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bpo-41045: Add documentation for f-string's self documenting expressions #21464

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bpo-41045: Add documentation for f-string's self documenting expressions #21464

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bpo-41045: Add documentation for f-string's self documenting expressions
rishi93 Jul 13, 2020
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bpo-41045: Add documentation for f-string's self documenting expressions
rishi93 Jul 13, 2020
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bpo-41045: Add documentation for f-string's self documenting expressions
rishi93 Jul 13, 2020
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24 changes: 24 additions & 0 deletions Doc/reference/lexical_analysis.rst
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Expand Up @@ -758,6 +758,30 @@ include expressions.
>>> foo.__doc__ is None
True

F-strings can also help with "printf-style" debugging.

@ericvsmith ericvsmith Jul 13, 2020

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I think this needs to at least describe the feature. See my 2 points in bpo-41045 for what I think needs to be included.

@amaajemyfren amaajemyfren Jul 14, 2020

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Hey @rishi93,

Would you consider adding that this is new from version 3.8?


::

>>> foo = "bar"
>>> print(f"{foo=}")
"foo='bar'"
>>> print(f"{foo = }") # preserves whitespace before and after equals sign
"foo = 'bar'"

Optional format specifiers can be placed after the equals sign.
If no format specifiers are used then :meth:`repr` is used on the expression.
If format specifier (like :20) is given, then :meth:`str` is used on the
expression. You can use the repr() with the !r format specifier

@amaajemyfren amaajemyfren Jul 14, 2020

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Hey @rishi93,

I think !r is a conversion not a format specifier.

::

>>> line = "The mill's closed"
>>> f"{line = }"
'line = "The mill\'s closed"'
>>> f"{line = :20}"
"line = The mill's closed "
>>> f"{line = !r:20}"
'line = "The mill\'s closed" '

See also :pep:`498` for the proposal that added formatted string literals,
and :meth:`str.format`, which uses a related format string mechanism.

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