您可以使用Bitbucket REST API来实现这个功能。下面是一个示例代码片段，用于从项目中搜索所有Git存储库中的字符串。

import requests

url = "https://{BITBUCKET_HOSTNAME}/rest/api/1.0/projects/{PROJECT_KEY}/repos"

response = requests.get(url)
repositories = response.json()["values"]

for repo in repositories:
    repo_name = repo["name"]
    url = f"https://{BITBUCKET_HOSTNAME}/rest/api/1.0/projects/{PROJECT_KEY}/repos/{repo_name}/browse/"
    params = {'search': 'YOUR_SEARCH_STRING'}
    response = requests.get(url, params=params)
    search_results = response.json()
    print(f"Search results for repository {repo_name}:")
    for result in search_results["values"]:
        print(result["path"]["toString"])

请注意替换您自己的Bitbucket主机名和项目键。此代码片段将循环浏览项目中的每个Git存储库，并对每个存储库执行搜索操作。它将打印每个存储库中包含匹配字符串的文件路径。