Class scopes are a bit strange in Python 3, but it’s for a good reason. In Python 2, the iteration variables (i and j in your examples) leaked out of list comprehensions and would be included in the outside scope. This is because they were developed early in Python 2’s design, and they were based … Read more
If you want to determine whether a value is exactly True (not just a true-like value), is there any reason to use if foo == True rather than if foo is True? If you want to make sure that foo really is a boolean and of value True, use the is operator. Otherwise, if the … Read more
For this purpose, I’ve used a repeating MD5 hash, since the intention of a hashing function is a cross-platform one-to-one transformation, so it will always be the same on different platforms. import md5 def repeatable_random(seed): hash = seed while True: hash = md5.md5(hash).digest() for c in hash: yield ord(c) def test(): for i, v in … Read more
Sets and dicts are optimized for different use-cases. The primary use of a set is fast membership testing, which is order agnostic. For dicts, cost of the lookup is the most critical operation, and the key is more likely to be present. With sets, the presence or absence of an element is not known in … Read more
As a caveat, everything in this answer is based on what I’ve gleaned from looking over the implementation you linked. It seems that the standard implementation of a tuple is simply as an array. However, there are a bunch of optimizations in place to speed things up. First, if you try to make an empty … Read more
This is a quirk of how the CPython implementation chooses to cache string literals. String literals with the same contents may refer to the same string object, but they don’t have to. ‘string’ happens to be automatically interned when ‘string ‘ isn’t because ‘string’ contains only characters allowed in a Python identifier. I have no … Read more
No, sets are still unordered. You can verify this just by displaying a set that should have a “well-defined hash order”1 to make sure we don’t accidentally get a set that looks ordered but actually isn’t: >>> a_set = {3,2,1} >>> a_set {1, 2, 3} >>> list(a_set) [1, 2, 3] If it were ordered you … Read more
When you run code in a .py script, the entire file is compiled into a code object before execution. In this case, CPython is able to make certain optimizations – like reusing the same instance for the integer 300. You could also reproduce that in the REPL, by executing code in a context more closely … Read more
The package Python for.NET and the Python Implementation IronPython now work the same way. Example for a C# DLL MyDll.dll: import clr clr.AddReference(‘MyDll’) from MyNamespace import MyClass my_instance = MyClass() See this post for more details.
I think you’re seeing over-allocation patterns this is a sample from the source: /* This over-allocates proportional to the list size, making room * for additional growth. The over-allocation is mild, but is * enough to give linear-time amortized behavior over a long * sequence of appends() in the presence of a poorly-performing * system … Read more