fix issue #79: do monitor detection in MSS constructor

CONTRIBUTORS

@@ -9,6 +9,9 @@
 Alexander 'thehesiod' Mohr [https://github.com/thehesiod]
     - Windows: robustness to MSS.get_pixels()
 
+Andreas Buhr [https://www.andreasbuhr.de]
+    - Bugfix for multi-monitor detection
+
 bubulle [http://indexerror.net/user/bubulle]
     - Windows: efficiency of MSS.get_pixels()
 

mss/base.py

@@ -16,7 +16,6 @@ class MSSBase(object):
 
     cls_image = ScreenShot  # type: object
     compression_level = 6  # type: int
-    _monitors = []  # type: List[Dict[str, int]]
 
     def __enter__(self):
         # type: () -> MSSBase

mss/darwin.py

@@ -67,6 +67,8 @@ def __init__(self):
         # type: () -> None
         """ macOS initialisations. """
 
+        self._monitors = []  # type: List[Dict[str, int]]
+
         coregraphics = ctypes.util.find_library("CoreGraphics")
         if not coregraphics:
             raise ScreenShotError("No CoreGraphics library found.")

mss/linux.py

@@ -160,6 +160,8 @@ def __init__(self, display=None):
         # type: (bytes) -> None
         """ GNU/Linux initialisations. """
 
+        self._monitors = []  # type: List[Dict[str, int]]
+
         if not display:
             try:
                 display = os.environ["DISPLAY"].encode("utf-8")

mss/windows.py

@@ -62,6 +62,8 @@ def __init__(self):
         # type: () -> None
         """ Windows initialisations. """
 
+        self._monitors = []  # type: List[Dict[str, int]]
+
         self.monitorenumproc = ctypes.WINFUNCTYPE(
             ctypes.wintypes.INT,
             ctypes.wintypes.DWORD,

tests/test_implementation.py

@@ -114,7 +114,7 @@ def test_entry_point(capsys, sct):
 
     fmt = "sct_{mon}-{date:%Y-%m-%d}.png"
     for opt in ("-o", "--out"):
-        main([opt, fmt])
+        main(["-m 1", opt, fmt])
         filename = fmt.format(mon=1, date=datetime.now())
         out, _ = capsys.readouterr()
         assert out.endswith(filename + "\n")