如何在python中获取无理数作为用户输入？

Question

How to get a irrational number as a user input in python? Like squared root of 2

something like :

Irrational_Number = float(input("ENTER a Irrational Number : "))
   >>> ENTER a Irrational Number : (USER INPUT)

and then user put a Number like N-th root of K (i mean the number in this format not the exactly this kind of String) " Pi " , " e " or " Phi " in command Line.

How User Can do this Directly in command line python (3.8)

I searched this question everywhere but there is nothing about that...

Answer 1

First of all, you're casting your input to a float , so to be precise (which is important if we're bandying around terms like Irrational Number ) then we have to highlight the assumption that were talking about approximations to Irrational Numbers here.

That done, there's a few ways you can explore a solution:

The first would be to define a namespace in which you map string names to numeric equivalents - a simple dict could do the trick, like:

numbers_as_words  = { "e",2.718281828459045
                      "pi",3.141592653589793
                      "phi",1.618033988749895
                      "sqr2",1.4142135623730951
                      "feet_to_meters",0.3048
                      "lbs_to_kg",0.453592
                      "miles_to_kilometers",1.60934
                      "gallons_to_litres",3.78541 }

I've padded that out with some non-irrational place-holders too, in case you wanted to embed some simple conversion type logic.

Then, you'd need to take your input as a string, perform a simple replace function on the string to resolve any matching strings, and viola , you've got a mixed numeric/string input method.

def replace_names_and_return_float(user_input, mapping):
    for k,v in mapping.items():
        user_input = user_input.replace(k,str(v))
    return float(user_input)

Irrational_Number = replace_names_and_return_float(input("ENTER a Irrational Number : "), numbers_as_words )

Then it's just up to you to maintain that numbers_as_words dictionary to contain all the substitutions you want to recognise. That could get tedious, but it ought to be enough to get you started.

If you find some official list of irrational number approximations, you might be able to download it, and construct a numbers_as_words mapping as an automated process, but I've not Googled that just now.

Answer 2

Please find below code snippet:

import re
g = input("Enter your irrational number : ") 
if g=='pi':
    g=math.pi
elif "root" in g:
    root=float(re.search('[0-9]+', g).group())
    number=float(re.search('(\d+)(?!.*\d)', g).group())
    g=number**(1/float(root))
print(g)

Advantage of using this would be:

1. There is no manual value inserted
2. You can build it for every symbol present in math lib
3. Can be extended for other operations as well