# How can I readline a one-term polynomial from a user?

I would like to ask the user for a function. How can I do that? Is there something like readline?

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What do you mean by a "one-term polynomial"?

As for the existence of a readline, you can either use read_data to read from a file, or any Python method to read data from a file. You can also read from the standard input, and then process the data you get. In particular, if you have a string representation s of some object of a class C, you can usually construct the object using C(s). For instance, if you define R.<x> = ZZ[], then R('x^2 + x + 1') returns the polynomial x^2 + x + 1. Using eval(s) will have the same effect here (since x is known to SageMath as the generator of the polynomial ring).

I would like the user to type a function in(the user of the programme).

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In Python, you can read a string from the user prompt with the function raw_input:

sage: a = raw_input()
2*x+3

sage: a
'2*x+3'

sage: type(a)
<type 'str'>


Then you can transform that string into a symbolic expression:

sage: b = SR(a)
sage: b
2*x + 3

sage: type(b)
<type 'sage.symbolic.expression.Expression'>

sage: sin(b)
sin(2*x + 3)


You can put it within a function:

sage: def user_square():
....:     print 'Please enter a function to be squared: ',
....:     a = raw_input()
....:     return SR(a)^2

sage: user_square()
Please enter a function to be squared:  cos(d)+sin(t)
(cos(d) + sin(t))^2


If you want to make something fancy, with input boxes and sliders, you can have a look at Sage interact.

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