def func(raw_input()):
#stuff goes here..
Why can't you use raw_input() as a parameter?
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Just what are you trying to accomplish? The code you posted is semantically inconsistent.Prune– Prune2016-12-15 20:47:25 +00:00Commented Dec 15, 2016 at 20:47
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I'm not trying to accomplish anything. I was going to Zed's "Learn Python the hard way" and I thought about this when reading on functions and parameters.Dumi B– Dumi B2016-12-15 20:48:39 +00:00Commented Dec 15, 2016 at 20:48
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1what would you expect that code to do if it was valid? If it means "get raw input to use as an argument when this function is called" then how would you reference the string inputted?Tadhg McDonald-Jensen– Tadhg McDonald-Jensen2016-12-15 20:51:38 +00:00Commented Dec 15, 2016 at 20:51
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Please explain what you would expect this code to do. What you posted is simply illegal syntax. Without knowing what you have in mind, the answer to "why can't you use this" is "because it's illegal", which isn't a particularly useful answer.Prune– Prune2016-12-15 20:54:36 +00:00Commented Dec 15, 2016 at 20:54
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3 Answers
Because the return value of a function call is semantically distinct from a parameter. raw_input() returns a string; a parameter must be an identifier that takes on the value passed in.
Comments
You can't.
BTW, You could falsely think that using named parameters could work:
def func(s=raw_input()):
print(s)
func()
func()
then only problem is that it just seems to work. First time calling func(), s is evaluated by prompting you to enter a string.
Second time, default value for s is known and you're not prompted.
answered Dec 15, 2016 at 20:53
3 Comments
David Zemens
what about
def func(s=raw_input): return s()?Jean-François Fabre
that would work! but you may as well
return raw_input(). I was just pointing out that you shouldn't force python to do stuff like that :)David Zemens
Oh I agree it's silly to do either way :) and it would be preferable to bind
raw_input() to a name within the function.Try this strange OOP solution.
class Runnable:
def __init__(self,function, *args, **kwargs):
self.function = function
self.args = args
self.kwargs = kwargs
def run(self):
return self.function(*self.args, **self.kwargs)
Runnable Loads up an object with a function and arguments. .run() executes when you're ready.
Here is its usage:
def func(runnable_thing):
print(runnable_thing.run())
super_raw = Runnable(raw_input, "Please Type your Input: ")
func(super_raw) # prints input from raw
The cool thing is that the Runnable class I made works on other functions with larger params as well.
import datetime
foo = Runnable(datetime.datetime, 2016, 12, 15 ) ## foo is not yet a datetime object
bar = foo.run() ## bar is a datetime object
If you're not a fan of the .run() at the end of it, then we can follow Deloith's suggestion to use __call__() to make Runnable feel like a function.
class Runnable:
def __init__(self,function, *args, **kwargs):
self.function = function
self.args = args
self.kwargs = kwargs
def __call__(self):
return self.function(*self.args, **self.kwargs)
From this point on, it really feels like we've created a new function.
def func(runnable_thing):
print(runnable_thing())
super_raw = Runnable(raw_input, "Please Type your Input: ")
func(super_raw) # prints input from raw
Try that on for size, and let me know how you like it.
1 Comment
Delioth
I'd personally add on that you wouldn't necessarily want it to be a
run() function that must be named to be used, but implement the magic hook __call__(), which lets an object pretend it's a function so you could call foo=Runnable(...); foo()