Make psutil optional at runtime

ipykernel/kernelbase.py

@@ -36,7 +36,6 @@
     # jupyter_client < 5, use local now()
     now = datetime.now
 
-import psutil
 import zmq
 from IPython.core.error import StdinNotImplementedError
 from jupyter_client.session import Session
@@ -62,6 +61,19 @@
 from .iostream import OutStream
 from .utils import LazyDict, _async_in_context
 
+psutil: t.Any | None
+try:
+    import psutil as _psutil
+except ImportError:
+    psutil = None
+else:
+    psutil = _psutil
+
+if psutil is None:
+    _NO_SUCH_PROCESS: tuple[type[BaseException], ...] = ()
+else:
+    _NO_SUCH_PROCESS = (psutil.NoSuchProcess,)
+
 _AWAITABLE_MESSAGE: str = (
     "For consistency across implementations, it is recommended that `{func_name}`"
     " either be a coroutine function (`async def`) or return an awaitable object"
@@ -97,7 +109,7 @@ class Kernel(SingletonConfigurable):
     # attribute to override with a GUI
     eventloop = Any(None)
 
-    processes: dict[str, psutil.Process] = {}
+    processes: dict[int, t.Any] = {}
 
     @observe("eventloop")
     def _update_eventloop(self, change):
@@ -1172,13 +1184,18 @@ async def usage_request(self, stream, ident, parent):
         if not self.session:
             return
         reply_content = {"hostname": socket.gethostname(), "pid": os.getpid()}
+        if psutil is None:
+            reply_content["cpu_count"] = os.cpu_count()
+            reply_msg = self.session.send(stream, "usage_reply", reply_content, parent, ident)
+            self.log.debug("%s", reply_msg)
+            return
+
         current_process = psutil.Process()
         all_processes = [current_process, *current_process.children(recursive=True)]
         # Ensure 1) self.processes is updated to only current subprocesses
         # and 2) we reuse processes when possible (needed for accurate CPU)
         self.processes = {
-            process.pid: self.processes.get(process.pid, process)  # type:ignore[misc,call-overload]
-            for process in all_processes
+            process.pid: self.processes.get(process.pid, process) for process in all_processes
         }
         reply_content["kernel_cpu"] = sum(
             [
@@ -1196,7 +1213,7 @@ async def usage_request(self, stream, ident, parent):
         cpu_percent = psutil.cpu_percent()
         # https://psutil.readthedocs.io/en/latest/index.html?highlight=cpu#psutil.cpu_percent
         # The first time cpu_percent is called it will return a meaningless 0.0 value which you are supposed to ignore.
-        if cpu_percent is not None and cpu_percent != 0.0:  # type:ignore[redundant-expr]
+        if cpu_percent is not None and cpu_percent != 0.0:
             reply_content["host_cpu_percent"] = cpu_percent
         reply_content["cpu_count"] = psutil.cpu_count(logical=True)
         reply_content["host_virtual_memory"] = dict(psutil.virtual_memory()._asdict())
@@ -1476,7 +1493,7 @@ def _signal_children(self, signum):
                     p.kill()
                 else:
                     p.send_signal(signum)
-            except psutil.NoSuchProcess:
+            except _NO_SUCH_PROCESS:
                 pass
 
     def _process_children(self):
@@ -1486,6 +1503,9 @@ def _process_children(self):
         - including parents and self with killpg
         - including all children that may have forked-off a new group
         """
+        if psutil is None:
+            return []
+
         kernel_process = psutil.Process()
         all_children = kernel_process.children(recursive=True)
         if os.name == "nt":

pyproject.toml

@@ -31,7 +31,6 @@ dependencies = [
     "matplotlib-inline>=0.1",
     'appnope>=0.1.2;platform_system=="Darwin"',
     "pyzmq>=25",
-    "psutil>=5.7",
     "packaging>=22",
 ]
 
@@ -59,6 +58,7 @@ test = [
     "flaky",
     "ipyparallel",
     "pre-commit",
+    "psutil>=5.7",
     "pytest-asyncio>=0.23.5",
     "pytest-timeout"
 ]

tests/test_kernel_direct.py

@@ -4,6 +4,7 @@
 # Distributed under the terms of the Modified BSD License.
 
 import os
+import signal
 import warnings
 
 import pytest
@@ -152,6 +153,32 @@ async def test_connect_request(kernel):
     await kernel.connect_request(kernel.shell_stream, "foo", {})
 
 
+async def test_usage_request_without_psutil(kernel, monkeypatch):
+    import ipykernel.kernelbase as kernelbase
+
+    monkeypatch.setattr(kernelbase, "psutil", None)
+    reply = await kernel.test_control_message("usage_request", {})
+    content = reply["content"]
+
+    assert reply["header"]["msg_type"] == "usage_reply"
+    assert content["hostname"]
+    assert content["pid"] == os.getpid()
+    assert content["cpu_count"] == os.cpu_count()
+    assert "host_cpu_percent" not in content
+    assert "host_virtual_memory" not in content
+    assert "kernel_memory" not in content
+
+
+async def test_child_process_fallbacks_without_psutil(kernel, monkeypatch):
+    import ipykernel.kernelbase as kernelbase
+
+    monkeypatch.setattr(kernelbase, "psutil", None)
+
+    assert kernel._process_children() == []
+    kernel._signal_children(signal.SIGTERM)
+    await kernel._progressively_terminate_all_children()
+
+
 async def test_send_interrupt_children(kernel):
     kernel._send_interrupt_children()