add backport_pr to tools

This is the script that has been used to back port pull requests to 0.13.1 so far.

tools/backport_pr.py

@@ -0,0 +1,89 b''
+"""
+Backport pull requests to a particular branch.
+
+Usage: backport_pr.py branch PR
+
+e.g.:
+
+    backport_pr.py 0.13.1 123
+
+to backport PR #123 onto branch 0.13.1
+
+"""
+
+from __future__ import print_function
+
+import os
+import sys
+from subprocess import Popen, PIPE, check_call, check_output
+from urllib import urlopen
+
+from gh_api import get_pull_request
+
+def find_rejects(root='.'):
+    for dirname, dirs, files in os.walk(root):
+        for fname in files:
+            if fname.endswith('.rej'):
+                yield os.path.join(dirname, fname)
+
+def get_current_branch():
+    branches = check_output(['git', 'branch'])
+    for branch in branches.splitlines():
+        if branch.startswith('*'):
+            return branch[1:].strip()
+
+def backport_pr(branch, num, project='ipython/ipython'):
+    current_branch = get_current_branch()
+    if branch != current_branch:
+        check_call(['git', 'checkout', branch])
+    pr = get_pull_request(project, num)
+    patch_url = pr['patch_url']
+    title = pr['title']
+    description = pr['body']
+    fname = "PR%i.patch" % num
+    if os.path.exists(fname):
+        print("using patch from {fname}".format(**locals()))
+        with open(fname) as f:
+            patch = f.read()
+    else:
+        req = urlopen(patch_url)
+        patch = req.read()
+    
+    msg = "Backport PR #%i: %s" % (num, title) + '\n\n' + description
+    check = Popen(['git', 'apply', '--check', '--verbose'], stdin=PIPE)
+    a,b = check.communicate(patch)
+    
+    if check.returncode:
+        print("patch did not apply, saving to {fname}".format(**locals()))
+        print("edit {fname} until `cat {fname} | git apply --check` succeeds".format(**locals()))
+        print("then run tools/backport_pr.py {num} again".format(**locals()))
+        if not os.path.exists(fname):
+            with open(fname, 'wb') as f:
+                f.write(patch)
+        return 1
+    
+    p = Popen(['git', 'apply'], stdin=PIPE)
+    a,b = p.communicate(patch)
+
+    commit = Popen(['git', 'commit', '-a', '-m', msg])
+    commit.communicate()
+    if commit.returncode:
+        print("commit failed!")
+        return 1
+    else:
+        print("PR #%i applied, with msg:" % num)
+        print()
+        print(msg)
+        print()
+    
+    if branch != current_branch:
+        check_call(['git', 'checkout', current_branch])
+    
+    return 0
+
+if __name__ == '__main__':
+    if len(sys.argv) < 3:
+        print(__doc__)
+        sys.exit(1)
+    
+    sys.exit(backport_pr(sys.argv[1], int(sys.argv[2])))