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Diffstat (limited to 'Doc/faq')
| -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 e45aaaa..87cc942 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 |