How does asyncio work? Before answering this question we need to understand a few base terms, skip these if you already know any of them. Generators Generators are objects that allow us to suspend the execution of a python function. User curated generators are implement using the keyword yield. By creating a normal function containing … Read more
A comment in the Python source code for float objects acknowledges that: Comparison is pretty much a nightmare This is especially true when comparing a float to an integer, because, unlike floats, integers in Python can be arbitrarily large and are always exact. Trying to cast the integer to a float might lose precision and … Read more
Summary Tuples tend to perform better than lists in almost every category: Tuples can be constant folded. Tuples can be reused instead of copied. Tuples are compact and don’t over-allocate. Tuples directly reference their elements. Tuples can be constant folded Tuples of constants can be precomputed by Python’s peephole optimizer or AST-optimizer. Lists, on the … Read more
It blocks the thread. If you look in Modules/timemodule.c in the Python source, you’ll see that in the call to floatsleep(), the substantive part of the sleep operation is wrapped in a Py_BEGIN_ALLOW_THREADS and Py_END_ALLOW_THREADS block, allowing other threads to continue to execute while the current one sleeps. You can also test this with a … Read more
Firstly, you can del other things besides local variables del list_item[4] del dictionary[“alpha”] Both of which should be clearly useful. Secondly, using del on a local variable makes the intent clearer. Compare: del foo to foo = None I know in the case of del foo that the intent is to remove the variable from … Read more
Take a look at this: >>> a = 256 >>> b = 256 >>> id(a) 9987148 >>> id(b) 9987148 >>> a = 257 >>> b = 257 >>> id(a) 11662816 >>> id(b) 11662828 Here’s what I found in the Python 2 documentation, “Plain Integer Objects” (It’s the same for Python 3): The current implementation keeps … Read more
Are dictionaries ordered in Python 3.6+? They are insertion ordered[1]. As of Python 3.6, for the CPython implementation of Python, dictionaries remember the order of items inserted. This is considered an implementation detail in Python 3.6; you need to use OrderedDict if you want insertion ordering that’s guaranteed across other implementations of Python (and other … Read more
In Python, what is the purpose of __slots__ and what are the cases one should avoid this? TLDR: The special attribute __slots__ allows you to explicitly state which instance attributes you expect your object instances to have, with the expected results: faster attribute access. space savings in memory. The space savings is from Storing value … Read more
The property() function returns a special descriptor object: >>> property() <property object at 0x10ff07940> It is this object that has extra methods: >>> property().getter <built-in method getter of property object at 0x10ff07998> >>> property().setter <built-in method setter of property object at 0x10ff07940> >>> property().deleter <built-in method deleter of property object at 0x10ff07998> These act as … Read more
The Python 3 range() object doesn’t produce numbers immediately; it is a smart sequence object that produces numbers on demand. All it contains is your start, stop and step values, then as you iterate over the object the next integer is calculated each iteration. The object also implements the object.__contains__ hook, and calculates if your … Read more