[Numpy-discussion] How to use user input as equation directly

[djxvillain]

Hello all,

I am an electrical engineer and new to numpy. I need the ability to take in
user input, and use that input as a variable. For example:

t = input('enter t: ')
x = input('enter x: ')

I need the user to be able to enter something like x =
2*np.sin(2*np.pi*44100*t+np.pi/2) and it be the same as if they just typed
it in the .py file. There's no clean way to cast or evaluate it that I've
found.

I could make a function to parse this string character by character, but I
figured this is probably a common problem and someone else has probably
figured it out and created an object for it. I can't find a library that
does it though.

If I can provide any more information please let me know. Thank you in
advance for your help.



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[Ryan May]

Post by djxvillain
Hello all,
I am an electrical engineer and new to numpy. I need the ability to take in
t = input('enter t: ')
x = input('enter x: ')
I need the user to be able to enter something like x =
2*np.sin(2*np.pi*44100*t+np.pi/2) and it be the same as if they just typed
it in the .py file. There's no clean way to cast or evaluate it that I've
found.

Are you aware of Python's eval function:
https://docs.python.org/3/library/functions.html#eval

?

Ryan

[djxvillain]

That worked perfectly. I've been googling how to do this, I guess I didn't
phrase it correctly. Thank you very much. You just saved me a ton of time.



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[John Ladasky]

This isn't just a Numpy issue. You are interested in Python's eval().

Keep in mind that any programming language that blurs the line between code
and data (many do not) has a potential security vulnerability. What if
your user doesn't type

"x = 2*np.sin(2*np.pi*44100*t+np.pi/2)"

but instead types this:

"import os ; os.remove('/home')"

I do NOT recommend that you eval() the second statement.

You can try to write code which traps unwanted input before you eval() it.
It's apparently quite hard to stop everything bad from getting through.

Post by djxvillain
Hello all,
I am an electrical engineer and new to numpy. I need the ability to take in
t = input('enter t: ')
x = input('enter x: ')
I need the user to be able to enter something like x =
2*np.sin(2*np.pi*44100*t+np.pi/2) and it be the same as if they just typed
it in the .py file. There's no clean way to cast or evaluate it that I've
found.
I could make a function to parse this string character by character, but I
figured this is probably a common problem and someone else has probably
figured it out and created an object for it. I can't find a library that
does it though.
If I can provide any more information please let me know. Thank you in
advance for your help.
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n7.nabble.com/How-to-use-user-input-as-equation-directly-tp43665.html
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[Benjamin Root]

Perhaps the numexpr package might be safer? Not exactly meant for this
situation (meant for optimizations), but the evaluator is pretty darn safe.

Ben Root

Post by John Ladasky
This isn't just a Numpy issue. You are interested in Python's eval().
Keep in mind that any programming language that blurs the line between
code and data (many do not) has a potential security vulnerability. What
if your user doesn't type
"x = 2*np.sin(2*np.pi*44100*t+np.pi/2)"
"import os ; os.remove('/home')"
I do NOT recommend that you eval() the second statement.
You can try to write code which traps unwanted input before you eval()
it. It's apparently quite hard to stop everything bad from getting through.

Post by djxvillain
Hello all,
I am an electrical engineer and new to numpy. I need the ability to take in
t = input('enter t: ')
x = input('enter x: ')
I need the user to be able to enter something like x =
2*np.sin(2*np.pi*44100*t+np.pi/2) and it be the same as if they just typed
it in the .py file. There's no clean way to cast or evaluate it that I've
found.
I could make a function to parse this string character by character, but I
figured this is probably a common problem and someone else has probably
figured it out and created an object for it. I can't find a library that
does it though.
If I can provide any more information please let me know. Thank you in
advance for your help.
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n7.nabble.com/How-to-use-user-input-as-equation-directly-tp43665.html
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*Research Scientist*
*International Technological University*
*2711 N. First St, San Jose, CA 95134 USA*
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[Robert McLeod]

Post by Benjamin Root
Perhaps the numexpr package might be safer? Not exactly meant for this
situation (meant for optimizations), but the evaluator is pretty darn safe.

It would not be able to evaluate something like 'np.arange(50)' for
example, since it only has a limited subset of numpy functionality. In the
example provided that or linspace is likely the natural input for the
variable 't'.

[djxvillain]

This will not be a public product and will only be used by other
engineers/scientists for research. I don't think security should be a huge
issue, but I appreciate your input and concern for the quality of my code.



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[Benjamin Root]

"only be used by engineers/scientists for research"

Famous last words. I know plenty of scientists who would love to "do
research" with an exposed eval(). Full disclosure, I personally added a
security hole into matplotlib thinking I covered all my bases in protecting
an eval() statement.

Ben Root

Post by djxvillain
This will not be a public product and will only be used by other
engineers/scientists for research. I don't think security should be a huge
issue, but I appreciate your input and concern for the quality of my code.
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tp43665p43670.html
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[Ben Rowland]

It is important to bear in mind where the code is being run - if this is something running on a researcher’s own system, they almost certainly have lots of other ways of messing it up. These kind of security vulnerabilities are normally only relevant when you are running code that came from somewhere else.

That being said, this use case sounds like it could work with the Jupyter notebook. If you want something that is like typing code into a .py file but evaluated at run time instead, why not just use an interactive Python REPL instead of eval(input()).

Ben

Post by Benjamin Root
"only be used by engineers/scientists for research"
Famous last words. I know plenty of scientists who would love to "do research" with an exposed eval(). Full disclosure, I personally added a security hole into matplotlib thinking I covered all my bases in protecting an eval() statement.
Ben Root
This will not be a public product and will only be used by other
engineers/scientists for research. I don't think security should be a huge
issue, but I appreciate your input and concern for the quality of my code.
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