Python User input equation

Question

I\'m writing a simple python script to solve differential equations using Eulers method and right now i have to change the source code every time i want to solve a new equat

Answer 1

You can use the eval in combination with lambda functions, like this:

e = eval('lambda x, y: x/y')

To actually have this interactive, use raw_input() to obtain the actual expression ('lambda x, y: x/y' in this case). Or if you prefer not to type the whole lambda wording, and provided that you'll always have the independent variable x and the dependent variable y, in an equation like y = f(x), you could write something like this:

e = eval('lambda x, y: ' + raw_input('enter equation for y=f(x): '))

And then you'd enter the 'x/y' when you're prompted to.

However, are you sure you need it inside the while loop?

Answer 2

Tack för exempel -- that allowed me to determine what you need.

Yes, this is possible. Read in the equation as a string variable, such as

equation = input("Enter your equation here")

Then when you want to find a value for e, use the Python eval method:

e = eval(equation)

Be very careful with this method: eval() is powerful, and very discriminating about what it accepts.

• eval is really dangerous
• Security on untrusted strings