Question

Here is a simple code illustrating the essence of a problem:

class test:
    def __init__(self):
        self.var = 0
    def set(self, val):
        self.var = val
        print eval('map(lambda x: self.var*x, [1,2,3,4,5])')
f = test()
f.set(10)

It says

NameError: global name 'self' is not defined

I know many people don’t like eval but in my case I have to use it because it executes a math formula from the string entered by a user during programm execution.
Any suggestions is highly appreciated! Thanks in advance!

Answer 1

Try:

eval('map(lambda x, self=self: self.var*x, [1,2,3,4,5])')

The odd self=self will create a copy of self from the outer context into the inner context (the “body” of the lambda expression).