Kent Johnson schrieb: > Schüle Daniel wrote: >> and now the obvious one (as I thought at first) >> >> >>> lst=[] >> >>> for i in range(10): >> ... lst.append(lambda:i) >> ... >> >>> lst[0]() >> 9 >> >>> i >> 9 >> >>> >> >> I think I understand where the problem comes from >> lambda:i seems not to be fully evalutated >> it just binds object with name i and not the value of i >> thus lst[0]() is not 0 > > The problem is that variables in closures are not bound until the > variable goes out of scope. So each lambda is bound to the final value > of i. >> >> are there other solutions to this problem >> without use of eval or exec? > > The workaround is to use a default argument to bind the current value of i: > In [1]: lst = [] > > In [2]: for i in range(10): > ...: lst.append(lambda i=i: i) > ...: > ...: > > In [3]: lst[0]() > Out[3]: 0 > > In [4]: lst[5]() > Out[4]: 5 > > A list comp makes this IMO cleaner: > In [5]: lst = [ lambda i=i: i for i in range(10) ] > > In [6]: lst[0]() > Out[6]: 0 > > In [7]: lst[5]() > Out[7]: 5 > > Kent
many thanks for the explaination, it look much simpler than my solutions too Daniel -- http://mail.python.org/mailman/listinfo/python-list
