Python has an input() function. Using this function at runtime, the user can enter values ​​that the function returns as a string. Using the type conversion functions from these strings, you can get an integer, a floating point number, and so on. For example, a = int(input()) . But how to make the user enter functions like A sin (2πƒt + Ø)?

After entering the function, various operations will be performed on it (calculating values, plotting graphs, and so on).

2 answers 2

Depending on what you want to do with the entered formulas - I would pay attention to two modules: SymPy for analytic and numerical solution of equations, graphing and much more, and NumExpr for fast and safe numerical calculation of the entered formulas with numpy, scipy support , arrays, variables, etc.

Example of using numexpr

examples of using NumExpr with Numpy arrays:

 import numpy as np import numexpr as ne In [84]: a, b = np.random.rand(2, 5) In [85]: a Out[85]: array([ 0.05399168, 0.85873638, 0.73317032, 0.17825897, 0.83083985]) In [86]: b Out[86]: array([ 0.19115417, 0.66216767, 0.51021111, 0.5816862 , 0.72958694]) In [87]: ne.evaluate('sin(a)**2 + cos(a)**2') Out[87]: array([ 1., 1., 1., 1., 1.])

matrix multiplication:

 In [92]: m1 = np.array([[1,2], [3,4]]) In [93]: m2 = np.array([[10, 10]]) In [94]: m1 Out[94]: array([[1, 2], [3, 4]]) In [95]: m2 Out[95]: array([[10, 10]]) In [96]: ne.evaluate('m1 * m2') Out[96]: array([[10, 20], [30, 40]], dtype=int32)

SymPy usage examples :

 from sympy import * x, y, z, t = symbols('xyz t')

open brackets:

 In [75]: ((x+y)**2 * (x+1)).expand() Out[75]: x**3 + 2*x**2*y + x**2 + x*y**2 + 2*x*y + y**2

simplify the expression:

 In [76]: simplify((x**2 - y**2) / (x - y)**2) Out[76]: (x + y)/(x - y)

equation solution:

 In [77]: solve(Eq(x**3 + 2*x**2 + 4*x + 8, 0), x) Out[77]: [-2, -2*I, 2*I]

solving a system of linear equations:

 In [78]: solve([Eq(x + 5*y, 2), Eq(-3*x + 6*y, 15)], [x, y]) Out[78]: {x: -3, y: 1}

analytical solution of indefinite integral:

 In [79]: integrate(x**2 * cos(x), x) Out[79]: x**2*sin(x) + 2*x*cos(x) - 2*sin(x)

or

 In [100]: init_printing(use_unicode=False, wrap_line=False, no_global=True) In [101]: intgrl = Integral(sin(1/x), (x, 0, 1)).transform(x, 1/x) In [102]: intgrl Out[102]: oo / | | sin(x) | ------ dx | 2 | x | / 1

...

    You can try it in a simple way.

     import math from math import sin from math import pi c = eval(input('sin(2*pi*(x+y))')) print (c)
    • five
      In any answer with eval, it is always worth mentioning its insecurity - andreymal