escape callback parameter for java(okhttp) and python

modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/AbstractJavaCodegen.java

@@ -377,6 +377,11 @@ public abstract class AbstractJavaCodegen extends DefaultCodegen implements Code
 
     @Override
     public String toParamName(String name) {
+        // to avoid conflicts with 'callback' parameter for async call
+        if ("callback".equals(name)) {
+            return "paramCallback";
+        }
+
         // should be the same as variable name
         return toVarName(name);
     }

modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/PythonClientCodegen.java

@@ -349,6 +349,11 @@ public class PythonClientCodegen extends DefaultCodegen implements CodegenConfig
 
     @Override
     public String toParamName(String name) {
+        // to avoid conflicts with 'callback' parameter for async call
+        if ("callback".equals(name)) {
+            return "param_callback";
+        }
+
         // should be the same as variable name
         return toVarName(name);
     }