deque.popleft() is faster than list.pop(0), because the deque has been optimized to do popleft() approximately in O(1), while list.pop(0) takes O(n) (see deque objects). Comments and code in _collectionsmodule.c for deque and listobject.c for list provide implementation insights to explain the performance differences. Namely that a deque object “is composed of a doubly-linked list”, which … Read more
Yes, your understanding is correct. There is basically (very basically) a giant switch statement inside the CPython interpreter that says “if the current opcode is so and so, do this and that”. http://hg.python.org/cpython/file/3.3/Python/ceval.c#l790 Other implementations, like Pypy, have JIT compilation, i.e. they translate Python to machine codes on the fly.
It’s ironic, considering that Jython and Numeric (NumPy’s ancestor) were initiated by the same developer (Jim Hugunin, who then moved on to also initiate IronPython and now holds some kind of senior architect position at Microsoft, working on all kind of dynamic languages support for .NET and Silverlight), that there’s no really good way to … 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
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
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 has only been tested on Windows: You can do the following: import os os.startfile(“C:/Users/TestFile.txt”, “print”) This will start the file, in its default opener, with the verb ‘print’, which will print to your default printer.Only requires the os module which comes with the standard library
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