diffoscope/comparators/pdf.py

@@ -45,7 +45,11 @@ class PdfFile(File):
     def compare_details(self, other, source=None):
         xs = []
 
-        if PyPDF2 is not None:
+        if PyPDF2 is None:
+            self._comments.append(
+                "Installing the 'PyPDF2' package may produce a better output."
+            )
+        else:
             difference = Difference.from_text(
                 self.dump_pypdf2_metadata(self),
                 self.dump_pypdf2_metadata(other),

diffoscope/exc.py

@@ -31,19 +31,18 @@ class RequiredToolNotFound(Exception):
     def __init__(self, command):
         self.command = get_tool_name(command)
 
-    def get_package(self):
-        return get_package_provider(self.command)
-
     def get_comment(self, infix=''):
         xs = [
             "'{}' not available in path.".format(self.command),
             infix,
         ]
 
-        x = self.get_package()
+        x = get_package_provider(self.command)
         if x:
             xs.append(
-                "Install the '{}' package to get a better output.".format(x)
+                "Installing the '{}' package may produce a better output.".format(
+                    x
+                )
             )
 
         return " ".join(x for x in xs if x)

pyproject.toml

 [tool.black]
 line-length = 79
-py36 = true
 skip-string-normalization = true
 include = '(diffoscope|tests)/.+\.pyi?$'
 exclude = "diffoscope/changes.py"