Python: Read the content of a variable [duplicate]

Question

This question already has answers here:

Running Python code contained in a string (4 answers)

Closed 9 years ago.

For example I have:

x = True and True
print x

I want to be able to do something like:

x = True and True
print "The answer to ", some_function(x), "is", x

Such that the program reads:

The answer to True and True is True.

Is there a some_function() that can read the content as a string instead of solving as a boolean?

Sorry in advance for any confusion on the wording of the question.

• John Gordon: You mean you have a Python expression stored as a string? Like x = 'True and True'? In that case, look at eval().

Answer 1

You can write it as a string:

x = 'True and True'

and evaluate it using eval:

print "The answer to ", x, "is", eval(x)

---

>>> x = 'True and True'
>>> print "The answer to ", x, "is", eval(x)
The answer to True and True is True

• skrrgwasme: It may be worth adding the usual warning about eval: it shouldn't be used on untrusted input. For example, if x is populated from a web service and the result is going into a log, the input must be sanitized (as much as possible) before running it through eval.

Answer 2

What you're asking for is basically not possible in Python; expressions are evaluated immediately in Python and the interpreter does not "remember" what expression generated a particular value.

However, by changing your code slightly you can achieve a similar effect with eval:

expr = 'True and True'
print "The answer to", expr, "is", eval(expr)

As usual, with eval, never pass anything that you didn't write yourself (because it opens a security hole otherwise).