python3 print() in exec()

Question

In python3, when I run

>>> exec("","","")
TypeError: exec() arg 2 must be a dict, not str
>>> exec( "print('Hello')", print("World"), print("!") )
World
!
Hello
>>> type(print("World"))
World
<class 'NoneType'>

I mean in the Python3, the arg2 of exec() expects a dict, but we can still put a print() function which is not a dict. why?

score 7 · Accepted Answer · edited May 30 '13 at 21:00

7

Simple!

It's acceptable because its value is None (it can accept None or a dict), which is the default value for the argument.

In a example, a call such as:

exec("print('Hello')")

Is the same as:

exec("print('Hello')", None, None)

edited May 30 '13 at 21:00

glglgl

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answered May 30 '13 at 19:58

Fernando Jorge Mota

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score 3 · Answer 2 · answered May 30 '13 at 19:59

3

print returns None, which is a valid argument for an optional parameter.

answered May 30 '13 at 19:59

Asad Saeeduddin

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python3 print() in exec()

2 Answers2