Re: Read any function in runtime
On Fri, 23 Oct 2009 17:39:40 +0100, Matt McCredie mccre...@gmail.com wrote: joao abrantes senhor.abrantes at gmail.com writes: Hey. I want to make a program like this:print Complete the function f(x)=then the user would enter x+2 or 1/x or any other function that only uses the variable x. Then my python program would calculate f(x) in some points for example in f(2),f(4).. etc . How can I do this? check out 'eval' or 'exec'. Then check out all the reasons you shouldn't use them in an environment that you don't trust absolutely -- if someone wipes your hard disc, you won't get any sympathy from here. The safe answer is to write yourself a small parser. Given that you've got a very limited symbol set, that shouldn't be too hard. -- Rhodri James *-* Wildebeest Herder to the Masses -- http://mail.python.org/mailman/listinfo/python-list
Re: Read any function in runtime
Rhodri James rhodri at wildebst.demon.co.uk writes: On Fri, 23 Oct 2009 17:39:40 +0100, Matt McCredie mccredie at gmail.com wrote: joao abrantes senhor.abrantes at gmail.com writes: Hey. I want to make a program like this:print Complete the function f(x)=then the user would enter x+2 or 1/x or any other function that only uses the variable x. Then my python program would calculate f(x) in some points for example in f(2),f(4).. etc . How can I do this? check out 'eval' or 'exec'. Then check out all the reasons you shouldn't use them in an environment that you don't trust absolutely -- if someone wipes your hard disc, you won't get any sympathy from here. The safe answer is to write yourself a small parser. Given that you've got a very limited symbol set, that shouldn't be too hard. This should only be a concern if it is some sort of client/server app (like a web-app). If this is something that is going to be run on a local machine then the person running it could do just as much damage via the command line. While I agree that there is a danger if the input might come from untrusted users, and the original poster should be aware of that, writing your own parser only makes sense in those instances. If this application is run locally then users have access to the machine anyway. I don't want to give a (potentially) new user to python the impression that they need to be writing their own parser to solve this problem. It depends on where the input is coming from. Two things to note: 1. eval and exec are perfectly safe if the input is from a trusted source. 2. eval and exec are never safe if the input is not from a trusted source. Matt McCredie -- http://mail.python.org/mailman/listinfo/python-list
Re: Read any function in runtime
Matt McCredie wrote: Rhodri James rhodri at wildebst.demon.co.uk writes: On Fri, 23 Oct 2009 17:39:40 +0100, Matt McCredie mccredie at gmail.com wrote: joao abrantes senhor.abrantes at gmail.com writes: Hey. I want to make a program like this:print Complete the function f(x)=then the user would enter x+2 or 1/x or any other function that only uses the variable x. Then my python program would calculate f(x) in some points for example in f(2),f(4).. etc . How can I do this? check out 'eval' or 'exec'. Then check out all the reasons you shouldn't use them in an environment that you don't trust absolutely -- if someone wipes your hard disc, you won't get any sympathy from here. The safe answer is to write yourself a small parser. Given that you've got a very limited symbol set, that shouldn't be too hard. This should only be a concern if it is some sort of client/server app (like a web-app). If this is something that is going to be run on a local machine then the person running it could do just as much damage via the command line. While I agree that there is a danger if the input might come from untrusted users, and the original poster should be aware of that, writing your own parser only makes sense in those instances. If this application is run locally then users have access to the machine anyway. I don't want to give a (potentially) new user to python the impression that they need to be writing their own parser to solve this problem. It depends on where the input is coming from. Two things to note: 1. eval and exec are perfectly safe if the input is from a trusted source. 2. eval and exec are never safe if the input is not from a trusted source. Matt McCredie I'd like to add that there are several lisp apps out there that give you a REPL (for example stumpwm). A REPL could be seen as a sophisticated `eval' loop. Case in point, it is common in the lisp world. You could, in theory, hose your system from inside emacs (and you may not even know it...hahaha). -Jack -- http://mail.python.org/mailman/listinfo/python-list
Read any function in runtime
Hey. I want to make a program like this: print Complete the function f(x)= then the user would enter x+2 or 1/x or any other function that only uses the variable x. Then my python program would calculate f(x) in some points for example in f(2),f(4).. etc . How can I do this? -- http://mail.python.org/mailman/listinfo/python-list
Re: Read any function in runtime
joao abrantes senhor.abrantes at gmail.com writes:
Hey. I want to make a program like this:print Complete the function
f(x)=then the user would enter x+2 or 1/x or any other function that only uses
the variable x. Then my python program would calculate f(x) in some points for
example in f(2),f(4).. etc . How can I do this?
check out 'eval' or 'exec'.
statement = raw_input(Complete the function f(x)=)
print eval(statement, {'x':2})
print eval(statement, {'x':4})
print eval(statement, {'x':6})
or with 'exec':
statement = raw_input(Complete the function f(x)=)
exec f = lambda x:+statement in {}
print f(2)
print f(4)
print f(6)
Matt McCredie
--
http://mail.python.org/mailman/listinfo/python-list
