# 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?

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?

0

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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Asked: ** 2017-11-24 09:08:11 +0200 **

Seen: **423 times**

Last updated: **Nov 24 '17**

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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).