[python] Can we have assignment in a condition?
Nope, the BDFL didn't like that feature.
From where I sit, Guido van Rossum, "Benevolent Dictator For Life”, has fought hard to keep Python as simple as it can be. We can quibble with some of the decisions he's made -- I'd have preferred he said 'No' more often. But the fact that there hasn't been a committee designing Python, but instead a trusted "advisory board", based largely on merit, filtering through one designer's sensibilities, has produced one hell of a nice language, IMHO.
Is it possible to have assignment in a condition?
For ex.
if (a=some_func()):
# Use a
Not directly, per this old recipe of mine -- but as the recipe says it's easy to build the semantic equivalent, e.g. if you need to transliterate directly from a C-coded reference algorithm (before refactoring to more-idiomatic Python, of course;-). I.e.:
class DataHolder(object):
def __init__(self, value=None): self.value = value
def set(self, value): self.value = value; return value
def get(self): return self.value
data = DataHolder()
while data.set(somefunc()):
a = data.get()
# use a
BTW, a very idiomatic Pythonic form for your specific case, if you know exactly what falsish value somefunc may return when it does return a falsish value (e.g. 0), is
for a in iter(somefunc, 0):
# use a
so in this specific case the refactoring would be pretty easy;-).
If the return could be any kind of falsish value (0, None, '', ...), one possibility is:
import itertools
for a in itertools.takewhile(lambda x: x, iter(somefunc, object())):
# use a
but you might prefer a simple custom generator:
def getwhile(func, *a, **k):
while True:
x = func(*a, **k)
if not x: break
yield x
for a in getwhile(somefunc):
# use a
One of the reasons why assignments are illegal in conditions is that it's easier to make a mistake and assign True or False:
some_variable = 5
# This does not work
# if True = some_variable:
# do_something()
# This only works in Python 2.x
True = some_variable
print True # returns 5
In Python 3 True and False are keywords, so no risk anymore.
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