import conanfile just once

conans/client/loader.py

@@ -33,12 +33,17 @@ def __init__(self, runner, output, python_requires):
         self._runner = runner
         self._output = output
         self._python_requires = python_requires
-        sys.modules["conans"].python_requires = self._python_requires
+        sys.modules["conans"].python_requires = python_requires
+        self.cached_conanfiles = {}
 
     def load_class(self, conanfile_path):
-        self._python_requires.valid = True
-        _, conanfile = parse_conanfile(conanfile_path, self._python_requires)
-        self._python_requires.valid = False
+        try:
+            return self.cached_conanfiles[conanfile_path]
+        except KeyError:
+            self._python_requires.valid = True
+            _, conanfile = parse_conanfile(conanfile_path, self._python_requires)
+            self._python_requires.valid = False
+            self.cached_conanfiles[conanfile_path] = conanfile
         return conanfile
 
     def load_export(self, conanfile_path, name, version, user, channel):

conans/test/optimize_conanfile_load_test.py

@@ -0,0 +1,36 @@
+import unittest
+
+from conans.test.utils.tools import TestClient
+
+
+class OptimizeConanFileLoadTest(unittest.TestCase):
+
+    def test_multiple_load(self):
+        """ when a conanfile is used more than once in a dependency graph, the python file
+        should be read and interpreted just once, then instance 2 different ConanFile
+        objects. The module global value "mycounter" is global to all instances, this
+        should be discouraged to use as if it was an instance value.
+        In this test there are 2 nodes "Build/0.1" as it is a build-requires of both the
+        conanfile.py and the test_package/conanfile.py
+        """
+        client = TestClient()
+        conanfile = """from conans import ConanFile
+mycounter = 0
+class Pkg(ConanFile):
+    mycounter2 = 0
+    def configure(self):
+        global mycounter
+        mycounter += 1
+        self.mycounter2 += 1
+        self.output.info("MyCounter1 %s, MyCounter2 %s" % (mycounter, self.mycounter2))
+"""
+        client.save({"conanfile.py": conanfile})
+
+        client.run("create . Build/0.1@user/testing")
+
+        client.save({"conanfile.py": conanfile,
+                     "test_package/conanfile.py": conanfile + "    def test(self): pass",
+                     "myprofile": "[build_requires]\nBuild/0.1@user/testing"})
+
+        client.run("create . Pkg/0.1@user/testing -pr=myprofile")
+        self.assertIn("Build/0.1@user/testing: MyCounter1 2, MyCounter2 1", client.out)

conans/test/unittests/model/transitive_reqs_test.py

@@ -115,6 +115,7 @@ def setUp(self):
                                         MockRequireResolver(), None, None)
 
     def root(self, content):
+        self.loader.cached_conanfiles = {}
         processed_profile = test_processed_profile()
         root_conan = self.retriever.root(content, processed_profile)
         deps_graph = self.builder.load_graph(root_conan, False, False, None,
@@ -430,7 +431,7 @@ class ChatConan(ConanFile):
         self.retriever.conan(bye_ref, bye_content2)
 
         with self.assertRaisesRegexp(ConanException, "Conflict in Bye/0.2@user/testing"):
-            _ = self.root(chat_content)
+            self.root(chat_content)
 
     def test_diamond_conflict_solved(self):
         chat_content = """

conans/test/unittests/model/version_ranges_test.py

@@ -182,6 +182,7 @@ class SayConan(ConanFile):
             self.retriever.conan(say_ref, say_content)
 
     def root(self, content, update=False):
+        self.loader.cached_conanfiles = {}
         processed_profile = test_processed_profile()
         root_conan = self.retriever.root(content, processed_profile)
         deps_graph = self.builder.load_graph(root_conan, update, update, None, processed_profile)