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author | Georg Brandl <georg@python.org> | 2012-03-17 15:58:12 (GMT) |
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committer | Georg Brandl <georg@python.org> | 2012-03-17 15:58:12 (GMT) |
commit | 2ba1428911370cb8c98572ac4ceb3b4ea2e04ad3 (patch) | |
tree | ee77a488d39bb9f5511e38da9133de75cc3117f4 /Doc/faq/design.rst | |
parent | 7add4eaa6d4a7ffd2f15821e962c8e6486deeef7 (diff) | |
parent | 12c3cd7c1f090cb055d395a5d54deba955af9d7b (diff) | |
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merge with 3.2
Diffstat (limited to 'Doc/faq/design.rst')
-rw-r--r-- | Doc/faq/design.rst | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/Doc/faq/design.rst b/Doc/faq/design.rst index 5441fd4..43ec692 100644 --- a/Doc/faq/design.rst +++ b/Doc/faq/design.rst @@ -284,8 +284,9 @@ Similar methods exist for bytes and bytearray objects. How fast are exceptions? ------------------------ -A try/except block is extremely efficient. Actually catching an exception is -expensive. In versions of Python prior to 2.0 it was common to use this idiom:: +A try/except block is extremely efficient if no exceptions are raised. Actually +catching an exception is expensive. In versions of Python prior to 2.0 it was +common to use this idiom:: try: value = mydict[key] @@ -296,11 +297,10 @@ expensive. In versions of Python prior to 2.0 it was common to use this idiom:: This only made sense when you expected the dict to have the key almost all the time. If that wasn't the case, you coded it like this:: - if mydict.has_key(key): + if key in mydict: value = mydict[key] else: - mydict[key] = getvalue(key) - value = mydict[key] + value = mydict[key] = getvalue(key) For this specific case, you could also use ``value = dict.setdefault(key, getvalue(key))``, but only if the ``getvalue()`` call is cheap enough because it |