3 ms·

I agree wholeheartedly with the first half of your comment, but the second half is the same uninformed dogma you rail against in the first! Python is not reall

by blasdel 17y ago

I agree wholeheartedly with the first half of your comment, but the second half is the same uninformed dogma you rail against in the first! Python is not really a functional programming language -- it has statements and suites, neither of which are first-class. lambda is implemented as an inline (suite-less) value-returning statement (like the ternary statement) because dealing with indentation would be a bitch. Since statements cannot contain other statements outside of suites, it's impossible to implement full-fledged anonymous functions in the language grammar without breaking something. While I'd love TCO in python, I like the stack traces better (ever dealt with a stray head [] in GHC?).

erlanger 17y ago
> first-class. I'm not sure I follow. This looks first-class to me. def name_printer(name): def printer(): print(name) return printer erlanger_printer = name_printer('erlanger') Python doesn't support creating anonymous functions, but functions are first-class. Sorry if you already knew this; it seems like you know Python pretty well so I'm sure you do.
- blasdel 17y ago
  Of course functions are first-class, and the lambda statement does return anonymous functions. Functions in Python are just objects that have a __call__ method, and methods are just functions partially-applied to the object they are bound on -- LOVELY METACIRCULARITY What aren't first class are statements and suites (indented blocks of expressions) -- they're part of the syntax and thus can't be constructed or referred to. Particularly nasty is the way non-value-returning statements can't be used in expressions passed to other statements. Your example is perfect -- in Python < 3, print is a statement and not a built-in function! # this is invalid syntax: name_printer = lambda x: lambda: print x # with print as a function it works: from __future__ import print_function name_printer = lambda x: lambda: print(x)
  - erlanger 17y ago
    Nice explanation. Note that I did wrap my print arg in parens, however. When I heard they were changing it to a function in 3 I made this a habit.
    - blasdel 17y ago
      Using parens that way with the print statement is a bad idea. You aren't using it like a function -- the parens are parsed as an expression. statement function print(1) 1 1 print(1,2) (1, 2) 1 2 print(1,2), 3 (1, 2) 3 SyntaxError Just use the old syntax, and let 2to3 take care of you when the time comes.
      - erlanger 17y ago
        I don't think I've ever used print that way. If I need to print more than one thing, it's clearer to use regular string formatting. Thanks for clarifying that though, interesting.

by blasdel 17y ago

erlanger 17y ago

> first-class. I'm not sure I follow. This looks first-class to me. def name_printer(name): def printer(): print(name) return printer erlanger_printer = name_printer('erlanger') Python doesn't support creating anonymous functions, but functions are first-class. Sorry if you already knew this; it seems like you know Python pretty well so I'm sure you do.

blasdel 17y ago
Of course functions are first-class, and the lambda statement does return anonymous functions. Functions in Python are just objects that have a __call__ method, and methods are just functions partially-applied to the object they are bound on -- LOVELY METACIRCULARITY What aren't first class are statements and suites (indented blocks of expressions) -- they're part of the syntax and thus can't be constructed or referred to. Particularly nasty is the way non-value-returning statements can't be used in expressions passed to other statements. Your example is perfect -- in Python < 3, print is a statement and not a built-in function! # this is invalid syntax: name_printer = lambda x: lambda: print x # with print as a function it works: from __future__ import print_function name_printer = lambda x: lambda: print(x)
- erlanger 17y ago
  Nice explanation. Note that I did wrap my print arg in parens, however. When I heard they were changing it to a function in 3 I made this a habit.
  - blasdel 17y ago
    Using parens that way with the print statement is a bad idea. You aren't using it like a function -- the parens are parsed as an expression. statement function print(1) 1 1 print(1,2) (1, 2) 1 2 print(1,2), 3 (1, 2) 3 SyntaxError Just use the old syntax, and let 2to3 take care of you when the time comes.
    - erlanger 17y ago
      I don't think I've ever used print that way. If I need to print more than one thing, it's clearer to use regular string formatting. Thanks for clarifying that though, interesting.