Say I have a list with mathematical operators in it, like this
operators = ['+','-','*','/']
And I am taking a random operator from here, like this
op = random.choice(operators)
If I take two numbers, say 4 and 2, how can I get Python to do the mathematical operation (under the name 'op') with the numbers?
You better do not specify the operators as text. Simply use lambda expressions, or the operator module:
import operator
import random
operators = [operator.add,operator.sub,operator.mul,operator.floordiv]
op = random.choice(operators)You can then call the op by calling it with two arguments, like:
result = op(2,3)For example:
>>> import operator
>>> import random
>>>
>>> operators = [operator.add,operator.sub,operator.mul,operator.floordiv]
>>> op = random.choice(operators)
>>> op
<built-in function sub>
>>> op(4,2)
2
So as you can see, the random picked the sub operator, so it subtracted 2 from 4.
In case you want to define an function that is not supported by operator, etc. you can use a lambda-expression, like:
operators = [operator.add,lambda x,y:x+2*y]So here you specified a function that takes the parameters x and y and calculates x+2*y (of course you can define an arbitrary expression yourself).
operator.div. It is either operator.floordiv or operator.truediv (see here for a list of operators).You can use eval if you are absolutely certain that what you are passing to it is safe like so:
num1 = 4
num2 = 2
operators = ['+','-','*','/']
op = random.choice(operators)
res = eval(str(num1) + op + str(num2))
Just keep in mind that eval executes code without running any checks on it so take care. Refer to this for more details on the topic when using ast to do a safe evaluation.
eval(..) is considered dangerous. You better avoid it, unless you have absolutely no choice.
literal_eval won't work with all operators, try ast.literal_eval('2*3'); I'm actually surprised it works with + and -