Josh Rosenberg added the comment: This is a natural consequence of Python using reference semantics.
x = y just makes x and y references to the same object. For immutable objects like int and str, you'll never notice consequences of this, since changes to the value (x += 1) replace the reference in x with a new reference. But for mutable objects like lists, you need to explicitly copy (shallow or deep) to avoid a dependency of the sort you've encountered. For the specific case of sequences, the empty slice is the simplest, fastest way to perform a shallow copy: x = y[:] For other built-in types, you can often call .copy() or wrap in the constructor: newdict = olddict.copy() # or dict(olddict) For more complex cases, the copy module offers shallow and deep copy abilities (via the copy and deepcopy function) for arbitrary data structures. ---------- nosy: +josh.rosenberg _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue21943> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
