Allow checking for backports via milestone

tools/backport_pr.py

@@ -32,6 +32,7 b' from gh_api import ('
     get_pull_request,
     get_pull_request_files,
     is_pull_request,
+    get_milestone_id,
 )
 
 def find_rejects(root='.'):
@@ -107,18 +108,33 b' def already_backported(branch, since_tag=None):'
     lines = check_output(cmd).decode('utf8')
     return set(int(num) for num in backport_re.findall(lines))
 
-def should_backport(labels):
+def should_backport(labels=None, milestone=None):
     """return set of PRs marked for backport"""
+    if labels is None and milestone is None:
+        raise ValueError("Specify one of labels or milestone.")
+    elif labels is not None and milestone is not None:
+        raise ValueError("Specify only one of labels or milestone.")
+    if labels is not None:
     issues = get_issues_list("ipython/ipython",
             labels=labels,
             state='closed',
             auth=True,
     )
+    else:
+        milestone_id = get_milestone_id("ipython/ipython", milestone,
+                auth=True)
+        issues = get_issues_list("ipython/ipython",
+                milestone=milestone_id,
+                state='closed',
+                auth=True,
+        )
+
     should_backport = set()
     for issue in issues:
         if not is_pull_request(issue):
             continue
-        pr = get_pull_request("ipython/ipython", issue['number'], auth=True)
+        pr = get_pull_request("ipython/ipython", issue['number'],
+                auth=True)
         if not pr['merged']:
             print ("Marked PR closed without merge: %i" % pr['number'])
             continue

tools/gh_api.py

@@ -156,6 +156,23 b' def get_issues_list(project, auth=False, **params):'
     pages = get_paged_request(url, headers=headers, **params)
     return pages
 
+def get_milestones(project, auth=False, **params):
+    url = "https://api.github.com/repos/{project}/milestones".format(project=project)
+    if auth:
+        headers = make_auth_header()
+    else:
+        headers = None
+    pages = get_paged_request(url, headers=headers, **params)
+    return pages
+
+def get_milestone_id(project, milestone, auth=False, **params):
+    pages = get_milestones(project, auth=auth, **params)
+    for page in pages:
+        if page['title'] == milestone:
+            return page['number']
+    else:
+        raise ValueError("milestone %s not found" % milestone)
+
 def is_pull_request(issue):
     """Return True if the given issue is a pull request."""
     return bool(issue.get('pull_request', {}).get('html_url', None))