要获取两个分支之间的差异，可以使用Bitbucket的REST API来实现。以下是一个使用Python的代码示例：

import requests

def get_diff_between_branches(repo_slug, base_branch, compare_branch):
    base_url = 'https://api.bitbucket.org/2.0/repositories'
    url = f'{base_url}/{repo_slug}/diff/{base_branch}..{compare_branch}'

    response = requests.get(url)
    if response.status_code == 200:
        diff = response.text
        return diff
    else:
        return None

# 用法示例
repo_slug = 'your-repo-slug'
base_branch = 'base-branch'
compare_branch = 'compare-branch'

diff = get_diff_between_branches(repo_slug, base_branch, compare_branch)
if diff:
    print(diff)
else:
    print('Failed to get the diff')

请确保将repo_slug替换为你的仓库的slug，base_branch替换为基准分支的名称，compare_branch替换为要比较的分支的名称。

这个代码例子中使用了Python的requests库来发送GET请求并获取API的响应。如果请求成功，将返回两个分支之间的差异。如果请求失败，将返回None。

注意：在使用这个代码示例之前，请确保你已经通过Bitbucket的API认证，并具有访问相关仓库的权限。