[Python] Python recognise with and without quotation marks

I have this line of code that works.

price = df1.loc[:, ['price', 'date']]


I need to emulate this is as a loop with other metrics like sales and revenue. Is this possible? i.e How do I get Python to reference a word in the list both with and without quotation marks?

listx = [price,sales, revenue]
for a in listx:
a = df1.loc[:, ['a', 'date']]

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