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| author | Chris Jerdonek <chris.jerdonek@gmail.com> | 2012-10-16 02:44:47 (GMT) |
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| committer | Chris Jerdonek <chris.jerdonek@gmail.com> | 2012-10-16 02:44:47 (GMT) |
| commit | 4fab8f0e067772c4c13c86056c2b659cd8e5a812 (patch) | |
| tree | 3e17477b02bc9af2bf60cef0c02e81766fdff1bb /Doc/tutorial/datastructures.rst | |
| parent | f341317185ef7ec6d0cfb2ca93c9d253c3c75305 (diff) | |
| download | cpython-4fab8f0e067772c4c13c86056c2b659cd8e5a812.zip cpython-4fab8f0e067772c4c13c86056c2b659cd8e5a812.tar.gz cpython-4fab8f0e067772c4c13c86056c2b659cd8e5a812.tar.bz2 | |
Issue #16225: Add additional note to tutorial about changing sequence while looping.
Diffstat (limited to 'Doc/tutorial/datastructures.rst')
| -rw-r--r-- | Doc/tutorial/datastructures.rst | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/Doc/tutorial/datastructures.rst b/Doc/tutorial/datastructures.rst index 12b5c57..e008dd8 100644 --- a/Doc/tutorial/datastructures.rst +++ b/Doc/tutorial/datastructures.rst @@ -584,6 +584,19 @@ returns a new sorted list while leaving the source unaltered. :: orange pear +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: |