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TODO: check out presentation from PyCon 2019 introducing it. |
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| From [[https://dustingram.com/talks/2019/04/04/the-walrus-operator/|PEP 572: The Walrus Operator [Pycon 2019]]]: | |
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| {{{#!highlight python numbers=off # Instead of: |
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| y = f(x) foo = [] if y: foo = [y, y**2, y**3] # use foo = [y := f(x), y**2, y**3] ### # Instead of results = [] for x in data: r = f(x) if r : results.append(result) # use results [ y for x in data if (y := f(x)) ] |
Python Walrus operator
Good examples of the Python walrus operator.
From: https://www.reddit.com/r/Python/comments/1rw18i5/comment/oaxdl2e/
# perfect for re.match
if has_whatever := re.match(stuff)
a, b = has_whatever.groups()
###
only call other_function if res is some value
if (result := some_fun()) in ("a", "b"):
other_function(res)
###
# conditional based on the result of res
if func(res := gfunc()):
# use res safely
###
while line := fp.readline():
...
###
if bad := [r for r in records if r.bad()]:
raise ValueError('Bad records: ' + ', '.join(b.name for b in bad))
From PEP 572: The Walrus Operator [Pycon 2019]:
# Instead of:
y = f(x)
foo = []
if y:
foo = [y, y**2, y**3]
# use
foo = [y := f(x), y**2, y**3]
###
# Instead of
results = []
for x in data:
r = f(x)
if r :
results.append(result)
# use
results [
y for x in data
if (y := f(x))
]
