move Margin to its own module

babi/main.py

@@ -31,6 +31,7 @@ from typing import Union
 
 from babi.list_spy import ListSpy
 from babi.list_spy import MutableSequenceNoSlice
+from babi.margin import Margin
 
 VERSION_STR = 'babi v0'
 TCallable = TypeVar('TCallable', bound=Callable[..., Any])
@@ -101,31 +102,6 @@ class Key(NamedTuple):
     keyname: bytes
 
 
-class Margin(NamedTuple):
-    header: bool
-    footer: bool
-
-    @property
-    def body_lines(self) -> int:
-        return curses.LINES - self.header - self.footer
-
-    @property
-    def page_size(self) -> int:
-        if self.body_lines <= 2:
-            return 1
-        else:
-            return self.body_lines - 2
-
-    @classmethod
-    def from_current_screen(cls) -> 'Margin':
-        if curses.LINES == 1:
-            return cls(header=False, footer=False)
-        elif curses.LINES == 2:
-            return cls(header=False, footer=True)
-        else:
-            return cls(header=True, footer=True)
-
-
 class Status:
     def __init__(self) -> None:
         self._status = ''

babi/margin.py

@@ -0,0 +1,27 @@
+import curses
+from typing import NamedTuple
+
+
+class Margin(NamedTuple):
+    header: bool
+    footer: bool
+
+    @property
+    def body_lines(self) -> int:
+        return curses.LINES - self.header - self.footer
+
+    @property
+    def page_size(self) -> int:
+        if self.body_lines <= 2:
+            return 1
+        else:
+            return self.body_lines - 2
+
+    @classmethod
+    def from_current_screen(cls) -> 'Margin':
+        if curses.LINES == 1:
+            return cls(header=False, footer=False)
+        elif curses.LINES == 2:
+            return cls(header=False, footer=True)
+        else:
+            return cls(header=True, footer=True)