Ensure QR codes have a border large enough (#235)

*  Ensure QR codes have a border large enough
(The QR code spec requires a border at least 4*box_size thick but we can't
 just set border=16 because that results in a QR code more than 255px tall
 and I'm not yet ready to use fullimage() as a backend for it)
This fix was originally commited by Stephan Sokolow on 2014-05-22
* Let the user print stuff using qr example
* fix tests

examples/qr_code.py

@@ -0,0 +1,19 @@
+import sys
+
+from escpos.printer import Usb
+
+
+def usage():
+    print("usage: qr_code.py <content>")
+
+
+if __name__ == '__main__':
+    if len(sys.argv) != 2:
+        usage()
+        sys.exit(1)
+
+    content = sys.argv[1]
+
+    # Adapt to your needs
+    p = Usb(0x0416, 0x5011, profile="POS-5890")
+    p.qr(content)

src/escpos/escpos.py

@@ -211,7 +211,10 @@ class Escpos(object):
             qr_img = qr_code.make_image()
             im = qr_img._img.convert("RGB")
             # Convert the RGB image in printable image
+            self.text('\n')
             self.image(im)
+            self.text('\n')
+            self.text('\n')
             return
         # Native 2D code printing
         cn = b'1'  # Code type for QR code

test/test_function_qr_native.py

@@ -86,9 +86,11 @@ def test_image():
     instance = printer.Dummy()
     instance.qr("1", native=False, size=1)
     print(instance.output)
-    expected = b'\x1dv0\x00\x03\x00\x17\x00\x00\x00\x00\x7f]\xfcA\x19\x04]it]et' \
+    expected = b'\x1bt\x00\n' \
+        b'\x1dv0\x00\x03\x00\x17\x00\x00\x00\x00\x7f]\xfcA\x19\x04]it]et' \
         b']ItA=\x04\x7fU\xfc\x00\x0c\x00y~t4\x7f =\xa84j\xd9\xf0\x05\xd4\x90\x00' \
-        b'i(\x7f<\xa8A \xd8]\'\xc4]y\xf8]E\x80Ar\x94\x7fR@\x00\x00\x00'
+        b'i(\x7f<\xa8A \xd8]\'\xc4]y\xf8]E\x80Ar\x94\x7fR@\x00\x00\x00' \
+        b'\n\n'
     assert(instance.output == expected)