diff options
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 bd661e2..36abc9c 100644 --- a/Doc/tutorial/datastructures.rst +++ b/Doc/tutorial/datastructures.rst @@ -589,6 +589,19 @@ 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: |