[Tutor] exec('a=1') in functions

[Jan Kenin]

Hello,

in python 2.7 the following code works:
 >>> def f( b ):
...     exec( 'a=%s'%b )
...     print 'a=', a
...
 >>> f( 1 )
a= 1

in python3.6 this works in the interpreter:
 >>> b=1
 >>> exec('a=%s'%b)
 >>> a
1

but not in a function:
 >>> def f( b ):
...     exec( 'a=%s'%b )
...     print( 'a=', a )
...
 >>> f( 1 )
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "<stdin>", line 3, in f
NameError: name 'a' is not defined

How can I get the latter working?

Thanks for all advice!
Jan