From 458120dd40db6b4df55a4e96b650e16798ef06a0 Mon Sep 17 00:00:00 2001
From: cinap_lenrek <cinap_lenrek@localhost>
Date: Tue, 3 May 2011 11:25:13 +0000
Subject: add hg and python

---
 sys/src/cmd/python/Demo/classes/Rev.py | 95 ++++++++++++++++++++++++++++++++++
 1 file changed, 95 insertions(+)
 create mode 100755 sys/src/cmd/python/Demo/classes/Rev.py

(limited to 'sys/src/cmd/python/Demo/classes/Rev.py')

diff --git a/sys/src/cmd/python/Demo/classes/Rev.py b/sys/src/cmd/python/Demo/classes/Rev.py
new file mode 100755
index 000000000..7fd78e03e
--- /dev/null
+++ b/sys/src/cmd/python/Demo/classes/Rev.py
@@ -0,0 +1,95 @@
+'''
+A class which presents the reverse of a sequence without duplicating it.
+From: "Steven D. Majewski" <sdm7g@elvis.med.virginia.edu>
+
+It works on mutable or inmutable sequences.
+
+>>> chars = list(Rev('Hello World!'))
+>>> print ''.join(chars)
+!dlroW olleH
+
+The .forw is so you can use anonymous sequences in __init__, and still
+keep a reference the forward sequence. )
+If you give it a non-anonymous mutable sequence, the reverse sequence
+will track the updated values. ( but not reassignment! - another
+good reason to use anonymous values in creating the sequence to avoid
+confusion. Maybe it should be change to copy input sequence to break
+the connection completely ? )
+
+>>> nnn = range(3)
+>>> rnn = Rev(nnn)
+>>> for n in rnn: print n
+...
+2
+1
+0
+>>> for n in range(4, 6): nnn.append(n)   # update nnn
+...
+>>> for n in rnn: print n     # prints reversed updated values
+...
+5
+4
+2
+1
+0
+>>> nnn = nnn[1:-1]
+>>> nnn
+[1, 2, 4]
+>>> for n in rnn: print n     # prints reversed values of old nnn
+...
+5
+4
+2
+1
+0
+
+#
+>>> WH = Rev('Hello World!')
+>>> print WH.forw, WH.back
+Hello World! !dlroW olleH
+>>> nnn = Rev(range(1, 10))
+>>> print nnn.forw
+[1, 2, 3, 4, 5, 6, 7, 8, 9]
+>>> print nnn.back
+[9, 8, 7, 6, 5, 4, 3, 2, 1]
+
+>>> rrr = Rev(nnn)
+>>> rrr
+<1, 2, 3, 4, 5, 6, 7, 8, 9>
+
+'''
+
+class Rev:
+    def __init__(self, seq):
+        self.forw = seq
+        self.back = self
+
+    def __len__(self):
+        return len(self.forw)
+
+    def __getitem__(self, j):
+        return self.forw[-(j + 1)]
+
+    def __repr__(self):
+        seq = self.forw
+        if isinstance(seq, list):
+            wrap = '[]'
+            sep = ', '
+        elif isinstance(seq, tuple):
+            wrap = '()'
+            sep = ', '
+        elif isinstance(seq, str):
+            wrap = ''
+            sep = ''
+        else:
+            wrap = '<>'
+            sep = ', '
+        outstrs = [str(item) for item in self.back]
+        return wrap[:1] + sep.join(outstrs) + wrap[-1:]
+
+def _test():
+    import doctest, Rev
+    return doctest.testmod(Rev)
+
+if __name__ == "__main__":
+    _test()
-- 
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