4 ms·

You're not coming across as argumentative. By poor support for higher-order functions, I mean that e.g. you have to do "from functools import reduce, partial"

You're not coming across as argumentative. By poor support for higher-order functions, I mean that e.g. you have to do "from functools import reduce, partial" for fold or partial function application. It's a trivial complaint, I'll give you, but it's one that's bitten me on more than one occasion (you think I'd learn!). There's also no foldr unless you implement it yourself. I badly misspoke when I said that you could pickle comprehensions, because what I meant was that the language gives you no hint that you might be able to. Pickling sum([ os.stat(f).st_size for f in os.listdir(".") ]) is obviously (I hope) not going to work. On the other hand pickling [ lambda n: n % 2 == 0 ] intuitively ought to, since pickling [ isEven ] would work fine. I've had to rewrite a couple of modules because of this - again, maybe I should have learnt from my mistakes - but it gives me the general impression of "avoid lambdas and functions that regularly use lambdas, because they're occasionally a lot of unexpected work".

icebraining 14y ago
I don't understand. You can't pickle functions; when you pickle a function, you get a reference to the function, not the actual function code. E.g., this doesn't work: Dump.py: def isEven(n): return n % 2 == 0 import pickle with open('pickled','w') as dumpfile: pickle.dump(isEven, dumpfile) Loader.py import pickle with open('pickled') as loadfile: isEven = pickled.load(loadfile) This throws AttributeError: 'module' object has no attribute 'isEven' What you can do is marshal the function's code: import marshal marshal.dump(isEven.func_code, file) #Then to load isEven = types.FunctionType(marshal.load(file), globals()) But you can also dump a lambda's code: import marshal marshal.dump((lambda n: n % 2 == 0).func_code, file) #Loading is the same isEven = types.FunctionType(marshal.load(file), globals()) isEven(4) So frankly, I don't get the problem with lambdas.
- hythloday 14y ago
  When you pickle a function, you get a reference to the function, not the actual function code. Right - that's usually what I want. (I've used pickle to store tests against game assets, e.g. that a model has all of its textures checked into perforce, or that a texture for a model does not exceed 128x128, unless otherwise specified). Marshalling functions is usually a non-starter for this, since a) it's complicated to analyse the call graph before execution, and b) native functions can't be marshalled - an awful lot of code executed against this asset pipeline is thin bindings over native/Java/C# code. Maybe I have found the 1% of the Python use-cases where lambdas suck a bit and everywhere else it's fine--it would be great if my experience was exceptional and no-one else had ever had a similar problem doing something else.
  - icebraining 14y ago
    Oh, ok. I don't know how Python could pickle a reference to an anonymous function, 'though.

icebraining 14y ago

I don't understand. You can't pickle functions; when you pickle a function, you get a reference to the function, not the actual function code. E.g., this doesn't work: Dump.py: def isEven(n): return n % 2 == 0 import pickle with open('pickled','w') as dumpfile: pickle.dump(isEven, dumpfile) Loader.py import pickle with open('pickled') as loadfile: isEven = pickled.load(loadfile) This throws AttributeError: 'module' object has no attribute 'isEven' What you can do is marshal the function's code: import marshal marshal.dump(isEven.func_code, file) #Then to load isEven = types.FunctionType(marshal.load(file), globals()) But you can also dump a lambda's code: import marshal marshal.dump((lambda n: n % 2 == 0).func_code, file) #Loading is the same isEven = types.FunctionType(marshal.load(file), globals()) isEven(4) So frankly, I don't get the problem with lambdas.

hythloday 14y ago
When you pickle a function, you get a reference to the function, not the actual function code. Right - that's usually what I want. (I've used pickle to store tests against game assets, e.g. that a model has all of its textures checked into perforce, or that a texture for a model does not exceed 128x128, unless otherwise specified). Marshalling functions is usually a non-starter for this, since a) it's complicated to analyse the call graph before execution, and b) native functions can't be marshalled - an awful lot of code executed against this asset pipeline is thin bindings over native/Java/C# code. Maybe I have found the 1% of the Python use-cases where lambdas suck a bit and everywhere else it's fine--it would be great if my experience was exceptional and no-one else had ever had a similar problem doing something else.
- icebraining 14y ago
  Oh, ok. I don't know how Python could pickle a reference to an anonymous function, 'though.