Precompute egg_prefix and versionless_egg_name.

Author: anntzer

importlib_metadata/__init__.py

@@ -495,6 +495,8 @@ class Prepared:
     normalized = None
     suffixes = 'dist-info', 'egg-info'
     exact_matches = [''][:0]
+    egg_prefix = ''
+    versionless_egg_name = ''
 
     def __init__(self, name):
         self.name = name
@@ -504,6 +506,9 @@ def __init__(self, name):
         self.exact_matches = [
             self.normalized + '.' + suffix for suffix in self.suffixes
         ]
+        legacy_normalized = self.legacy_normalize(self.name)
+        self.egg_prefix = legacy_normalized + '-'
+        self.versionless_egg_name = legacy_normalized + '.egg'
 
     @staticmethod
     def normalize(name):
@@ -536,12 +541,9 @@ def matches(self, cand, base):
         )
 
     def is_egg(self, base):
-        normalized = self.legacy_normalize(self.name or '')
-        prefix = normalized + '-' if normalized else ''
-        versionless_egg_name = normalized + '.egg' if self.name else ''
         return (
-            base == versionless_egg_name
-            or base.startswith(prefix)
+            base == self.versionless_egg_name
+            or base.startswith(self.egg_prefix)
             and base.endswith('.egg')
         )