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Aug 23, 2019
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bpo-30826: Improve control flow examples #15407

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28 changes: 14 additions & 14 deletions Doc/tutorial/controlflow.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -66,20 +66,20 @@ they appear in the sequence. For example (no pun intended):
window 6
defenestrate 12

If you need to modify the sequence you are iterating over while inside the loop
(for example to duplicate selected items), it is recommended that you first
make a copy. Iterating over a sequence does not implicitly make a copy. The
slice notation makes this especially convenient::

>>> 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']

With ``for w in words:``, the example would attempt to create an infinite list,
inserting ``defenestrate`` over and over again.
Code that modifies a collection while iterating over that same collection can
be tricky to get right. Instead, it is usually more straight-forward to loop
over a copy of the collection or to create a new collection::
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The three lines are clearer and more correct in giving both strategies.

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You're happy with the proposed wording, correct?

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Yes. There is no checkbox for "(*) Approve either as is as a definite and acceptable improvement over the status quo or after possible further improvements based on my comments -- you decide."

In this case, you considered each suggestion and and gave a short coherent reason why not, one which I can consider when writing or reviewing other doc patches.

I appreciate you tackling some of these lingering doc issues which have seemingly been blocked by the quest for perfection even when improvement is clearly possible.


# Strategy: Iterate over a copy
for user, status in users.copy().items():
if status == 'inactive':
del users[user]

# Strategy: Create a new collection
active_users = {}
for user, status in users.items():
if status == 'active':
active_users[user] = status


.. _tut-range:
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