3 ms·

Could you write something more on metaprogramming in Python ? And how does this compare with Lisp, what do you use it for ? Any good resources to learn this ?

by alwalo 7y ago

pdonis 7y ago
Metaprogramming is a fairly broad term, but some of the kinds of things I often find myself doing in Python are: - Writing functions that make functions: often I'll find that I want a family of functions that all follow a the same general pattern. In Lisp this would generally be done with a macro; in Python it can usually be done by writing a function that returns a function. The "maker" function will generally have some parameters that fill in specific parts of the general pattern; the function that gets returned is therefore a closure over those parameters (i.e., it has specific values of them filled in). Doing this with a "maker" function is less error prone (particularly if there are a large number of variations on the general pattern) and follows the DRY (don't repeat yourself) principle, which I think is a very good one. - Writing decorators that add a particular common behavior (such as logging or debug output) to a variety of different functions or classes or methods. This is a common case. (In fact one could argue that decorators in general are examples of metaprogramming.) - Using data to construct code. Database programming is a common application of this: for example, I have a database library I commonly use (it's on GitLab here: https://gitlab.com/pdonis/plib3-dbtools https://gitlab.com/pdonis/plib3-dbtools) which constructs typed namedtuples specific to a database table's fields, and wraps rows returned from queries in them for easier field access. More complicated database ORMs use similar techniques. Unfortunately I don't know of any good resources on metaprogramming in general.
- BoiledCabbage 7y ago
  It seems extremely perplexing that you describe how you'd solve the problem using first-class functions in Python, but then wouldn't simply use first class functions in LISP...The language that invented first class functions. It's possible LISP was more complex because you weren't comfortable with using it?
- lispm 7y ago
  > Python it can usually be done by writing a function that returns a function (defun make-incr-functions (numbers) (mapcar (lambda (n) (lambda (arg) (+ arg n))) numbers)) Why would I write it as a macro?

Could you write something more on metaprogramming in Python ? And how does this compare with Lisp, what do you use it for ? Any good resources to learn this ?

by alwalo 7y ago

Could you write something more on metaprogramming in Python ? And how does this compare with Lisp, what do you use it for ? Any good resources to learn this ?

pdonis 7y ago

Metaprogramming is a fairly broad term, but some of the kinds of things I often find myself doing in Python are: - Writing functions that make functions: often I'll find that I want a family of functions that all follow a the same general pattern. In Lisp this would generally be done with a macro; in Python it can usually be done by writing a function that returns a function. The "maker" function will generally have some parameters that fill in specific parts of the general pattern; the function that gets returned is therefore a closure over those parameters (i.e., it has specific values of them filled in). Doing this with a "maker" function is less error prone (particularly if there are a large number of variations on the general pattern) and follows the DRY (don't repeat yourself) principle, which I think is a very good one. - Writing decorators that add a particular common behavior (such as logging or debug output) to a variety of different functions or classes or methods. This is a common case. (In fact one could argue that decorators in general are examples of metaprogramming.) - Using data to construct code. Database programming is a common application of this: for example, I have a database library I commonly use (it's on GitLab here: https://gitlab.com/pdonis/plib3-dbtools https://gitlab.com/pdonis/plib3-dbtools) which constructs typed namedtuples specific to a database table's fields, and wraps rows returned from queries in them for easier field access. More complicated database ORMs use similar techniques. Unfortunately I don't know of any good resources on metaprogramming in general.

BoiledCabbage 7y ago
It seems extremely perplexing that you describe how you'd solve the problem using first-class functions in Python, but then wouldn't simply use first class functions in LISP...The language that invented first class functions. It's possible LISP was more complex because you weren't comfortable with using it?
lispm 7y ago
> Python it can usually be done by writing a function that returns a function (defun make-incr-functions (numbers) (mapcar (lambda (n) (lambda (arg) (+ arg n))) numbers)) Why would I write it as a macro?