diff --git a/README.md b/README.md
index e039c56..4987754 100644
--- a/README.md
+++ b/README.md
@@ -16,7 +16,7 @@ python-terraform is a python module provide a wrapper of `terraform` command lin
     t = Terraform()
     return_code, stdout, stderr = t.<cmd_name>(*arguments, **options)
     
-####For any parameter
+####For any argument
 simply pass the string to arguments of the method, for example,
 
     terraform apply target_dir 
@@ -79,6 +79,12 @@ or
     from python_terraform import Terraform
     tf = Terraform()
     tf.apply('/home/test', no_color=IsFlagged, refresh=False, var={'a':'b', 'c':'d'})
+
+or
+
+    from python_terraform import Terraform
+    tf = Terraform(working_dir='/home/test', variables={'a':'b', 'c':'d'})
+    tf.apply(no_color=IsFlagged, refresh=False)
     
 #### 2. fmt command, diff=true
 In shell:
@@ -91,6 +97,12 @@ In python-terraform:
     from python_terraform import Terraform
     tf = terraform(working_dir='/home/test')
     tf.fmt(diff=True)
+    
+## default values
+for apply/plan/destroy command, assign with following default value to make 
+caller easier in python
+1. ```input=False```, in this case process won't hang because you missing a variable
+1. ```no_color=IsFlagged```, in this case, stdout of result is easier for parsing
 
 ## Implementation
 IMHO, how terraform design boolean options is confusing. 
@@ -99,7 +111,7 @@ they're all boolean value but with different option type.
 This make api caller don't have a general rule to follow but to do 
 a exhaustive method implementation which I don't prefer to.
 Therefore I end-up with using `IsFlagged` or `IsNotFlagged` as value of option 
-like `-no-color` and `True/False` value reserved for option like 
+like `-no-color` and `True/False` value reserved for option like `refresh=true`
 
 
 
diff --git a/python_terraform/__init__.py b/python_terraform/__init__.py
index 5f5395c..86bcb7d 100644
--- a/python_terraform/__init__.py
+++ b/python_terraform/__init__.py
@@ -16,10 +16,6 @@ class IsFlagged:
     pass
 
 
-class IsNotFlagged:
-    pass
-
-
 class Terraform(object):
     """
     Wrapper of terraform command line tool
@@ -34,13 +30,17 @@ class Terraform(object):
                  var_file=None,
                  terraform_bin_path=None):
         """
-        :param working_dir: the folder of the working folder, if not given, will be where python
+        :param working_dir: the folder of the working folder, if not given,
+                            will be current working folder
         :param targets: list of target
-        :param state: path of state file relative to working folder
-        :param variables: variables for apply/destroy/plan command
-        :param parallelism: parallelism for apply/destroy command
-        :param var_file: passed as value of -var-file option, could be string or list
-            list stands for multiple -var-file option
+                        as default value of apply/destroy/plan command
+        :param state: path of state file relative to working folder,
+                    as a default value of apply/destroy/plan command
+        :param variables: default variables for apply/destroy/plan command,
+                        will be override by variable passing by apply/destroy/plan method
+        :param parallelism: default parallelism value for apply/destroy command
+        :param var_file: passed as value of -var-file option,
+                could be string or list, list stands for multiple -var-file option
         :param terraform_bin_path: binary path of terraform
         """
         self.working_dir = working_dir
@@ -148,15 +148,12 @@ class Terraform(object):
                 cmds += ['-{k}'.format(k=k)]
                 continue
 
-            if v is IsNotFlagged:
+            if v is None:
                 continue
 
             if type(v) is bool:
                 v = 'true' if v else 'false'
 
-            if not v:
-                continue
-
             cmds += ['-{k}={v}'.format(k=k, v=v)]
 
         cmds += args