From c166aa043016921e5c3910ce4368af6d87d1afa0 2012-09-01 21:03:36
From: MinRK <benjaminrk@gmail.com>
Date: 2012-09-01 21:03:36
Subject: [PATCH] Backport PR #2261: Fix: longest_substr([]) -> ''

Previously the algorithm used to find the longest common starting substring
unintentionally raised an error when it was called on an empty list.

This should fix the issue of an error being raised when running %paste
on an empty clipboard (#2252).

---

diff --git a/IPython/utils/tests/test_text.py b/IPython/utils/tests/test_text.py
index 8822262..fa4c7fb 100644
--- a/IPython/utils/tests/test_text.py
+++ b/IPython/utils/tests/test_text.py
@@ -149,6 +149,9 @@ def test_long_substr2():
     data = ['abc', 'abd', 'abf', 'ab']
     nt.assert_equals(text.long_substr(data), 'ab')
 
+def test_long_substr_empty():
+    data = []
+    nt.assert_equals(text.long_substr(data), '')
 
 def test_strip_email():
     src = """\
diff --git a/IPython/utils/text.py b/IPython/utils/text.py
index f66962a..b53f826 100644
--- a/IPython/utils/text.py
+++ b/IPython/utils/text.py
@@ -553,7 +553,7 @@ def long_substr(data):
             for j in range(len(data[0])-i+1):
                 if j > len(substr) and all(data[0][i:i+j] in x for x in data):
                     substr = data[0][i:i+j]
-    else:
+    elif len(data) == 1:
         substr = data[0]
     return substr