python exec() with an if statement

Question

I'm trying to find a way to exec() an if statement.

So, for example:

exampleCode = "if 0 < 1:"

exec(exampleCode)
    print("Zero is less than one")

Now, obviously this isn't possible with exec(). But is it with something similar?

Something else that would work would be:

exampleCode = "if 0 < 1:"

exampleCode
    print("Zero is less than one")

Again, this isn't possible, because variables cannot be code.

So, again, is there something else that may work?

Answer 1

You can do this, sort of, with eval:

exampleCode = "0 < 1"
if eval(exampleCode):
    print("Zero is less than one")

...but it's unclear what the benefit is of doing this (that is, there's something you're not showing us that motivates your question).

Answer 2

Use a lambda (an anonymous function). We can pass an arbitrary lambda which allows dynamically evaluating a condition in the scope in which it is evaluated:

# 1) A lambda with 0 args; this is silly because it will always evluate to a constant
cond_0args = lambda: 0 < 1
# <function <lambda> at 0x1084ffc80>

# 2) A lambda with 2 args:
cond = lambda x, y: x<y

# ... you could of course have a lambda with 3 args or whatever
#cond = lambda x, y, z: some_expression_involving_x_y_z

if cond_0args():
    print("Zero is less than one")

or, more sensibly:

if cond(0,1):
    print("Zero is less than one")