I need to pass inequalities to a function for evaluation within the function. Is there a way to evaluation the inequality if passed as a string? Or must I pass a representation of the inequality and use if/else statements to generate the sign?
Your question is a little vague, but it sounds like you want to evaluate a string containing an expression (such as x > 5). Rather than doing that, which is unnecessarily complex, and potentially a security hazard, just define a function, either in the conventional way or using lambda.
def gt5(x):
return x > 5
or
gt5 = lambda x: x > 5
These are both equivalent; now you can pass around gt5 however you like, and when the time comes, you simply call it
y = 6
if gt5(y):
...
As Gerrat's answer suggests, the operator module may also be useful for things like this.
Now that I know you are processing user strings, I would definitely suggest creating a dictionary that maps strings to functions. (Perhaps that's what you meant in your title?) Passing userland strings into getattr seems bad in a number of ways. What happens if you want to add a string that doesn't correspond to an attribute of operator? What happens if the user passes in a string corresponding to a private attribute? Better to create a custom dictionary mapping strings to functions. A dict allows you to specify just those strings you want to accept.
func_dict = {
'lt' : operator.lt,
'gt' : operator.gt,
'nand' : lambda x, y: not (x and y)
}
You could still save yourself work by using getattr + operator to build the dict from a list of strings that you want to accept. Something like:
func_dict = dict((s, getattr(operator, s)) for s in ['lt', 'gt'])
Then update func_dict like so:
custom_dict = {
'nand' : lambda x, y: not (x and y)
}
func_dict.update(custom_dict)
From there you can easily call functions in the dict like so:
>>> func_dict['lt'](5, 7)
True