Convert ast node into python object

Question

Given an ast node that can be evaluated by itself, but is not literal enough for ast.literal_eval e.g. a list comprehension

src = '[i**2 for i in range(10)]'
a = ast.parse(src)

Now a.body[0] is an ast.Expr and a.body[0].value an ast.ListComp. I would like to obtain the list that eval(src) would result, but given only the ast.Expr node.

Answer 1

Perhaps you're looking for compile()? The result of calling compile() on an AST object is a code object that can be passed to eval().

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>>> src = '[i**2 for i in range(10)]'
>>> b = ast.parse(src, mode='eval')
>>> eval(compile(b, '', 'eval'))
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

• Kyss Tao: I tried but did not seem to get it working. E.g. compile(a.body[0],'','eval') gave the error expected Expression node, got Expr. (Is Expr not just short for Expression?)
• Amber: No - Expr is what is contained in the body of an Expression. Try just passing a instead of a.body[0]. (From the grammar.)
• Amber: Try using ast.parse(src, mode='eval') to get an Expression object.
• Kyss Tao: about your edit: if I change the mode to 'eval' I get problems other-where in my code