Python define function within function

Question

I would like to define a function within a function, and call it from out of the function. Here is a simplified version of my code:

def make_func():
    exec('def test(text):\n\tprint(text)')


make_func()
test("Hello")

When I run this code, I get this error:

Traceback (most recent call last):
line 6, in <module>
    test("Hello")
NameError: name 'test' is not defined

Thank you in advance for your help.

why would you want to do that? i think test is defined only in the scope of the exec — DanielM, Aug 18 '19 at 19:18
What's the point? What purpose are you trying to achieve, that you couldn't achieve by defining functions the normal way? (And why did you bring `exec` into this?) — user2357112, Aug 18 '19 at 19:36
This is a simplified version of my actual code, in which I have to dynamically create a function from within a function. I don't NEED to use `exec()`, but I can't think of another way to do this — SomeMosa, Aug 18 '19 at 19:41

Matthew E. Miller · Answer 1 · 2019-08-18T19:53:48.567

1

Revision:

You need to add test to the global namescape. Here is the solution:

def make_func():
    exec('def test(text):\n\tprint(text)', globals())


make_func()
test("Hello")

NOTE: This has been asked before.

Previous:

See Python exec(). You cannot call text("Hello) because text() has fallen out-of-scope and is no longer defined. It's only defined within the scope of exec().

However, you could do this:

def make_func():
    exec('def test(text):\n\tprint(text)\ntest("Hello")')


make_func()

Or:

def make_func(text):
    exec('def test(text):\n\tprint(text)\ntest(text)')


make_func("Hello")

Hope that helps.

edited Aug 18 '19 at 19:53

answered Aug 18 '19 at 19:24

Matthew E. Miller

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I am looking to call the function from outside the `exec()` statement, but thank you for this suggestion – SomeMosa Aug 18 '19 at 19:26
I am saying, that is not possible. Functions defined within exec() are only available within the scope of exec(). See link. – Matthew E. Miller Aug 18 '19 at 19:28
Is there another function I can use instead of `exec()`? – SomeMosa Aug 18 '19 at 19:28
I cannot imagine there is, but I do not know. I think it's unlikely. – Matthew E. Miller Aug 18 '19 at 19:31
This isn't right. Names defined inside an exec can be used outside it. – 8n8 Aug 18 '19 at 19:40
Please provide evidence. – Matthew E. Miller Aug 18 '19 at 19:43
["the code is executed in the current scope"](https://docs.python.org/3/library/functions.html#exec) – 8n8 Aug 18 '19 at 19:47
`exec('test = "Hello"')` would create a variable called `test` with the value of `"Hello"`. The command `print(test)` prints `"Hello"`, even though the `print()` function is outside of the `exec()` – SomeMosa Aug 18 '19 at 19:49
I added a revision. You can use the function, but you need to explicitly change the scope. – Matthew E. Miller Aug 18 '19 at 19:51
Thank you for your suggestion! I was unaware of what to search for, which could explain the duplicate question – SomeMosa Aug 18 '19 at 19:56

DjaouadNM · Accepted Answer · 2019-08-18T19:51:25.597

0

test function is defined inside the make_func function and thus is local to it, to make it global (reachable from anywhere in the code) use (for Python 2.7):

def make_func():
    exec('def test(text):\n\tprint(text)')
    globals()['test'] = test

make_func()
test("Hello")  #  ==>  Hello

For Python 3.x:

def make_func():
    exec('def test(text):\n\tprint(text)', globals())

make_func()
test("Hello")  #  ==>  Hello

edited Aug 18 '19 at 19:51

answered Aug 18 '19 at 19:33

DjaouadNM

22,013
4
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I just get this error: `line 3, in make_func globals()['test'] = test NameError: name 'test' is not defined` – SomeMosa Aug 18 '19 at 19:35
@Pokechu48 It works with Python 2.7, I'll see a workaround with Python 3.x. – DjaouadNM Aug 18 '19 at 19:46
@Pokechu48 Check the edit for a workaround for Python 3.x. – DjaouadNM Aug 18 '19 at 19:52

Python define function within function

2 Answers2