GapString class

gapstr.py

@@ -0,0 +1,138 @@
+#! /usr/bin/python
+
+"""Functions to treat a list as a string with gaps.
+
+Lists should have only string and integer items.
+
+"""
+
+import __init__
+import sys
+
+class GapString:
+    def __init__(self, drop='?'):
+        self.contents = []
+        self.length = 0
+        self.drop = drop
+
+    def __len__(self):
+        return self.length
+
+    def __repr__(self):
+        return '<GapString of length %d>' % self.length
+
+    def append(self, i):
+        self.contents.append(i)
+        if isinstance(i, int):
+            self.length += i
+        else:
+            self.length += len(i)
+
+    def __str__(self):
+        ret = []
+        for i in self.contents:
+            if isinstance(i, int):
+                ret.append(self.drop * i)
+            else:
+                ret.append(i)
+        return ''.join(ret)
+
+    def hexdump(self, fd=sys.stdout):
+        offset = 0
+
+        d = __init__.HexDumper(fd)
+        for i in self.contents:
+            if isinstance(i, int):
+                for j in range(i):
+                    d.dump_drop()
+            else:
+                for c in i:
+                    d.dump_chr(c)
+        d.flush()
+
+    def extend(self, other):
+        self.contents += other.contents
+        self.length += other.length
+
+    def __getslice__(self, start, end):
+        end = min(self.length, end)
+
+        new = self.__class__(self.drop)
+        new.contents = self.contents[:]
+        new.length = end - start
+        l = self.length - new.length - start
+
+        # Trim off the beginning
+        while start >= 0:
+            i = new.contents.pop(0)
+            if isinstance(i, int):
+                start -= i
+                if start < 0:
+                    new.contents.insert(0, -start)
+            else:
+                start -= len(i)
+                if start < 0:
+                    new.contents.insert(0, i[start:])
+
+        # Trim off the end
+        while l >= 0:
+            i = new.contents.pop()
+            if isinstance(i, int):
+                l -= i
+                if l < 0:
+                    new.contents.append(-l)
+            else:
+                l -= len(i)
+                if l < 0:
+                    new.contents.append(i[:-l])
+
+        return new
+
+    def __add__(self, other):
+        if isinstance(other, str):
+            self.append(other)
+        else:
+            new = self.__class__(self.drop)
+            new.extend(self)
+            new.extend(other)
+            return new
+
+    def __xor__(self, mask):
+        if isinstance(mask, int):
+            mask = [mask]
+        masklen = len(mask)
+
+        new = self.__class__(self.drop)
+        for i in self.contents:
+            if isinstance(i, int):
+                new.append(i)
+            else:
+                r = []
+                offset = len(new) % masklen
+                for c in i:
+                    o = ord(c)
+                    r.append(chr(o ^ mask[offset]))
+                    offset = (offset + 1) % masklen
+                new.append(''.join(r))
+        return new
+
+
+
+if __name__ == '__main__':
+    gs = GapString()
+    gs.append('hi')
+    assert str(gs) == 'hi'
+    assert str(gs[:40]) == 'hi'
+    gs.append(3)
+    assert str(gs) == 'hi???'
+    assert str(gs[:40]) == 'hi???'
+    assert str(gs[:3]) == 'hi?'
+    assert str(gs[-4:]) == 'i???'
+    assert str(gs + gs) == 'hi???hi???'
+    assert str(gs ^ 1) == 'ih???'
+
+    gs = GapString()
+    gs.append('123456789A')
+    assert str(gs[:4]) == '1234'
+    assert len(gs[:4]) == 4
+    assert len(gs[6:]) == 4