some commit

Difficult_Rocket/api/__init__.py

@@ -11,11 +11,11 @@ github: @shenjackyuanjie
 gitee:  @shenjackyuanjie
 """
 
-from .Exp import TexturesError, LanguageError
-from .delivery import Delivery
-from .new_thread import new_thread
 from .tools import config
 from .translate import Lang
+from .delivery import Delivery
+from .new_thread import new_thread
+from .Exp import TexturesError, LanguageError
 
 __all__ = ['TexturesError',
            'LanguageError',
@@ -23,3 +23,4 @@ __all__ = ['TexturesError',
            'Delivery',
            'config',
            'Lang']
+

Difficult_Rocket/api/calculation.py

@@ -17,7 +17,7 @@ import decimal
 from typing import List, Optional
 from decimal import Decimal
 
-from Difficult_Rocket.api
+
 
 # linear_algebra
 

Difficult_Rocket/api/scientific_unit.py

@@ -11,18 +11,31 @@ github: @shenjackyuanjie
 gitee:  @shenjackyuanjie
 """
 
-__all__ = ['Newton',
-           'Metre',
-           'Second']
+
+class Units:
+    """
+    base class of all units
+    """
+    def __init__(self):
+        pass
 
 
-class Newton:
+class _Newton(Units):
     pass
 
 
-class Metre:
+newton = _Newton()
+
+
+class _Metre(Units):
     pass
 
 
-class Second:
+metre = _Metre()
+
+
+class _Second(Units):
     pass
+
+
+second = _Second()