = len(max(detectedPaths, key=len)) + 4
        
        print(f"#   {'Original Path'.ljust(maxPathLength)}  New Path")
        print(f"#  {'-'*(maxPathLength)}  {'-'*(maxPathLength)}\n")
        print('fastresumePaths = {')
        
        for path in detectedPaths:
            print(f"    {str(path).ljust(maxPathLength)}: {str(path).ljust(maxPathLength)},")

        print('}\n')

Also very useful when qbittorrent decides to ignore that I moved the torrent! Thanks for your tool!

A little note: in my experience both the keys and the values of the fastresumePaths dict need to be a "byte literal", like this: b"D:\\my\\path".
This is crucial when your path contains non-english characters (you can get a copy of the value you need when running the script with a debugger in PyCharm, but probably print()ing it could also work), but also python complained when the dict value was not a byte literal, because it didnt know how to concat it.. just put the b before the string and now qbittorrent finally finds the torrents where they actually are.

I just want to mention that, there is another project called qbt_migrate which is also available through PyPI.