On 2月1日, 下午1时20分, alex23 <wuwe...@gmail.com> wrote: > alex23 <wuwe...@gmail.com> wrote: > > keakon <kea...@gmail.com> wrote: > > > def h2(x=[]): > > > y = x > > > y.append(1) > > > return y + [] > > > Are you aware that 'y = x' _doesn't_ make a copy of [], that it > > actually points to the same list as x? > > Sorry, I meant to suggest trying the following instead: > > def h2(x=None): > if x is None: x = [] > x.append(1) > return x + [] > > It's a common idiom to use None as a sentinel for this situation, esp. > where you _don't_ want a default mutable object to be reused.
Thank you, I got it. The default value is mutable, and can be reused by all each call. So each call it will append 1 to the default value, that's very different than C++. -- http://mail.python.org/mailman/listinfo/python-list
