How to simplify a variable's fraction value in Python

Question

I have a variable called b who's value is determined as so: b = float(input("What is your y-intercept?")). Later in the file, I want to take the value of b (assuming it is a float) and convert it to a fraction like this: print(Fraction(b)). I know that something like print(Fraction(0.45)) will print 8106479329266893/18014398509481984, but print(Fraction('0.45')) will print 9/20. How can I have that same result with a variable? Doing print(Fraction('b')) gives me this error: ValueError: Invalid literal for Fraction: 'b'.

Code:

from fractions import Fraction

elif equation == 'slope':    
    slope = input("Do you need to find slope? Type 'yes' or 'no'.")

    if slope == 'yes':
       y2 = float(input("What's your y2 value?:"))
       y1 = float(input("What is your y1 value?"))
       x2 = float(input("What is your x2 value?:"))
       x1 = float(input("What is your x1 value?:"))

        m = y2-y1/x2-x1
        print(str(m))
    elif slope == 'no':
        m = input("What is the slope?")

    b = float(input("What is your y-intercept?"))
    m = str(m)
    b = str(b)
    print("Your equation is: y = {}x + {}".format(m,b))
    simplify = input("Do you want to simplify this to standard form? Type in 'yes' or 'no'")

    if simplify == 'yes':
        m = float(m)
        b = float(b)
        if m < 0:
            pos_m = m*-1
        if isinstance(b, float):
            print(Fraction(b)) #Works, but not what I want
            print(Fraction('b')) #Does not work 

Answer 1

Fraction(str(b))

This is how you convert the variable's value (rather than its *name) to a string.