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Welcome to Software Development on Codidact!

Will you help us build our independent community of developers helping developers? We're small and trying to grow. We welcome questions about all aspects of software development, from design to code to QA and more. Got questions? Got answers? Got code you'd like someone to review? Please join us.

Posts by Karl Knechtel‭

113 posts
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+15 −0
Q&A Why are list comprehensions written differently if you use else?

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 ...

posted 3y ago by Karl Knechtel‭  ·  edited 7mo ago by wjandrea‭

Answer
88%
+13 −0
Q&A What are statements and expressions?

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...

4 answers  ·  posted 3y ago by Karl Knechtel‭  ·  last activity 3y ago by Dirk Herrmann‭

Question terminology language-agnostic
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+9 −0
Meta Call for moderators (2025)

Sure, I'll step up for this, since nobody else has yet. I think my credentials speak for themselves, but just in case: I'm an accomplished Python developer with a long history of helping people ou...

posted 1y ago by Karl Knechtel‭

Answer
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Q&A Understanding mutable default arguments in Python

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 ...

4 answers  ·  posted 3y ago by Karl Knechtel‭  ·  last activity 3y ago by matthewsnyder‭

Question python default-argument mutability
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+9 −0
Meta On self-answered questions, is it inappropriate to mark my own answer "Works for me" immediately?

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...

3 answers  ·  posted 3y ago by Karl Knechtel‭  ·  last activity 3y ago by matthewsnyder‭

Question discussion policy site-culture self-answered-questions
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+9 −0
Q&A How can I build a string from smaller pieces?

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...

posted 3y ago by Karl Knechtel‭  ·  edited 3y ago by Karl Knechtel‭

Answer
84%
+9 −0
Meta How can we grow this community?

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...

posted 3y ago by Karl Knechtel‭

Answer
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+8 −0
Q&A Git-ignoring files with special characters in their names, especially newlines

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...

1 answer  ·  posted 3y ago by Karl Knechtel‭  ·  last activity 3y ago by Peter Taylor‭

Question git linux gitignore
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+7 −0
Meta What questions are we most urgently missing?

Context: As you may be aware, recent poorly received changes on Some Other website are likely to have pushed a lot of their regulars to a breaking point. Nowadays, Codidact (and specifically S...

4 answers  ·  posted 7mo ago by Karl Knechtel‭  ·  last activity 6mo ago by hkotsubo‭

Question discussion stack-overflow brainstorming
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+7 −0
Meta What is the policy regarding cross-posting here and on StackOverflow?

These are just my thoughts, not an official policy prescription as a moderator. If you're asking because you need an answer, please ask here first, and only cross-post to Stack Overflow if you...

posted 1y ago by Karl Knechtel‭

Answer
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+7 −0
Q&A Choosing between multiple Python installations (environments) on the same computer

This answer assumes only installations of the reference "CPython" implementation, as provided by the official website at https://www.python.org. Other installations - such as those provided by th...

posted 2y ago by Karl Knechtel‭  ·  edited 25d ago by Moshi‭

Answer
81%
+7 −0
Q&A How and where does Python code start running? How can I control that?

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 ...

2 answers  ·  posted 2y ago by Karl Knechtel‭  ·  last activity 1d ago by jhonAHILLL‭

Question python startup entry-point
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Q&A Understanding mutable default arguments in Python

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 ...

posted 3y ago by Karl Knechtel‭  ·  edited 3y ago by Karl Knechtel‭

Answer
80%
+6 −0
Q&A Why does my regex "match" at the beginning of the string, but not at the end?

Yes, re.match matches lines that start with the described pattern: If zero or more characters at the beginning of string match the regular expression pattern, return a corresponding Match. To...

posted 1y ago by Karl Knechtel‭  ·  edited 5mo ago by Karl Knechtel‭

Answer
80%
+6 −0
Q&A Choosing between multiple Python installations (environments) on the same computer

I have multiple installations of Python on my machine. When I run Python, what determines which installation is used? How can I control this?

1 answer  ·  posted 2y ago by Karl Knechtel‭  ·  last activity 25d ago by Moshi‭

Question python installation runtime-environment
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Meta Don't close questions for lack of detail/confusion

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...

posted 2y ago by Karl Knechtel‭

Answer
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Meta What categories could we benefit from having?

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...

2 answers  ·  posted 3y ago by Karl Knechtel‭  ·  last activity 4mo ago by Ooker‭

Question discussion site-culture categories
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+6 −0
Meta How should I organize material about text encoding in Python into questions?

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...

3 answers  ·  posted 3y ago by Karl Knechtel‭  ·  last activity 3y ago by Karl Knechtel‭

Question discussion scope content-quality
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+6 −0
Q&A How can I properly type-hint methods in different files that would lead to circular imports?

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...

posted 3y ago by Karl Knechtel‭  ·  edited 3y ago by Karl Knechtel‭

Answer
77%
+5 −0
Q&A How does the strict aliasing rule enable or prevent compiler optimizations?

Inspired by https://meta.stackoverflow.com/questions/432242, and the relevant main-space questions. I have heard that C and C++ something called the "strict aliasing rule", which means for exa...

2 answers  ·  posted 2y ago by Karl Knechtel‭  ·  last activity 1y ago by Lundin‭

Question c c++ undefined-behavior optimization strict-aliasing
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Q&A Why does Pip display "error: externally-managed-environment", and what can I do about it?

My (non-Windows) operating system came with Python, but that Python didn't include Pip. I followed instructions to install Pip for the included Python, using my system's package manager. But now w...

2 answers  ·  posted 2y ago by Karl Knechtel‭  ·  last activity 2y ago by Alexei‭

Question python linux pip
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+5 −0
Meta Is my question a duplicate? What now?

As part of a general effort to produce basic Q&As for Python, recently I've been focused on issues related to starting up an interpreter and running the code - so, questions about setting up an...

0 answers  ·  posted 2y ago by Karl Knechtel‭

Question discussion duplicate-questions canonicals self-answered-questions
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Q&A Understanding Virtual Environments for Python

Why The most important ideas behind virtual environments are: Since there is a separate site-packages, you can isolate the dependencies of your project. This is especially important for testi...

posted 2y ago by Karl Knechtel‭

Answer
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+5 −0
Q&A Does Python have a "ternary operator" (conditional evaluation operator like "?:" in other languages)?

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...

posted 3y ago by Karl Knechtel‭

Answer
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+5 −0
Meta Should asking about book recommendations directly connected to software development be on-topic?

Are books special? When I see a question like this, I naturally transform it into a more general question about resources. Printed books aren't necessarily the best way to learn about programming ...

posted 3y ago by Karl Knechtel‭  ·  edited 3y ago by Karl Knechtel‭

Answer