Evaluating dynamically generated statements in Python

Question

I need to dynamically generate python code and execute it with eval() function.

What I would like to do is to generate some "imports" and "assign values". I mean, I need to generate this string to evaluate it eval(x).

x = """ import testContextSummary import util.testGroupUtils testDb = [testContextSummary.TestContextSummary, testGroupUtils.testGroupUtils.TestGroupUtils] """ # x is automatically generated eval(x) ... use testDb ...

I tried with this code, but eval() returns an error not recognizing import, so I tried this code.

x = """ testContextSummary = __import__("testContextSummary") testGroupUtils = __import__("util.testGroupUtils") testDb = [testContextSummary.TestContextSummary, testGroupUtils.testGroupUtils.TestGroupUtils] """ # x is automatically generated eval(x) # error

I again got an error not allowing assignment statement.

Is there any way to execute dynamically generated python script, and use the result from the evalution?

mgilson · Accepted Answer · 2013-06-06 00:36:07Z

3

You want exec instead of eval.

>>> s = "x = 2" >>> exec s >>> x 2

Of course, please don't use exec on untrusted strings ...

edited Jun 6, 2013 at 0:36

answered Jun 6, 2013 at 0:30

mgilson

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2 Comments

martineau Over a year ago

prosseek: It's because exec() can handle multiple lines of Python, whereas eval() only evaluates a single expression. Be safe.

mgilson Over a year ago

@martineau: I didn't see the original comment, but the same caveats with exec apply equally to eval and it has nothing to do with multiple lines of code ... (__import__('os').remove('important_file'))

perreal · Accepted Answer · 2013-06-06 00:45:05Z

0

This may also work:

x = """[ __import__("testContextSummary").TestContextSummary, __import__("util.testGroupUtils").testGroupUtils.TestGroupUtils] """ testDB=eval(x)

answered Jun 6, 2013 at 0:45

perreal

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1 Comment

martineau Over a year ago

While that might work in this particular case, things could get tricky if there were multiple names defined or there was more complicated logic in the dynamically generated code, like if/else constructs and/or function/class definitions, etc -- all of which exec() ought to be able to handle.

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