You can turn a string into code by using pythons So be sure that you build in reasonable security into this.<\/p>\n You can define a function that takes a string and returns a function. It seems better to define allowed and supported words than blacklisting some:<\/p>\n Result:<\/p>\neval<\/code> function, but this is dangerous and generally considered bad style<\/strong>, See this: https:\/\/stackoverflow.com\/a\/661128\/3838691.
\nIf user can input the string, they could input something like
\nimport subprocess; subprocess.check_call(['rm', '-rf', '*'], shell=True)<\/code>.<\/p>\n
\nWe need to do a little preprocessing to allow the user to input formulas more like he is used to (^ etc.):<\/p>\nEdit: Second version \u2013 white list instead of blacklist<\/h2>\n
import re\n\nreplacements = {\n 'sin' : 'np.sin',\n 'cos' : 'np.cos',\n 'exp': 'np.exp',\n 'sqrt': 'np.sqrt',\n '^': '**',\n}\n\nallowed_words = [\n 'x',\n 'sin',\n 'cos',\n 'sqrt',\n 'exp',\n]\n\ndef string2func(string):\n ''' evaluates the string and returns a function of x '''\n # find all words and check if all are allowed:\n for word in re.findall('[a-zA-Z_]+', string):\n if word not in allowed_words:\n raise ValueError(\n '\"{}\" is forbidden to use in math expression'.format(word)\n )\n\n for old, new in replacements.items():\n string = string.replace(old, new)\n\n def func(x):\n return eval(string)\n\n return func\n\n\nif __name__ == '__main__':\n\n func = string2func(input('enter function: f(x) = '))\n a = float(input('enter lower limit: '))\n b = float(input('enter upper limit: '))\n x = np.linspace(a, b, 250)\n\n plt.plot(x, func(x))\n plt.xlim(a, b)\n plt.show()\n<\/code><\/pre>\n$ python test.py\nenter function: f(x) = x^2\nenter lower limit: 0\nenter upper limit: 2\n<\/code><\/pre>\n
![\"enter](\"https:\/\/jassweb.com\/solved\/wp-content\/uploads\/2022\/08\/Solved-How-to-plot-a-math-function-from-string.png\")
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