python eval to target specific class variable at runtime

Question

I'm trying to bind a variable to a specific list within a class at runtime. The snippet below works, but I'd like to have the class name in the eval expression instead of the variable. i.e. the equivalent of:

mybin = 'bin2'
eval(foo.mybin)

which obviously won't work... but I can't seem to figure out the syntax after various incarnations of trying to glue "foo' and "mybin' together.

class A:
    bin1 = [3,6,9]
    bin2 = [12,14,25]

foo = A()

mybin = 'foo.bin2'

for bin in eval(mybin):
    print bin

outputs:

 12
 14
 25

Daniel · Accepted Answer · 2017-12-10 21:54:11Z

2

Don't use eval. For dynamic attribute access, python knows getattr:

mybin = 'bin2'
for bin in getattr(foo, mybin):
    print bin

answered Dec 10, 2017 at 21:54

Daniel

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1 Comment

Dan F. Over a year ago

Hazards of old / other language programming habits! I'm new to python and had not run across getattr before. Thanks for the tip!

zipa · Accepted Answer · 2017-12-10 21:57:44Z

1

Maybe f-string is what you might be fond of:

class A():
  bin1 = [1, 2]
  bin2 = [12, 14, 25]

foo = A()

my_bin = 'bin2'

print(eval(f'foo.{my_bin}'))
#[12, 14, 25]

answered Dec 10, 2017 at 21:57

zipa

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