如果你使用GitLab，你可以使用requests库。例如：

import requests

# API endpoint and access token
gitlab_url = 'https://gitlab.example.com/api/v4'
access_token = '<your-access-token>'

# MR ID and project ID
mr_id = 123
project_id = 456

# get MR info
response = requests.get(f'{gitlab_url}/projects/{project_id}/merge_requests/{mr_id}', headers={'Private-Token': access_token})

# Extract target branch
target_branch = response.json()['target_branch']

print(f'The target branch for MR {mr_id} is {target_branch}')

如果你使用GitHub，你可以使用github库。示例：

from github import Github

# token and repository info
access_token = '<your-access-token>'
repo_name = '<owner>/<repo>'
pr_id = 123

g = Github(access_token)

# repository object
repo = g.get_repo(repo_name)

# pull request object
pr = repo.get_pull(pr_id)

# target branch name
target_branch = pr.base.ref

print(f'The target branch for PR {pr_id} is {target_branch}')