String formatting with quotation marks

Question

Say I have a list

list = ['a', 'b', 'c']

And I want to create the following strings:

foo_a = bar['a']
foo_b = bar['b']
foo_c = bar['c']

I tried the following:

for i in list:
    print("foo_{} = bar['{{}}']".format(i))

But the output is

foo_a = bar['{}']
foo_b = bar['{}']
foo_c = bar['{}']

I have read Why is this usage of python F-string interpolation wrapping with quotes? but the second method does not seem to work anymore.

Answer 1

You have two {} place-holders but only one variable. So you need to let those place-holders know they need to use the same one. Also, for some reason you use double-braces in the second place-holder. This is used to "escape" the braces, so {{}} will become {} (and not serve as an actual place-holder).

So after fixing these two issues:

>>> list = ['a', 'b', 'c']
>>> for i in list:
        print("foo_{i} = bar['{i}']".format(i=i))
     #  print("foo_{0} = bar['{0}']".format(i))

foo_a = bar['a']
foo_b = bar['b']
foo_c = bar['c']

Or with f-strings (for Python >= 3.6):

for i in list:
    print(f"foo_{i} = bar['{i}']")

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To better understand the use of place holders, read more at PyFormat, specifically the Basic Formatting part for info about positional place-holders, and the Named place-holders part for - well - named place-holders.