How to reference variable dynamically in Python?

Question

I have the following code:

PROJECT_ID = 'test'
BQ_TABLE_NAME_CATEGORIES = 'categories'
BQ_TABLE_NAME_MANUFACTURERS = 'manufacturers'
list = [BQ_TABLE_NAME_CATEGORIES, BQ_TABLE_NAME_MANUFACTURERS]
table_categories = PROJECT_ID + '.'  + BQ_TABLE_NAME_CATEGORIES
table_manufacturers = PROJECT_ID + '.' + BQ_TABLE_NAME_MANUFACTURERS

for table in list:
    ....
    source_objects=['table_{0}'.format(table)]  #reference to the correct var
    ....

This however puts string inside source_objects. I want it to reference the variables (whatever is saved in the variables) meaning what I actually want is equivalent of this:

When table = BQ_TABLE_NAME_CATEGORIES

source_objects = [ table_categories ]

When table = BQ_TABLE_NAME_MANUFACTURERS

source_objects = [ table_manufacturers ]

Are you trying to get the contents on table_categories inside a list? Or do you just want to reference it's string value? — saud
– saud, Commented Dec 19, 2018 at 9:24
Also, it is bad practice to override the built-in list object. — saud
– saud, Commented Dec 19, 2018 at 9:25
@RottenCandy I want the refrence... source_objects should contain whatever table_categories contains.. Just like I would do : source_objects = [ table_categories ] — Luis
– Luis, Commented Dec 19, 2018 at 9:26

Avishay Cohen · Accepted Answer · 2018-12-19 09:40:23Z

5

you can use the eval() function to turn strings into variable: read on eval

PROJECT_ID = 'test'
BQ_TABLE_NAME_CATEGORIES = 'categories'
BQ_TABLE_NAME_MANUFACTURERS = 'manufacturers'
mylist = [BQ_TABLE_NAME_CATEGORIES, BQ_TABLE_NAME_MANUFACTURERS]
table_categories = PROJECT_ID + '.'  + BQ_TABLE_NAME_CATEGORIES
table_manufacturers = PROJECT_ID + '.' + BQ_TABLE_NAME_MANUFACTURERS

for table in mylist:
    source_objects=eval('table_{0}'.format(table)) #reference to the correct var
    print source_objects

output:

test.categories
test.manufacturers

also as noted in comments, you really shouldn't override list, and use mylist or whatever instead

answered Dec 19, 2018 at 9:40

Avishay Cohen

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Comments

saud · Accepted Answer · 2018-12-19 09:44:14Z

3

If I understand your question correctly, what you are trying to do is store the values of table_categories and table_manufacturers inside a list called source_objects. Assuming the table_... variables are global,

suffixes = [BQ_TABLE_NAME_CATEGORIES, BQ_TABLE_NAME_MANUFACTURERS]

source_objects = []
for s in suffixes:
    source_objects.append(globals['table_{0}'.append(s)])
    ...

This would get you:

>>> source_objects
['test.categories', 'test.manufacturers']

And if the table_... variables are not global, use locals(). See https://docs.python.org/3/library/functions.html#globals

answered Dec 19, 2018 at 9:44

saud

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