Use context managers to open files

Inspired by d50a6ddc1b.

docs/graphics-protocol.rst

@@ -107,7 +107,8 @@ features of the graphics protocol:
          sys.stdout.flush()
          cmd.clear()
 
-   write_chunked({'a': 'T', 'f': 100}, open(sys.argv[-1], 'rb').read())
+   with open(sys.argv[-1], 'rb') as f:
+      write_chunked({'a': 'T', 'f': 100}, f.read())
 
 
 Save this script as :file:`png.py`, then you can use it to display any PNG

docs/installer.py

@@ -229,7 +229,8 @@ def script_launch():
 
 def update_intaller_wrapper():
     # To run: python3 -c "import runpy; runpy.run_path('installer.py', run_name='update_wrapper')" installer.sh
-    src = open(__file__, 'rb').read().decode('utf-8')
+    with open(__file__, 'rb') as f:
+        src = f.read().decode('utf-8')
     wrapper = sys.argv[-1]
     with open(wrapper, 'r+b') as f:
         raw = f.read().decode('utf-8')