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6. eval () evaluates the passed string as a Python expression and returns the result. For example, eval ("1 + 1") interprets and executes the expression "1 + 1" and returns the result (2). One reason you might be confused is because the code you cited involves a level of indirection.
Jul 6, 2009 · For example, if I had to deal with such dynamic Python sources, I'd reach for the ast module -- ast.literal_eval is MUCH safer than eval (you can call it directly on a string form of the expression, if it's a one-off and relies on simple constants only, or do node = ast.parse(source) first, then keep the node around, perhaps munge it with suitable visitors e.g. for variable lookup, then literal_eval the node) -- or, once having put the node in proper shape and vetted it for security issues ...
Nov 16, 2017 · While eval only allows you to evaluate a string that contains a single expression, you can eval a whole statement, or even a whole module that has been compiled into bytecode; that is, with Python 2, print is a statement, and cannot be evalled directly:
Nov 22, 2014 · 61. eval() will allow malicious data to compromise your entire system, kill your cat, eat your dog and make love to your wife. There was recently a thread about how to do this kind of thing safely on the python-dev list, and the conclusions were: It's really hard to do this properly.
It seems simple to me: eval is a vector for code injection, and is dangerous in a way that most other Python functions are not. That doesn't mean you shouldn't use it at all, but I think you should use it judiciously. Using eval is weak, not a clearly bad practice. It violates the "Fundamental Principle of Software".
ast.literal_eval raises an exception if the input isn't a valid Python datatype, so the code won't be executed if it's not. Use ast.literal_eval whenever you need eval . You shouldn't usually evaluate literal Python statements.
Feb 1, 2020 · 393. model.eval() is a kind of switch for some specific layers/parts of the model that behave differently during training and inference (evaluating) time. For example, Dropouts Layers, BatchNorm Layers etc. You need to turn them off during model evaluation, and .eval() will do it for you. In addition, the common practice for evaluating ...
By the way, there are many ways to avoid using exec/eval if all you need is a dynamic name to assign, e.g. you could use a dictionary, the setattr function, or the locals() dictionary: >>> locals()['y'] = 1 >>> y 1
Dec 1, 2009 · Yes - when there is no other way to accomplish the given task with a reasonable level of clarity and within a reasonable number of lines of code. This eliminates 99% of cases where eval is used, across the board in all languages and contexts. answered Dec 1, 2009 at 15:32. yfeldblum. 65.4k12131169.
Oct 16, 2015 · c = MyObj() c.eval("func1(42)+func2(24)") in Python..i.e. have func1() and func2() be evaluated within the scope of the object 'c' (if they were member functions within that class definition)? I can't do a simple parsing, since for my application the eval strings can become arbitrarily complicated.
