Support labels for PullRequests (#752)

PullRequests can also have labels attached to them, like Issues or
Milestones. Extend PullRequest to also export them if they are present,
as well as adding methods to add, remove and set labels.

github/PullRequest.py

@@ -17,6 +17,7 @@
 # Copyright 2018 Gilad Shefer <gshefer@redhat.com>                             #
 # Copyright 2018 Thibault Jamet <tjamet@users.noreply.github.com>              #
 # Copyright 2018 sfdye <tsfdye@gmail.com>                                      #
+# Copyright 2018 Steve Kowalik <steven@wedontsleep.org>                        #
 #                                                                              #
 # This file is part of PyGithub.                                               #
 # http://pygithub.readthedocs.io/                                              #
@@ -36,6 +37,7 @@
 #                                                                              #
 ################################################################################
 
+import urllib
 import github.GithubObject
 import github.PaginatedList
 
@@ -202,6 +204,14 @@ class PullRequest(github.GithubObject.CompletableGithubObject):
         self._completeIfNotSet(self._issue_url)
         return self._issue_url.value
 
+    @property
+    def labels(self):
+        """
+        :type: list of :class:`github.Label.Label`
+        """
+        self._completeIfNotSet(self._labels)
+        return self._labels.value
+
     @property
     def merge_commit_sha(self):
         """
@@ -607,6 +617,72 @@ class PullRequest(github.GithubObject.CompletableGithubObject):
             list_item='users'
         )
 
+    def get_labels(self):
+        """
+        :calls: `GET /repos/:owner/:repo/pulls/:number/labels <http://developer.github.com/v3/issues/labels>`_
+        :rtype: :class:`github.PaginatedList.PaginatedList` of :class:`github.Label.Label`
+        """
+        return github.PaginatedList.PaginatedList(
+            github.Label.Label,
+            self._requester,
+            self.url + "/labels",
+            None
+        )
+
+    def add_to_labels(self, *labels):
+        """
+        :calls: `POST /repos/:owner/:repo/pulls/:number/labels <http://developer.github.com/v3/issues/labels>`_
+        :param label: :class:`github.Label.Label` or string
+        :rtype: None
+        """
+        assert all(isinstance(element, (github.Label.Label, str, unicode)) for element in labels), labels
+        post_parameters = [label.name if isinstance(label, github.Label.Label) else label for label in labels]
+        headers, data = self._requester.requestJsonAndCheck(
+            "POST",
+            self.url + "/labels",
+            input=post_parameters
+        )
+
+    def delete_labels(self):
+        """
+        :calls: `DELETE /repos/:owner/:repo/pulls/:number/labels <http://developer.github.com/v3/issues/labels>`_
+        :rtype: None
+        """
+        headers, data = self._requester.requestJsonAndCheck(
+            "DELETE",
+            self.url + "/labels"
+        )
+
+    def remove_from_labels(self, label):
+        """
+        :calls: `DELETE /repos/:owner/:repo/pulls/:number/labels/:name <http://developer.github.com/v3/issues/labels>`_
+        :param label: :class:`github.Label.Label` or string
+        :rtype: None
+        """
+        assert isinstance(label, (github.Label.Label, str, unicode)), label
+        if isinstance(label, github.Label.Label):
+            label = label._identity
+        else:
+            label = urllib.quote(label)
+        headers, data = self._requester.requestJsonAndCheck(
+            "DELETE",
+            self.url + "/labels/" + label
+        )
+
+    def set_labels(self, *labels):
+        """
+        :calls: `PUT /repos/:owner/:repo/pulls/:number/labels <http://developer.github.com/v3/issues/labels>`_
+        :param label: :class:`github.Label.Label`
+        :rtype: None
+        """
+        assert all(isinstance(element, (github.Label.Label, str, unicode)) for element in labels), labels
+        post_parameters = [label.name if isinstance(label, github.Label.Label) else label for label in labels]
+        headers, data = self._requester.requestJsonAndCheck(
+            "PUT",
+            self.url + "/labels",
+            input=post_parameters
+        )
+
     def is_merged(self):
         """
         :calls: `GET /repos/:owner/:repo/pulls/:number/merge <http://developer.github.com/v3/pulls>`_
@@ -663,6 +739,7 @@ class PullRequest(github.GithubObject.CompletableGithubObject):
         self._html_url = github.GithubObject.NotSet
         self._id = github.GithubObject.NotSet
         self._issue_url = github.GithubObject.NotSet
+        self._labels = github.GithubObject.NotSet
         self._merge_commit_sha = github.GithubObject.NotSet
         self._mergeable = github.GithubObject.NotSet
         self._mergeable_state = github.GithubObject.NotSet
@@ -723,6 +800,8 @@ class PullRequest(github.GithubObject.CompletableGithubObject):
             self._id = self._makeIntAttribute(attributes["id"])
         if "issue_url" in attributes:  # pragma no branch
             self._issue_url = self._makeStringAttribute(attributes["issue_url"])
+        if "labels" in attributes:  # pragma no branch
+            self._labels = self._makeListOfClassesAttribute(github.Label.Label, attributes["labels"])
         if "merge_commit_sha" in attributes:  # pragma no branch
             self._merge_commit_sha = self._makeStringAttribute(attributes["merge_commit_sha"])
         if "mergeable" in attributes:  # pragma no branch