On Wed, Apr 28, 2010 at 1:31 AM, GZ <zyzhu2...@gmail.com> wrote:
> I am looking at the following code:
>
> def fn():
>
> def inner(x):
> return tbl[x]
>
> tbl={1:'A', 2:'B'}
> f1 = inner # I want to make a frozen copy of the values of tbl
> in f1
> tbl={1:'C', 2:'D'}
> f2 = inner
> return (f1,f2)
>
> f1,f2 = fn()
> f1(1) # output C
> f2(1) # output C
>
> What I want is for f1 to make a frozen copy of tbl at the time f1 is
> made and f2 to make another frozen copy of tbl at the time f2 is made.
> In other words, I want f1(1)=='A' and f2(1)=='C'.
>
> One way to do this is to use functools.partial
>
> def fn():
>
> def inner(tbl, x):
> return tbl[x]
>
> tbl={1:'A', 2:'B'}
> f1 = functools.partial(inner,tbl) # I want to make a frozen copy
> of the values of tbl in f1
> tbl={1:'C', 2:'D'}
> f2 = functools.partial(inner,tbl)
> return (f1,f2)
>
> I am wondering if there is any other way to do this.
I prefer the functools.partial() method personally, but the other
obvious way to go about it is:
def fn():
tbl={1:'A', 2:'B'}
f1 = lambda x, table=tbl: table[x]
tbl={1:'C', 2:'D'}
f2 = lambda x, table=tbl: table[x] # we have to be repetitive
return (f1,f2)
Note that default argument values are evaluated exactly once, at
definition-time.
The lambdas can equivalently be replaced with def-s of course.
Cheers,
Chris
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