Add lazychain.py.

voussoirkit/lazychain.py

@@ -0,0 +1,35 @@
+import collections
+
+class LazyChain:
+    '''
+    You may be familiar with itertools.chain, which chains two iterables into
+    one. However, I wanted a data structure where I could add more and more
+    generators into the chain without repeatedly calling
+    `chain = itertools.chain(chain, more)`.
+    '''
+    def __init__(self):
+        self.iters = collections.deque()
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        while self.iters:
+            try:
+                return next(self.iters[0])
+            except StopIteration:
+                self.iters.popleft()
+        raise StopIteration()
+
+    def append(self, item):
+        '''
+        Add a single item to the chain.
+        '''
+        self.iters.append(iter((item,)))
+
+    def extend(self, sequence):
+        '''
+        Add the contents of a list, tuple, generator... to the chain.
+        Make sure not to exhaust the generator outside of this chain!
+        '''
+        self.iters.append(iter(sequence))