Support changing the line spacing.

src/escpos/constants.py

@@ -101,6 +101,13 @@ TXT_ALIGN_RT   = ESC + b'\x61\x02'  # Right justification
 TXT_INVERT_ON  = GS  + b'\x42\x01'  # Inverse Printing ON
 TXT_INVERT_OFF = GS  + b'\x42\x00'  # Inverse Printing OFF
 
+# Spacing
+LINESPACING_FUNCS = {
+  60: ESC + b'A',  # line_spacing/60 of an inch, 0 <= line_spacing <= 85
+  360: ESC + b'+', # line_spacing/360 of an inch, 0 <= line_spacing <= 255
+  180: ESC + b'3', # line_spacing/180 of an inch, 0 <= line_spacing <= 255
+}
+
 # Char code table
 CHARCODE_PC437  = ESC + b'\x74\x00'  # USA: Standard Europe
 CHARCODE_JIS    = ESC + b'\x74\x01'  # Japanese Katakana

src/escpos/escpos.py

@@ -565,6 +565,29 @@ class Escpos(object):
         else:
             self._raw(TXT_INVERT_OFF)
 
+    def line_spacing(self, spacing=30, divisor=180):
+        """ Set line character spacing.
+
+        There are different commands for setting the line spacing, using
+        a different denominator:
+
+        + line_spacing/360 of an inch, 0 <= line_spacing <= 255
+        3 line_spacing/180 of an inch, 0 <= line_spacing <= 255
+        A line_spacing/60 of an inch, 0 <= line_spacing <= 85
+
+        Some printers may not support all of them. The most commonly
+        available command (using a divisor of 180) is chosen.
+        """
+        if divisor not in LINESPACING_FUNCS:
+            raise ValueError("divisor must be either 360, 180 or 60")
+        if (divisor in [360, 180] \
+                and (not(0 <= spacing <= 255))):
+            raise ValueError("spacing must be a int between 0 and 255 when divisor is 360 or 180")
+        if divisor == 60 and (not(0 <= spacing <= 85)):
+            raise ValueError("spacing must be a int between 0 and 85 when divisor is 60")
+
+        self._raw(LINESPACING_FUNCS[divisor] + six.int2byte(spacing))
+
     def cut(self, mode=''):
         """ Cut paper.
 

test/test_functions.py

@@ -0,0 +1,20 @@
+from nose.tools import assert_raises
+from escpos.printer import Dummy
+
+
+def test_line_spacing_code_gen():
+    printer = Dummy()
+    printer.line_spacing(10)
+    assert printer.output == '\x1b3\n'
+
+
+def test_line_spacing_error_handling():
+    printer = Dummy()
+    with assert_raises(ValueError):
+      printer.line_spacing(divisor=44)
+    with assert_raises(ValueError):
+      printer.line_spacing(divisor=80, spacing=86)
+    with assert_raises(ValueError):
+      printer.line_spacing(divisor=360, spacing=256)
+    with assert_raises(ValueError):
+      printer.line_spacing(divisor=180, spacing=256)