Make ipykernel work without debugpy

debugpy is an optional dependency because only frontends with
debugging support (Jupyter lab) can really use its features.

Fixes: #712

.github/workflows/ci.yml

@@ -110,3 +110,44 @@ jobs:
     - name: Check Docstrings
       run: |
         velin . --check --compact
+  test_without_debugpy:
+    runs-on: ${{ matrix.os }}-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu]
+        python-version: [ '3.9' ]
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v1
+    - name: Install Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v1
+      with:
+        python-version: ${{ matrix.python-version }}
+        architecture: 'x64'
+    - name: Upgrade packaging dependencies
+      run: |
+        pip install --upgrade pip setuptools wheel --user
+    - name: Get pip cache dir
+      id: pip-cache
+      run: |
+        echo "::set-output name=dir::$(pip cache dir)"
+    - name: Cache pip
+      uses: actions/cache@v1
+      with:
+        path: ${{ steps.pip-cache.outputs.dir }}
+        key: ${{ runner.os }}-pip-${{ matrix.python-version }}-${{ hashFiles('setup.py') }}
+        restore-keys: |
+          ${{ runner.os }}-pip-${{ matrix.python-version }}-
+          ${{ runner.os }}-pip-
+    - name: Install the Python dependencies without debugpy
+      run: |
+        pip install --pre --upgrade --upgrade-strategy=eager .[test]
+        pip uninstall --yes debugpy
+    - name: List installed packages
+      run: |
+        pip freeze
+    - name: Run the tests
+      timeout-minutes: 10
+      run: |
+        pytest ipykernel -vv -s --durations 10

ipykernel/ipkernel.py

@@ -17,7 +17,6 @@
 from .kernelbase import Kernel as KernelBase
 from .zmqshell import ZMQInteractiveShell
 from .eventloops import _use_appnope
-from .debugger import Debugger
 from .compiler import XCachingCompiler
 
 try:
@@ -34,6 +33,13 @@
 except ImportError:
     _use_experimental_60_completion = False
 
+try:
+    import debugpy
+    from .debugger import Debugger
+    _is_debugpy_available = True
+except ImportError:
+    _is_debugpy_available = False
+
 _EXPERIMENTAL_KEY_NAME = '_jupyter_types_experimental'
 
 
@@ -46,7 +52,7 @@ class IPythonKernel(KernelBase):
         help="Set this flag to False to deactivate the use of experimental IPython completion APIs.",
     ).tag(config=True)
 
-    debugpy_stream = Instance(ZMQStream, allow_none=True)
+    debugpy_stream = Instance(ZMQStream, allow_none=True) if _is_debugpy_available else None
 
     user_module = Any()
     @observe('user_module')
@@ -72,11 +78,12 @@ def __init__(self, **kwargs):
         super(IPythonKernel, self).__init__(**kwargs)
 
         # Initialize the Debugger
-        self.debugger = Debugger(self.log,
-                                 self.debugpy_stream,
-                                 self._publish_debug_event,
-                                 self.debug_shell_socket,
-                                 self.session)
+        if _is_debugpy_available:
+            self.debugger = Debugger(self.log,
+                                    self.debugpy_stream,
+                                    self._publish_debug_event,
+                                    self.debug_shell_socket,
+                                    self.session)
 
         # Initialize the InteractiveShell subclass
         self.shell = self.shell_class.instance(parent=self,
@@ -152,10 +159,11 @@ def __init__(self, **kwargs):
     }
 
     def dispatch_debugpy(self, msg):
-        # The first frame is the socket id, we can drop it
-        frame = msg[1].bytes.decode('utf-8')
-        self.log.debug("Debugpy received: %s", frame)
-        self.debugger.tcp_client.receive_dap_frame(frame)
+        if _is_debugpy_available:
+            # The first frame is the socket id, we can drop it
+            frame = msg[1].bytes.decode('utf-8')
+            self.log.debug("Debugpy received: %s", frame)
+            self.debugger.tcp_client.receive_dap_frame(frame)
 
     @property
     def banner(self):
@@ -414,7 +422,8 @@ def do_complete(self, code, cursor_pos):
                 'status' : 'ok'}
 
     async def do_debug_request(self, msg):
-        return await self.debugger.process_request(msg)
+        if _is_debugpy_available:
+            return await self.debugger.process_request(msg)
 
     def _experimental_do_complete(self, code, cursor_pos):
         """

ipykernel/kernelspec.py

@@ -13,6 +13,8 @@
 
 from jupyter_client.kernelspec import KernelSpecManager
 
+from .ipkernel import _is_debugpy_available
+
 pjoin = os.path.join
 
 KERNEL_NAME = 'python%i' % sys.version_info[0]
@@ -52,7 +54,7 @@ def get_kernel_dict(extra_arguments=None):
         'argv': make_ipkernel_cmd(extra_arguments=extra_arguments),
         'display_name': 'Python %i (ipykernel)' % sys.version_info[0],
         'language': 'python',
-        'metadata': { 'debugger': True}
+        'metadata': { 'debugger': _is_debugpy_available}
     }