The walrus operator := (also known as "assignment expression") should be used
with caution as it can easily make code more difficult to understand and thus maintain. In such case it is advised to refactor the code and use an
assignment statement (i.e. =) instead.
This rule raises an issue when the walrus operator is used in a way which makes the code confusing, as described in PEP 572.
Noncompliant Code Example
# using an assignment expression (:=) as an assignment statement (=) is more explicit
(v := f(p)) # Noncompliant
v0 = (v1 := f(p)) # Noncompliant
# using an assignment expression in a function call when keyword arguments are also used.
func(a=(b := f(p))) # Noncompliant
func(a := f(p), b=2) # Noncompliant
def func(param=(p := 21)): # Noncompliant
pass
# using an assignment expression in an annotation
def func(param: (p := 21) = 3): # Noncompliant
pass
# using assignment expression in an f-string. Character ":" is also used as a formatting marker in f-strings.
f'{(x:=10)}' # Noncompliant
f'{x:=10}' # No issue raised but still not recommended. This is not an assignment expression. '=10' is passed to the f-string formatter.
Compliant Solution
v = f(p)
v0 = v1 = f(p)
value = f(p)
func(a=value)
func(value, b=2)
def func(param=21):
p = 21
p = 21
def func(param: p = 3):
pass
x = 10
f'{x}'
See
