exec behaviour inside a class method

Asked Sep 03 '16 at 16:49

Active Sep 03 '16 at 16:49

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Why does exec fail to run this code, when it's called inside of a class method?

class test(object):
    def run(self):
        exec("f=lambda n:(n>15and f(n//16)or'')+'HBKD'[n//4%4]+'OAEI'[n%4];print(f(156))")

exec("g=lambda n:(n>15and g(n//16)or'')+'HBKD'[n//4%4]+'OAEI'[n%4];print(g(156))")
t = test()
t.run()

The exec call outside of the class works properly, but the call inside the run() function fails, and gives an NameError: 'NameError: name 'f' is not defined'. Why's that?

asked Sep 03 '16 at 16:49

Yytsi

You can't set new local names with exec in a function, because locals are heavily optimised. – Martijn Pieters Sep 03 '16 at 16:51
That's why if you execute it in `globals()` (or a custom namespace) with `exec("f=lambda n:(n>15and f(n//16)or'')+'HBKD'[n//4%4]+'OAEI'[n%4];print(f(156))", globals())` you're good to go. – Dimitris Fasarakis Hilliard Sep 03 '16 at 16:52
@MartijnPieters I actually looked at that post for a while, but thought that I was in a different situation due to the class I have. Thanks! – Yytsi Sep 03 '16 at 16:53
@Jim Makes sense now. Thanks! – Yytsi Sep 03 '16 at 16:54
@TuukkaX: you can trivially reproduce the same error without the class. – Martijn Pieters Sep 03 '16 at 16:54
@MartijnPieters Yup. I just thought differently upon asking. – Yytsi Sep 03 '16 at 16:56

exec behaviour inside a class method

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