Best way to 'intelligently' reset memoized property values in Python when dependencies change Question: I’m writing a class with various attributes that I only want to calculate when necessary (lazy evaluation). However, more importantly, I want to make sure that ‘stale’ values are not returned if any of the attributes that their calculation depended on …
Lazy evaluation in Python Question: What is lazy evaluation in Python? One website said : In Python 3.x the range() function returns a special range object which computes elements of the list on demand (lazy or deferred evaluation): >>> r = range(10) >>> print(r) range(0, 10) >>> print(r[3]) 3 What is meant by this? Asked …
How to implement a lazy setdefault? Question: One minor annoyance with dict.setdefault is that it always evaluates its second argument (when given, of course), even when the first the first argument is already a key in the dictionary. For example: import random def noisy_default(): ret = random.randint(0, 10000000) print ‘noisy_default: returning %d’ % ret return …
Does Python evaluate if's conditions lazily? Question: For example, if I have the following statement: if( foo1 or foo2) … … if foo1 is true, will python check the condition of foo2? Asked By: ogama8 || Source Answers: Yes, Python evaluates boolean conditions lazily. The docs say, The expression x and y first evaluates x; …
Why is django's settings object a LazyObject? Question: Looking in django.conf I noticed that settings are implemented like this: class LazySettings(LazyObject): … What is the rationale behind making settings objects lazy? Asked By: pseudosudo || Source Answers: Its a proxy object that abstracts the actual settings files, and makes it light weight until you actually …
How do lexical closures work? Question: While I was investigating a problem I had with lexical closures in Javascript code, I came along this problem in Python: flist = [] for i in xrange(3): def func(x): return x * i flist.append(func) for f in flist: print f(2) Note that this example mindfully avoids lambda. It …
