better CMakeToolchain blocks filter

conan/tools/cmake/toolchain/blocks.py

@@ -840,8 +840,23 @@ def __init__(self, conanfile, toolchain, items=None):
             for name, block in items:
                 self._blocks[name] = block(conanfile, toolchain)
 
-    def remove(self, name):
+    def keys(self):
+        return self._blocks.keys()
+
+    def items(self):
+        return self._blocks.items()
+
+    def remove(self, name, *args):
         del self._blocks[name]
+        for arg in args:
+            del self._blocks[arg]
+
+    def select(self, name, *args):
+        """
+        keep the blocks provided as arguments, remove the others
+        """
+        to_keep = [name] + list(args)
+        self._blocks = OrderedDict((k, v) for k, v in self._blocks.items() if k in to_keep)
 
     def __setitem__(self, name, block_type):
         # Create a new class inheriting Block with the elements of the provided one

conans/test/unittests/tools/cmake/test_cmaketoolchain.py

@@ -49,6 +49,40 @@ def test_remove(conanfile):
     toolchain.blocks.remove("generic_system")
     content = toolchain.content
     assert 'CMAKE_SYSTEM_NAME' not in content
+    assert "CMAKE_CXX_FLAGS_INIT" in content
+    assert "_CMAKE_IN_TRY_COMPILE" in content
+
+    # remove multiple
+    toolchain = CMakeToolchain(conanfile)
+    toolchain.blocks.remove("generic_system", "cmake_flags_init")
+    content = toolchain.content
+    assert 'CMAKE_SYSTEM_NAME' not in content
+    assert "CMAKE_CXX_FLAGS_INIT" not in content
+    assert "_CMAKE_IN_TRY_COMPILE" in content
+
+
+def test_filter(conanfile):
+    toolchain = CMakeToolchain(conanfile)
+    toolchain.blocks.select("generic_system")
+    content = toolchain.content
+    assert 'CMAKE_SYSTEM_NAME' in content
+    assert "CMAKE_CXX_FLAGS_INIT" not in content
+    assert "_CMAKE_IN_TRY_COMPILE" not in content
+
+    # remove multiple
+    toolchain = CMakeToolchain(conanfile)
+    toolchain.blocks.select("generic_system", "cmake_flags_init")
+    content = toolchain.content
+    assert 'CMAKE_SYSTEM_NAME' in content
+    assert "CMAKE_CXX_FLAGS_INIT" in content
+    assert "_CMAKE_IN_TRY_COMPILE" not in content
+
+
+def test_dict_keys(conanfile):
+    toolchain = CMakeToolchain(conanfile)
+    assert "generic_system" in toolchain.blocks.keys()
+    items = dict(toolchain.blocks.items())
+    assert "generic_system" in items
 
 
 def test_template_remove(conanfile):