Why is this usage of python F-string interpolation wrapping with quotes?

Question

Code in question:

a = 'test'

# 1)
print(f'{a}') # test

# 2)
print(f'{ {a} }') # {'test'}

# 3)
print(f'{{ {a} }}') # {test}

My question is, why does case two print those quotes?

I didn't find anything explicitly in the documentation. The closest thing I found detailing this was in the PEP for this feature:

(the grammar for F-strings)

f ' <text> { <expression> <optional !s, !r, or !a> <optional : format specifier> } <text> ... '

The expression is then formatted using the format protocol, using the format specifier as an argument. The resulting value is used when building the value of the f-string.

I suppose that the value of a is being formatted with some formatter, which, since the data type is a string, wraps it with quotes. This result is then returned to the surrounding F-string formatting instance.

Is this hypothesis correct? Is there some other place which documents this more clearly?

Your link to 2.7 doc will not have anything about a 3.6 feature. Instead, docs.python.org/3.6/reference/lexical_analysis.html#f-strings — Terry Jan Reedy
– Terry Jan Reedy, Commented Jul 14, 2017 at 22:08

jwodder · Accepted Answer · 2017-07-14 21:55:19Z

10

In f'{ {a} }', the {a} (as indicated by the grammar) is interpreted as a Python expression. In Python, {a} constructs a set of one element (a), and the stringification of a set uses the repr of its elements, which is where the quotes come from.

answered Jul 14, 2017 at 21:55

jwodder

58.1k12 gold badges116 silver badges134 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Terry Jan Reedy Over a year ago

Nested {}s are recognized as a nested replacement field only in the optional format specification (after ':'). That they have their normal meaning in the replacement expression, and result in a set, can be verified by executing print(f'{ { {a} } }')

Collectives™ on Stack Overflow

Why is this usage of python F-string interpolation wrapping with quotes?

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related