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Issue #16225: Backport from 3.2: Add additional note to tutorial about looping.

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Chris Jerdonek 2012-10-15 20:01:38 -07:00
parent fd6d3b149f
commit 0cffd6be56
2 changed files with 24 additions and 11 deletions
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13
Doc/tutorial/datastructures.rst
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@ -645,6 +645,19 @@ retrieved at the same time using the :meth:`iteritems` method. ::
gallahad the pure
robin the brave
To change a sequence you are iterating over while inside the loop (for
example to duplicate certain items), it is recommended that you first make
a copy. Looping over a sequence does not implicitly make a copy. The slice
notation makes this especially convenient::
>>> words = ['cat', 'window', 'defenestrate']
>>> for w in words[:]: # Loop over a slice copy of the entire list.
... if len(w) > 6:
... words.insert(0, w)
...
>>> words
['defenestrate', 'cat', 'window', 'defenestrate']
.. _tut-conditions: