eval() does not bind variables in lambda expressions
correctly:

>>>def f(g): return eval('lambda x: g(x)')
>>>f(lambda y: y * 2)(17)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "<string>", line 1, in <lambda>
NameError: global name 'g' is not defined

The docs say this about eval():

# If both dictionaries are omitted, the expression is
# executed in the environment where eval is called.

and using plain local variables work as expected:

>>>def h(d): return eval('d(10)')
>>>h(lambda y: y * 2)
20

Also, if locals() is presented as the global dict to
eval(), it works:

>>>def f(g): return eval('lambda x: g(x)', locals(),
locals())
>>>f(lambda y: y * 2)(17)
34

but this does not allow the expression to reference
global variables of course.