When you run b.pop(0), Python moves all the elements back by one as you might expect. This takes O(n) time. When you del b[0], Python simply increases the start pointer of the object by 1. In both cases, PyByteArray_Resize is called to adjust the size. When the new size is smaller than half the allocated … Read more
As already mentioned in the comments, if you use s.__contains__(“XYZ”) you get a result that is more similar to s.startswith(“XYZ”) because it needs to take the same route: Member lookup on the string object, followed by a function call. This is usually somewhat expensive (not enough that you should worry about of course). On the … Read more
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
Sorry, not possible. Dict literals and dict comprehensions map to the built-in dict type, in a way that’s hardcoded at the C level. That can’t be overridden. You can use this as an alternative, though: OrderedDict((i, i * i) for i in range(3)) Addendum: as of Python 3.6, all Python dictionaries are ordered. As of … 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 is because bool is a subclass of int in both Python 2 and 3. >>> issubclass(bool, int) True But the int implementation has changed. In Python 2, int was the one that was 32 or 64 bits, depending on the system, as opposed to arbitrary-length long. In Python 3, int is arbitrary-length – the … Read more
In [50]: import platform In [52]: platform.python_implementation() Out[52]: ‘CPython’
My results were similar to yours: the code that uses intermediate variables was consistently at least 10-20 % faster in Python 3.4. However when I used IPython on the very same Python 3.4 interpreter, I got these results: In [1]: %timeit -n10000 -r20 tuple(range(2000)) == tuple(range(2000)) 10000 loops, best of 20: 74.2 µs per loop … Read more
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
python-dev python-dev contains the header files you need to build Python extensions. lxml lxml is a Python C-API extension that is compiled when you do pip install lxml. The lxml sources have at least something like #include <Python.h> in the code. The compiler looks for the header file Python.h during compilation, hence those header files … Read more