Raise exception if Python can't be found

On Windows run unexisting command `python` will get a different error
other then the normal `FileNotFoundError`.

__init__.py

@@ -2,7 +2,7 @@
 
 from calibre.customize import InterfaceActionBase
 
-VERSION = (3, 29, 2)
+VERSION = (3, 29, 3)
 
 
 class WordDumbDumb(InterfaceActionBase):

data/deps.json

@@ -3,6 +3,6 @@
   "lxml": "4.9.2",
   "thinc-apple-ops": "0.1.3",
   "torch": "2.0.1",
-  "rapidfuzz": "3.0.0",
+  "rapidfuzz": "3.1.1",
   "spacy_model": "3.5.0"
 }

deps.py

@@ -71,12 +71,18 @@ def install_deps(pkg: str, notif: Any) -> None:
 
 
 def which_python() -> tuple[str, str]:
+    """
+    Return Python command or file path and version string
+    """
     py = "python3"
     if iswindows:
         py = "py" if shutil.which("py") else "python"
     elif ismacos:
         py = homebrew_mac_bin_path("python3")
 
+    if shutil.which(py) is None:
+        raise Exception("PythonNotFound")
+
     if isfrozen:
         r = run_subprocess(
             [

error_dialogs.py

@@ -21,11 +21,11 @@ def error_dialog(title: str, message: str, error: str, parent: Any) -> None:
 
 def job_failed(job: Any, parent: Any = None) -> bool:
     if job and job.failed:
-        if "FileNotFoundError" in job.details and "subprocess.py" in job.details:
+        if "PythonNotFound" in job.details:
             error_dialog(
                 "We want... a shrubbery!",
                 _(
-                    "Please read the friendly <a href='{}'>manual</a> of how to install Python."
+                    "Can't find Python. Please read the <a href='{}'>document</a> of how to install Python."
                 ).format(INSTALL_PYTHON_DOC),
                 job.details,
                 parent,
@@ -34,7 +34,7 @@ def job_failed(job: Any, parent: Any = None) -> bool:
             error_dialog(
                 "Outdated Python",
                 _(
-                    "Please read the friendly <a href='{}'>manual</a> of how to install Python."
+                    "Your Python version is too old, please update to a newer version and read the <a href='{}'>document</a> for more information."
                 ).format(INSTALL_PYTHON_DOC),
                 job.details,
                 parent,