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  r76886 | georg.brandl | 2009-12-19 18:43:33 +0100 (Sa, 19 Dez 2009) | 1 line

  #7493: review of Design FAQ by Florent Xicluna.
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This commit is contained in:
Georg Brandl 2009-12-19 17:46:40 +00:00
parent 4d345ce1c9
commit bfe95ac098
1 changed files with 9 additions and 6 deletions

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@ -234,8 +234,10 @@ code breakage.
.. XXX talk about protocols?
Note that for string operations Python has moved from external functions (the
``string`` module) to methods. However, ``len()`` is still a function.
.. note::
For string operations, Python has moved from external functions (the
``string`` module) to methods. However, ``len()`` is still a function.
Why is join() a string method instead of a list or tuple method?
@ -306,14 +308,15 @@ 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 dict.has_key(key):
if key in dict(key):
value = dict[key]
else:
dict[key] = getvalue(key)
value = dict[key]
(In Python 2.0 and higher, you can code this as ``value = dict.setdefault(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
is evaluated in all cases.
Why isn't there a switch or case statement in Python?
@ -750,7 +753,7 @@ requested again. This is called "memoizing", and can be implemented like this::
# Callers will never provide a third parameter for this function.
def expensive (arg1, arg2, _cache={}):
if _cache.has_key((arg1, arg2)):
if (arg1, arg2) in _cache:
return _cache[(arg1, arg2)]
# Calculate the value