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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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Georg Brandl 2009-12-19 17:46:40 +00:00
parent 4d345ce1c9
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Doc/faq/design.rst
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@ -234,8 +234,10 @@ code breakage.
.. XXX talk about protocols? .. XXX talk about protocols?
Note that for string operations Python has moved from external functions (the .. note::
``string`` module) to methods. However, ``len()`` is still a function.
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? 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 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:: 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] value = dict[key]
else: else:
dict[key] = getvalue(key) dict[key] = getvalue(key)
value = dict[key] value = dict[key]
(In Python 2.0 and higher, you can code this as ``value = dict.setdefault(key, For this specific case, you could also use ``value = dict.setdefault(key,
getvalue(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? 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. # Callers will never provide a third parameter for this function.
def expensive (arg1, arg2, _cache={}): def expensive (arg1, arg2, _cache={}):
if _cache.has_key((arg1, arg2)): if (arg1, arg2) in _cache:
return _cache[(arg1, arg2)] return _cache[(arg1, arg2)]
# Calculate the value # Calculate the value