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Posts by Karl Knechtel
When I have tried to read technical explanations of the syntax rules for programming languages, and when I am trying to decipher error messages, I often encounter the terms expression and statement...
Before attempting this, make sure it makes sense in context. In a few particular situations, it would be better to take a different approach rather than using the normal tools for composing or f...
Would it discourage others from posting answers, if they saw that a question had an answer with a "works for me" indication applied immediately? (More so than just seeing an immediate, comprehensiv...
Consider this code example: def example(param=[]): param.append('value') print(param) When example is repeatedly called with an existing list, it repeatedly appends to the list, as ...
My actual motivation is to understand the semantics of the .gitignore file syntax in precise detail, for a program which is expected to emulate them as accurately as possible. However, while coming...
These two uses of if are different The if at the end of a list comprehension syntax: [num for num in hand if num != 11] is a filter; its purpose is to decide whether or not the resulting list ...
Import modules rather than names first to avoid a circular reference in the import statements; then use forward declarations, as before, to avoid a circular reference in the type annotations - like...
I want to write one or more self-answered Q&As on the topic of text encoding in Python, to serve as canonicals and preempt future lower-quality questions. I can think of the following things th...
Terminology "Mutable default argument" means exactly what the individual words would suggest: it's an argument which is supplied as the default value for that parameter, which also is mutable. To ...
Never Too Late Due to, shall we say, recent AI-related hallucinations, pretty much everything that was possible PR-wise in 2019 is possible for this site again. People are leaving Stack Overflow a...
I think the framing of this question (and the prior discussion) is wrong, and I think that conditions have evolved since it was originally asked - in particular, we can now see how articles have tu...
So far, existing Meta discussion seems to have at least hinted at the possibility of using separate categories here: To shuffle closed questions out of the way (globally for Codidact) (also) Fo...
How to do it Yes, Python has an equivalent operator. However, it's spelled with keywords rather than punctuation, and it uses a different order of operands. It looks like: condition_value if some...
Starting up Python There are several key ways to use the python command from the command line: python by itself starts a REPL that allows typing in and running Python code on the fly, one sta...
No. Terms like "too generic", "unclear", "too broad", "off topic" are absolutely not euphemisms for "stupid question, go away". They mean what they say; and when they are used Somewhere Else, mult...
A well-known easter egg in Python displays some ideas about writing good Python code, credited to Tim Peters (one of the core developers). This question is about the last: Namespaces are one hon...
Workarounds Avoiding mutation Because problems are only caused by actually mutating the default argument, the simplest way to avoid problems is to... not do that. Pythonic code obeys command-quer...
Looking back at my own Q&A How can I build a string from smaller pieces?, the answer is incredibly long. I'm essentially showing five different ways to solve the problem - because they all exis...
Use at to schedule the command, using subprocess from Python to invoke at. It doesn't even require shell=True. For example: import shlex, subprocess subprocess.run( # `at` command to run n...
Possible justifications It may make sense to use a mutable default argument in the following situations: For simplicity Consider for example an argument that should be some kind of mapping, wher...
As the author, this is my defense. Design and modeling are on-topic The site topicality documentation explicitly includes "Software design, architecture, or modeling" as on topic. There doesn't s...
Root cause ModuleNotFoundError is a kind of ImportError. It occurs when Python code tries to use an absolute import, but can't find the named module - just as the name suggests. (Failed relative i...
The fundamental problem here is that it is already ambiguous where the "end" of the data in the buffer is. Strings can be empty (have zero length as reported by strlen); as such, buffer could equal...
Suppose I have some code in a file myscript.py like: def my_function(): print("Test") What steps do I need to take in order to make my_function run? That is to say: how do I get Python to ...
A compromise exists between automatically inferring package names (unreliable and potentially dangerous) and writing out an explicit separate requirements.txt file: script-running tools such as pip...
