default mutable arguments

[Gigs_]

I read that this is not the same:
if arg is None: arg = []
arg = arg or []


def functionF(argString="abc", argList = None):
if argList is None: argList = [] # < this
...
def functionF(argString="abc", argList=None):
argList = argList or [] # and this
...

Why?


thanks !!!

 

[Leif K-Brooks]

I read that this is not the same:
def functionF(argString="abc", argList = None):
if argList is None: argList = [] # < this
...
def functionF(argString="abc", argList=None):
argList = argList or [] # and this
...

Why?

If argList is a false value besides None ("", [], {}, False, etc.), the
second example will replace it with an empty list.

 

[Bruno Desthuilliers]

Gigs_ a écrit :

I read that this is not the same:
if arg is None: arg = []
arg = arg or []


def functionF(argString="abc", argList = None):
if argList is None: argList = [] # < this
...
def functionF(argString="abc", argList=None):
argList = argList or [] # and this
...

Why?

def test(arg=None):
foo = arg or []
print "arg : ", arg, " - foo : ", foo

test()
test(arg=0)
test(arg=False)
test(arg=())
test(arg={})
test(arg='')

etc...