SICP in Python

It does make sense to evaluate the default value for the parameter at the point of definition for serveral reasons. First of all, the default value does not have to be a literal value, and if you wanted it to be evaluated at call time the function would need to capture all of the default values in a closure.

  default = 10
  def foo(x=default):
      return x
  default = 20
  assert foo() == 10

I think tat makes a lot of sense.

It could also be that the default value is a more ocmplex expression, we could use a function to generate a default argument.

  def foo(x=create_default(y, z))

By evaluating it at definition time we only have to evaluate the expression once and not have this weird lazy expression.

And yes it is used, for example the fastapi Dependency Injection system has been build quite cleverly using the ability to construct default values

https://fastapi.tiangolo.com/tutorial/query-params-str-valid...

Yes it is one of those things you just have to learn, but there are tons of stuff like that in most programming languages.

Indeed, a download and quick look shows that the book has a lot more content than just a sequence of lessons. I've immersed in the foreword, and enjoying it greatly. The best textbooks are not just informative, but written to be enjoyed as literature.

It's a classic for that reason. Enjoy!

here's my other comment that talks about this: https://news.ycombinator.com/item?id=23008968

even among dynamically typed languages, python is terrible. it has no real way to build up new types in a principled way, and you have to result to using (and abusing) the class system, which is hack after hack.

python also ignored and continued to ignore things that already existed in languages and advances. it also doesn't really like using data-type driven development. go ahead and search for "python records". you'll get nothing, and the best reference is a blog post (https://dbader.org/blog/records-structs-and-data-transfer-ob...) that leads you to a wide variety of solutions, all inconsistent with each other and not conventionally used. now search google and literally the top result for each query is the following:

"f# records" (https://docs.microsoft.com/en-us/dotnet/fsharp/language-refe...)

"elixir records" (https://hexdocs.pm/elixir/Record.html)

"clojure records" (https://clojuredocs.org/clojure.core/defrecord)

"racket lang records" (https://docs.racket-lang.org/rebellion/Records.html)

another area that python doesn't take seriously is scoping. the scoping rules and exceptions are complex, and this makes the language very dangerous. i mentioned one in the other comment i linked. python has weird scoping stuff with lambdas. python even has a keyword that makes a locally bound variable available in the calling scope (https://docs.python.org/3/reference/simple_stmts.html#nonloc...). no thank you. this is absolutely terrible design, and yes, i have seen it in production code (not written by me). just search "python scoping" or "python nonlocal", and you'll come across people confused by a plethora of edge cases.

python is just complicated. it has no simple core. it is a huge lump of stuff. both f# and racket are definitely more complicated than python in that they have behavior and features far exceeding python. however, they are principled. in one way, they have very simple core languages such that if you ignore all the fancy stuff, you can still write beautiful, reliable code with the simply designed core language. as you move to the more complicated stuff, you utilized this simple core over and over to build software that is still understandable. it allows you to build predictable software.

another area of principles i look for in a language are why it was created and what are the motivations of its creator(s). f# was created to bring a functional language to .net to utilize .net's vast functionality and test .net's language making and support capability. the development originally started with haskell but transitioned to ocaml since the model matched better with .net. don syme is a very practical language designer and an actual computer scientist. here is a draft of a paper by him about the history of f# (https://fsharp.org/history/hopl-final/hopl-fsharp.pdf). it's a useful read. racket was created to extend scheme into a new language that fully adopted language-oriented programming (lop) and had supporting libraries for normal development. this means taking an extremely principled language and extending it to support a new paradigm of software development in a principled, controlled way. see the paper a programmable programming language (https://cacm.acm.org/magazines/2018/3/225475-a-programmable-...). the authors of racket are also computer scientists and care about robust software development. python was created by someone interested in esoteric languages (ABC) and in creating a systems scripting language as a hobby project. the creator resisted and continued to resist many already existing language designs and features (found in scheme and ML-dialects such as SML). for example, lambda, map, filter, and reduce only exist in python because he begrudgingly accepted patches that someone else did. another example of unprincipled-ness is the creator's seemingly proud declaration to use multi-line string literals as multi-line comments since python did not have and still does not have multi-line comment support (https://twitter.com/gvanrossum/status/112670605505077248).

these things alone make me wholly not interested in python. i want to use a language that was created for a reason and in a principled way that solves a problem that i am facing. i also feel i need to agree with the reasons and also the philosophy of the language designers. none of this exists for me in python.

the early history of f# (https://fsharp.org/history/hopl-final/hopl-fsharp.pdf)

a programmable programming language (https://cacm.acm.org/magazines/2018/3/225475-a-programmable-...)

Funny how 'pythonic' can mean different things to different people. I've been developing in python on and off for the best part of a decade, and in my world comprehensions are considered far more 'pythonic' than map/filter/lambda.