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copied!<p>This will add terms until <code>dic</code> does not contain <code>key</code>.</p> <pre><code>dic = {'had': ['a', 'little'], 'Mary': ['had', 'a'], 'a': ['little', 'lamb.']} key = 'Mary' res = [] while True: try: res.extend(dic[key]) key = dic[key][-1] except KeyError: break print ' '.join(res) </code></pre> <p>This yields:</p> <pre><code>['had', 'a', 'little', 'lamb.'] </code></pre> <p>Be aware: You will enter an infinite loop if all values also are a key. You will also encounter this if there is a repeating sequence in your dictionary, such as </p> <pre><code>{'a': ['b', 'c'], 'b': ['a', 'c'], 'c': ['a', 'b'], 'foo': ['bar', 'foobar']} </code></pre> <p>To avoid this, you could do one out of two things:</p> <ol> <li>Set a maximum iteration value</li> <li>Stop the iteration when you encounter a key that previously have been seen.</li> </ol> <p><strong>Maximum iteration value:</strong></p> <pre><code>dic = {'had': ['a', 'little'], 'Mary': ['had', 'a'], 'a': ['little', 'lamb.']} key = 'Mary' res = [] max_iterations = 10 i = 0 while i < max_iterations try: res.extend(dic[key]) key = dic[key][-1] except KeyError: break i += 1 if i > max_iterations: break print ' '.join(res) </code></pre> <p><strong>Stop at previously seen key</strong></p> <pre><code>dic = {'had': ['a', 'little'], 'Mary': ['had', 'a'], 'a': ['little', 'lamb.']} key = 'Mary' res = [] seen_keys = [] while True: if key in seen_keys: break try: res.extend(dic[key]) seen_keys.append(key) key = dic[key][-1] except KeyError: break print ' '.join(res) </code></pre>

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