Python eval() builtin function

Question

After looking for some reference online I still do not understand how eval() really works, maybe I am missing a key component, hopefully someone can guide me to the right docs or explanation.

Suppose:

def foo(x,y):
    print(x)
    print(y)

Use eval() to call foo().

Example 1:

eval('foo(1,2)')

Example 2:

eval('foo')(1,2)

According to python 3.6 documentation, the way I am calling eval() on example is how it should be done, as I am passing everything as a string, However, for example #2 I still do not understand why python interpreter also evaluates correctly.To me when running eval() on the second example the python interpreter should return a TypeError requiring 2 missing arguments. I am hoping if someone can point me in the right direction.

foo is a valid Python expressions. Functions are just another type of object. Try it in the interpreter — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Jul 4, 2018 at 22:25

Ned Batchelder · Accepted Answer · 2018-07-04 22:21:44Z

5

This is a valid Python expression: foo. It evaluates to the function. You can then call it. This is why foo(1, 2) works. You can also do this:

x = foo
x(1, 2)

So eval("foo") evaluates to the function foo, which you can then call.

answered Jul 4, 2018 at 22:21

Ned Batchelder

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