What Does = (equal) Do In F-strings Inside The Expression Curly Brackets?
Solution 1:
This is actually a brand-new feature as of Python 3.8.
Added an
=
specifier to f-strings. An f-string such asf'{expr=}'
will expand to the text of the expression, an equal sign, then the representation of the evaluated expression.
Essentially, it facilitates the frequent use-case of print-debugging, so, whereas we would normally have to write:
f"some_var={some_var}"
we can now write:
f"{some_var=}"
So, as a demonstration, using a shiny-new Python 3.8.0 REPL:
>>>print(f"{foo=}")
foo=42
>>>
Solution 2:
From Python 3.8, f-strings support "self-documenting expressions", mostly for print de-bugging. From the docs:
Added an = specifier to f-strings. An f-string such as f'{expr=}' will expand to the text of the expression, an equal sign, then the representation of the evaluated expression. For example:
user = 'eric_idle' member_since = date(1975, 7, 31) f'{user=}{member_since=}'"user='eric_idle' member_since=datetime.date(1975, 7, 31)"
The usual f-string format specifiers allow more control over how the result of the expression is displayed:
>>>delta = date.today() - member_since>>>f'{user=!s}{delta.days=:,d}' 'user=eric_idle delta.days=16,075'
The = specifier will display the whole expression so that calculations can be shown:
>>>print(f'{theta=}{cos(radians(theta))=:.3f}') theta=30 cos(radians(theta))=0.866
Solution 3:
This was introduced in python 3.8. It helps reduce a lot of f'expr = {expr}
while writing codes. You can check the docs at What's new in Python 3.8.
A nice example was shown by Raymond Hettinger in his tweet:
>>> from math import radians, sin
>>> for angle in range(360):
print(f'{angle=}\N{degree sign} {(theta:=radians(angle))=:.3f}')
angle=0° (theta:=radians(angle))=0.000
angle=1° (theta:=radians(angle))=0.017
angle=2° (theta:=radians(angle))=0.035
angle=3° (theta:=radians(angle))=0.052
angle=4° (theta:=radians(angle))=0.070
angle=5° (theta:=radians(angle))=0.087
angle=6° (theta:=radians(angle))=0.105
angle=7° (theta:=radians(angle))=0.122
angle=8° (theta:=radians(angle))=0.140
angle=9° (theta:=radians(angle))=0.157
angle=10° (theta:=radians(angle))=0.175
...
You can also check out this to get the underlying idea on why this was proposed in the first place.
Solution 4:
As mention here:
Equals signs are now allowed inside f-strings starting with Python 3.8. This lets you quickly evaluate an expression while outputting the expression that was evaluated. It's very handy for debugging.:
It mean it will run the execution of the code in the f-string braces, and add the result at the end with the equals sign.
So it virtually means:
"something={executed something}"
Post a Comment for "What Does = (equal) Do In F-strings Inside The Expression Curly Brackets?"