Corrected old "python3" syntax key to "python"; added UA header per dpaste TOS

IPython/core/magics/code.py

@@ -20,7 +20,7 b' import re'
 import sys
 import ast
 from itertools import chain
-from urllib.request import urlopen
+from urllib.request import Request, urlopen
 from urllib.parse import urlencode
 from pathlib import Path
 
@@ -29,6 +29,7 b' from IPython.core.error import TryNext, StdinNotImplementedError, UsageError'
 from IPython.core.macro import Macro
 from IPython.core.magic import Magics, magics_class, line_magic
 from IPython.core.oinspect import find_file, find_source_lines
+from IPython.core.release import version
 from IPython.testing.skipdoctest import skip_doctest
 from IPython.utils.contexts import preserve_keys
 from IPython.utils.path import get_py_filename
@@ -255,7 +256,7 b' class CodeMagics(Magics):'
 
         Options:
 
-          -d: Pass a custom description for the gist. The default will say
+          -d: Pass a custom description. The default will say
               "Pasted from IPython".
         """
         opts, args = self.parse_options(parameter_s, 'd:')
@@ -268,11 +269,13 b' class CodeMagics(Magics):'
 
         post_data = urlencode({
           "title": opts.get('d', "Pasted from IPython"),
-          "syntax": "python3",
+          "syntax": "python",
           "content": code
         }).encode('utf-8')
 
-        response = urlopen("http://dpaste.com/api/v2/", post_data)
+        request = Request("http://dpaste.com/api/v2/",
+            headers={"User-Agent": "IPython v{}".format(version)})
+        response = urlopen(request, post_data)
         return response.headers.get('Location')
 
     @line_magic